Esta página ha sido creada por el Área de Mecánica de Fluidos de la Universidad de Málaga. En ella se detallan una serie de  charlas que hemos dado en llamar I Love Fluid Mechanics (ILFM Talks). En esta actividad, tanto estudiantes de TFG, TFM, profesores del área y de otras áreas afines, así como invitados de otras instituciones realizarán una charla sobre la investigación que desarrollan en Mecánica de Fluidos.

22/10/2024, Salón de Grados B

11:00-12:00

Patrice Meunier

Senior Researcher, CNRS, IRPHE (Marseille, France)

Geoinspired bioreactors : from Earth's precession to cell production

Inspired by the precession of the Earth, a new bladeless mixer has been designed, which consists of a tilted and rotating cylinder. The transition to turbulence in such rotating flows is strongly influenced by the Coriolis force. At specific heights of fluid, the inertial waves forced by the free surface interfere constructively leading to the resonance of a global eigen mode. It creates a strong overturning flow even for small tilt angles. At large enough Reynolds numbers, this base flow exhibits a parametric instability involving a triadic resonance. The viscous threshold of this instability can be predicted using a linear stability analysis, in excellent agreement with the experiments.

This simple set-up has been used to build large-scale mixers. The mixing is as efficient as using a classical Rushton turbine, but with a shear 20 times smaller. This soft mixer is thus particularly interesting for bioreactors which require an efficient mixing of oxygen and carbon dioxide but where a strong shear can damage fragile cells. Applications to micro-algae indicate that the growth rate is increased compared to classical bioreactors. It opens the way to a new generation of bioreactors that may be a technological breakthrough in biotechnologies.

17/10/2024, Salón de Grados B

11:00-12:00

Javier Alaminos Quesada

Investigador postdoctoral, Universidad California San Diego (UCSD)

Effects of buoyancy on the dispersion of drugs released intrathecally in the spinal canal.

In this research, we examine how drugs are transported when administered via direct injection into the cerebrospinal fluid (CSF) that fills the intrathecal space surrounding the spinal cord. Because of the small drug diffusivity, the dispersion of neutrally buoyant drugs has been shown in previous work to rely mainly on the mean Lagrangian flow associated with the CSF oscillatory motion. Attention is given here to effects of buoyancy, arising when the drug density differs from the CSF density. For the typical density differences found in applications, the associated Richardson number is shown to be of order unity, so that the Lagrangian drift includes a buoyancy-induced component that depends on the spatial distribution of the drug, resulting in a slowly evolving cycle-averaged flow problem that can be analysed with two-time scale methods. The asymptotic analysis leads to a nonlinear integro-differential equation for the spatiotemporal solute evolution that describes accurately drug dispersion at a fraction of the cost involved in direct numerical simulations of the oscillatory flow. The model equation is used to predict drug dispersion of positively and negatively buoyant drugs in an anatomically correct spinal canal, with separate attention given to drug delivery via bolus injection and constant infusion.

31/01/2024, Salón de Grados B

11:00-12:00

José Hermenegildo García Ortiz

Profesor Ayudante Doctor, Universidad de Cádiz, Escuela Superior de Ingeniería

Design a soft biomimetic robot fish based on DEAs (Dielectric elastomer actuator) devices

Research on how fish and other aquatic organisms propel themselves offers valuable natural references to improve the technology related to underwater devices such as vehicles, and biomimetic robotics.

The aim is to develop a biomimetic robot fish by means of commercial DEAs in order to complete the numerical work developed in this topic. The primary objective is to ascertain the fish’s forces during  swimming, abstaining from the utilization of motors, actuators, or any

other mechanisms that might impede the conceptualization o the  robot as well as the replication of its deformable structure. For this purpose, the behavior of this device (DEA) as well as its control must be studied. This type of device works by applying a potential  difference between two plates in which the polymeric material (elastomer) is inserted. This potential difference (input) causes the material chains themselves to be ordered, producing the compression of the material (output).

This type of actuators have a low weight and operate silently, being this a predominant advantage for our purpose. Its efficiency is high, because although it needs about 1kV to generate an output, the intensity is very low, so it has low heat losses and also avoids electromagnetic effects (as a motor could have) with the  environment.

24/11/2023, Salón de Grados B

11:00-12:00

Manuel Guerrero Hurtado

Investigador predoctoral, Universidad Carlos III de Madrid

Cost-Effective Algorithms for Modeling the Coagulation Cascade in Patient-Specific Left Atrial Flows

Cardiac thrombosis predominantly occurs in the left atrium (LA), contributing to approximately 30 % of ischemic strokes. Thrombosis is a complex process strongly regulated by the coagulation cascade. This cascade is governed by a system of dozens of 3D advection-reaction-diffusion partial differential equations (PDE), presenting computational challenges due to their high dimensionality, low diffusivity, and multi-scale nature.

In this seminar, I will introduce a novel Multi-Fidelity (MuFi) method designed to simplify the PDE system into an equivalent system of ordinary differential equations (ODE). This innovative approach characterizes species concentration as a function of the statistical moments of blood residence time. 

I will apply this methodology to a database of LA flows (N=6 patients, including 3 thrombus-negative and 3 thrombus/TIA positive cases) to quantify patient-specific thrombin production under a 9-species model for the coagulation cascade network.

Additionally, I will discuss the computational tools developed for obtaining the LA flow, including an in-house solver of the Navier-Stokes equations using the Immersed Boundary Method to model the LA walls. This solver has been accelerated using GPUs. When combined with the MuFi method, it enables an unprecedented description of thrombin concentration in the LA.

20/11/2023, Salón de Grados B

11:00-12:00

Miguel Ángel Herrada

Catedrático de Mecánica de Fluidos, Universidad de Sevilla

The Jacobian Analytical Method (JAM)

Many areas of engineering and physics require the solution of complex non-linear problems. The most robust method for solving nonlinear systems is Newton's method, which uses the Jacobian matrix of the whole system to update an approximate solution of the problem until the errors are sufficiently small. We present a numerical method for solving nonlinear problems, based on the Newton’s method, specifically adapted to free interphase tracking using analytical and elliptic mappings. The method is shown to be capable of tackling complex physical problems ranging from electrosprays to fluid-structure iteration. The application of the method to a simple convection-diffusion problem will be described in detail

06/10/2023, Salón de Grados B

11:00-12:00

Jezabel Curbelo

Contratada Ramón y Cajal, Universidad Politécnica de Barcelona

Comparing Models for Compressible Convection

 In numerical modeling of planetary and stellar convection, taking into account compressibility effects is crucial. However, using the exact equations may not be feasible due to the generation of fast acoustic waves, which distract from the slower convective motions caused by buoyancy. The Oberbeck-Boussinesq model simplifies the calculations by suppressing the acoustic waves, making it easier for numerical simulations, but it simplifies pressure effects to a secondary role. Intermediate models, such as the anelastic and anelastic liquid models, have also been proposed to balance simplicity and accuracy.

We investigated compressible convection under several different approximations for the thermodynamic state, as well as using the exact equations with different classes of equations of state (EoS). Our results are mostly discussed in the framework of mantle convection but the EoS is flexible enough to be applied to other cases.

20/06/2023, Salón de Grados B

11:00-12:00

Juan M. López 

Professor of Applied Mathematics, in Arizona State University

Parametrically forced rapidly rotating container flows

Rapidly rotating contained flows subjected to low amplitude parametric forcing, such as libration or precession modulating the rotation amplitude or direction, are ubiquitous in geophysical and astrophysical flows, as well as in many technological applications. Rapidly rotating flows, characterized by small Ekman numbers (ratio of viscous time scale to rotation time scale), support inertial waves due to the restorative Coriolis force. Low amplitude parametric forcing can extract a portion of the available rotational energy in a rapidly rotating contained body of fluid and convert it into intense fluid motions via the resonant excitation of inertial waves. The Ekman numbers of geophysical and astrophysical flows are many orders of magnitude smaller than what can be achieved in laboratory experiments, and the forcing amplitudes in experiments need to be relatively large in order to measure a signal reliably. The response flows are then dominated by viscous and nonlinear effects that may not be prevalent in the very low Ekman and low forcing amplitude regimes. Direct numerical simulations of the Navier-Stokes equations with no-slip boundary conditions are now able to simulate librating and precessing flows at Ekman numbers as small as, or smaller than, those in laboratory experiments, at small forcing amplitudes over the entire inertial range of forcing frequencies. This is opening up new insights into these fascinating flows. The talk will present an overview of recent results. 

7/06/2023, Salón de Grados B

11:00-12:00

Fermín Bañón

Profesor Ayudante Doctor,  Área de Ingeniería de los procesos de fabricación (UMA)

Estudiio del mecanizado por chorro de agua con abrasivo (AWJM) de estructuras híbridas y operaciones de texturizado para activación superficial. 

En la actualidad, existe un interés creciente en combinar materiales disímiles para formar estructuras híbridas (Aleación metálica/Material compuesto polimérico) con el fin de aprovechar las propiedades mecánicas de cada uno y lograr un mejor rendimiento funcional. Sin embargo, la unión de estos materiales mediante técnicas adhesivas o térmicas requiere una preparación superficial adecuada, especialmente en el caso de aleaciones metálicas, para garantizar una alta calidad de unión. Para abordar esta problemática, se han investigado diversas tecnologías de mecanizado capaces de cortar simultáneamente ambos materiales sin generar separaciones o defectos en la interfaz. En este contexto, se presentan los resultados desarrollados en las siguientes líneas de investigación:

• Una comparativa de tecnologías no convencionales (Texturizado Láser, Granallado y el Corte por chorro de agua con abrasivo) para llevar a cabo operaciones de texturizado y modificación superficial. En función de la tecnología y los parámetros seleccionados se ha determinado el tipo de superficie obtenida (carácter hidrofílico o hidrófobo) mediante el cálculo de la energía libre superficial y ensayos de mojabilidad.

• Optimización de la tecnología de corte por chorro de agua como una operación de texturizado en aleaciones de aluminio 2024 de espesor reducido. Se establece la relación entre la estrategia de texturizado y los parámetros que gobiernan el proceso con la calidad final de la superficie obtenida. 

• Evaluación y optimización del mecanizado por chorro de agua con abrasivo en estructuras híbridas compuestas por aleaciones metálicas y materiales compuestos poliméricos. Se analiza la influencia del orden de apilamiento de los materiales y los parámetros de mecanizado en la aparición de defectos microgeométricos (calidad superficial) y macrogeométricos (ángulo de conicidad).

25/05/2023, Salón de Grados B

11:00-12:00

César Hibert

Estudiante de Maestría en Ingeniería de Manufactura del Instituto Politécnico Nacional de México.

Estudio numérico del arrastre de un cuerpo romo para la manufactura de un drón submarino aplicado a la exploración de cenote

El desarrollo de los drones submarinos ha tenido un crecimiento acelerado en los últimos años. Esto ha cambiado la manera en que se realizan diversas tareas en el fondo de cualquier cuerpo de agua, pues se ha alcanzado un amplio rango de aplicaciones y utilidades. Sin embargo, aún no se logran importantes avances en aspectos relevantes al momento de diseñarlos y manufacturarlos; uno de los cuales es conocer la geometría óptima que pueden tener para mejorar las condiciones de arrastre y así optimizar las condiciones de operación para el estudio e investigación dentro del área de la espeleología la cual se ha destinado el diseño de este dispositivo. En este sentido, el objetivo de esta investigación es determinar cuál es la forma geométrica óptima para la manufactura de un dron submarino a través del modelado matemático de cuerpos Romos, que incremente su autonomía, en particular la distancia de despliegue y su velocidad de recorrido. Lo anterior redunda en el mejoramiento de la geometría y eficiencia en torno a el coeficiente arrastre.

10/05/2023, Salón de Grados B

11:00-12:00

Manuel Lorite Díez

Juan de la Cierva, Universidad de Granada

Blunt body drag reduction by adaptative flexible flaps 

In this talk, flexibly-hinged rigid flaps are analysed as an adaptive and efficient drag reduction strategy in the context of 2D/3D blunt based bodies.

One the one hand, a more fundamental experimental and numerical study [1] has been carried out to test those flaps in a D-shaped body under aligned and cross flow conditions. In that sense, we vary the torsional stiffness of the hinge system to analyse the fluid-structure interaction problem that arises. The results show that, for the parameters considered, the plates undergo an inwards quasi-static, self-adaptive deflection, which is symmetric at aligned conditions and asymmetric for crosswind arrangements. This progressive streamlining of the body trailing edge translates into significant mean drag reduction up to 19 % with respect to reference static plates configuration.

On the other hand, a more applied study [2] employs a simplified model of a road vehicle, as the square-back Ahmed body, in wind tunnel tests to assess the performance of two lateral flexibly-hinged rigid flaps in fully 3D conditions. The employed system restricts the motion of the plates to a rotary displacement. We perform force and pressure measurements to quantify the variations of the drag and the base pressure coefficients while laser displacement sensors are used to obtain the angular flaps motion. Results show that the hinged plates decrease the drag coefficient of the original body efficiently in aligned/non aligned conditions contrary to the effect of fixed rigid flaps. Additionally, hinged flaps are shown to interact with the Reflectional-Symmetry-Breaking (RSB) modes, typically present in the wake of three-dimensional bodies, describing a new fluid-structure interaction phenomena involving these modes.

[1] García-Baena, C., Camacho-Sánchez, J. M., Lorite-Díez, M., Gutiérrez-Montes, C., & Jiménez-González, J. I. (2023). Drag reduction on a blunt body by self-adaption of rear flexibly hinged flaps. Journal of Fluids and Structures, 118, 103854.

[2] Camacho-Sánchez, J. M., Lorite-Díez, M., Jiménez-González, J. I., Cadot O. & Martínez-Bazán, Carlos (2023). Experimental study on the effect of adaptive flaps on the aerodynamics of an Ahmed body. Physical Review Fluids (in press).

Figure 1. Sketch of the experimental set-up (left) and detail of the flexibly-hinged flap system (right) from [2].

17/04/2023, Salón de Grados B

11:00-12:00

Daniel Baños Chetyrkin

Senior Robotics Automation Engineer, Linde Material Handling.

Intralogistics for Industry 4.0: Robotic Navigation

Due to increased investments in the Industry 4.0 revolution, Europe has become the most prominent industrial automation adopter. That concept has compelled industries to go digital with their supply chains. The European intralogistics automation market is expected to grow at a high CAGR of 11.6%. The global intralogistics market is predicted to climb from a market valuation of US$ 18.94 billion in 2022 to US$ 75.36 billion by the end of 2032.

All this creates an ideal environment for the development of different solutions applying the most modern technologies. Such as software powered by  Artificial Intelligence, automated storage systems, autonomous robots. This allows the development of different technologies and solutions. This talk will review different types of AGVs and AMRs and their uses in the industry. It will also show different types of navigation that are implemented (SLAM, reflectors, mixed,etc).

As engineers, it is a great opportunity to develop our career in this growing sector. KION Group is one of the largest groups of Intralogistics solutions and an introduction to what it is like to work as an Installation Engineer in a multinational group will be included.

24/01/2023, Salón de Grados B

11:00-12:00

Manuel Garrido

Contratado predoctoral, Mecánica de Fluidos UMA. 

Higher order dynamic mode decomposition as a data-based tool for the characterization of wingtip vortices

Simple aerodynamic configurations, even under modest conditions, can exhibit a wide range of complex flows which are characterized by spatial and temporal features. The description of the implicit coherent structures is crucial to our understanding of fluid-dynamical behaviour and its modeling and control. Particularly, the decay of trailing vortices is a fundamental problem in fluid mechanics and constitutes the basis of control applications that intent to alleviate the wake hazard. The formation of these trailing vortices is caused by the finite length of three-dimensional aerodynamic profiles, which appear in applications such as sailing hydrofoils, turbomachinery, or aircraft. Our main interest is in the latter, where a persistent and highly rotating axial flow is generated during takeoff and landing operations in airport runways.

In the present study, we use a recently developed modal-decomposition technique, Higher order dynamic mode decomposition (HODMD), to identify the governing dynamics in an experimental trailing vortex. HODMD is a factorization and dimensionality reduction technique for data sequences, which efficiently extracts coherent structures and reduces complex evolution processes to their dominant features and essential components. The fluid flow data used in the study is obtained from the experiments performed in a water-tunnel at chord-based Reynolds number Re=4×104 using Stereoscopic Particle Image Velocimetry measurements over a downstream range of 36 chords. The extracted higher order dynamic modes of the streamwise vorticity can be used to describe the underlying physical mechanisms captured in the data sequence, showing that the decay is well approximated by at most three modes in each part of the wake. Additionally, the application of HODMD provides evidence for the existence of several instabilities after the vortex roll up beyond about 6.5 chords.

Referencias:

P. Gutierrez-Castillo, M. Garrido-Martin, T. Bölle, J. H. García-Ortiz, J. Aguilar-Cabello, and C. del Pino , "Higher order dynamic mode decomposition of an experimental trailing vortex", Physics of Fluids 34, 107116 (2022).

C. del Pino, J. Lopez-Alonso, L. Parras, and R. Fernandez-Feria, “Dynamics of the wing-tip vortex in the near field of a NACA 0012 aerofoil,” Aeronaut. J. 115, 229–239 (2011).

S. Le Clainche and J. M. Vega, “Higher order dynamic mode decomposition,” SIAM J. Appl. Dyn. Syst. 16, 882–925 (2017).

22/12/2022, Salón de Grados B

11:00-12:00

Adrián Domínguez-Vázquez 

Visiting Professor. Equipo de Propulsión Espacial y Plasmas. Universidad Carlos III de Madrid. 

On numerical simulations of Hall effect thrusters

This talk presents the latest advances on the numerical simulation of Hall effect thruster (HET) prototypes for space missions carried out by EP2 research group at Universidad Carlos III de Madrid (UC3M). 

The main characteristics of two different simulation models for HET discharges are presented. The first one, named HYPHEN, implements an advanced 2D axisymmetric hybrid particle-in-cell (PIC)/fluid model to simulate the chamber and near plume region of a HET [1,2]. It has been recently upgraded for the simulation of new high-efficiency magnetically-shielded (MS) HET prototypes [3]. It provides a complete 2D characterization of the plasma discharge, including 2D maps of plasma currents and estimations of plasma losses to walls, which permit to assess thruster performance and lifetime. Simulation results for SITAEL’s HT5k and SAFRAN’s PPS5000 prototypes under current development are compared. Main results from a recent data-driven analysis applied to a HET discharge are presented [4]. Furthermore, on-going results for a modulated HET discharge are discussed.

The second simulation code corresponds to a full PIC 1D radial model of the acceleration region of a HET discharge devoted to the analysis of the plasma-wall interaction phenomenon and its effects on the radial dynamics of the electron population [5,6]. In a HET discharge, plasma collisionality is low and plasma interaction with the thruster walls is strong, including the emission of secondary electrons from the walls. Both facts make the electron velocity distribution function (VDF) deviate from a maxwellian one, thus affecting the pressure tensor, the heat flux and the fluxes of particles and energy deposited to the walls. The kinetic solution provided by the full PIC radial model allows to evaluate these effects and to improve HYPHEN estimates of electron particle and energy fluxes to walls through scaling laws retaining relevant kinetic effects. Main results from two recent studies for a purely radial magnetic field [7] and for an oblique magnetic field [8] are presented. On going work is extending this 1D radial model to a 2D axial-radial one.

References:

[1] Domínguez-Vázquez, A., Axisymmetric simulation codes for Hall effect thrusters and plasma plumes , Ph.D. thesis, Universidad Carlos III de Madrid, Leganés, Spain, 2019. 

[2] Domínguez-Vázquez, A., Zhou, J., Fajardo, P., and Ahedo, E., “Analysis of the plasma discharge in a Hall thruster via a hybrid 2D code,” 36th International Electric Propulsion Conference, No. IEPC-2019-579, Electric Rocket Propulsion Society, Vienna, Austria, 2019. 

[3] Perales-Díaz, J., Domínguez-Vázquez, A., Fajardo, P., Ahedo, E., Faraji, F., Reza, M., and Andreussi, T., “Hybrid plasma simulations of the HT5k thruster,” ExB Plasmas Workshop, Young researchers ”poster” mini-session, Madrid, Spain, February 16-18, 2022. 

[4] Maddaloni, D., Domínguez-Vázquez, A., Terragni, F., and Merino, M., “Data-driven analysis of oscillations in Hall thruster simulations,” Plasma Sources Science and Technology, Vol. 31, No. 4, apr 2022, pp. 045026. 

[5] Domínguez-Vázquez, A., Taccogna, F., and Ahedo, E., “Particle modeling of radial electron dynamics in a controlled discharge of a Hall thruster,” Plasma Sources Science and Technology, Vol. 27, No. 6, 2018, pp. 064006. 

[6] Domínguez-Vázquez, A., Taccogna, F., Fajardo, P., and Ahedo, E., “Parametric study of the radial plasmawall interaction in a Hall thruster,” Journal of Physics D: Applied Physics, Vol. 52, No. 47, 2019, pp. 474003.

 [7] Marín-Cebrián, A., Domínguez-Vázquez, A., Fajardo, P., and Ahedo, E., “Macroscopic plasma analysis from 1D-radial kinetic results of a Hall thruster discharge,” Plasma Sources Science and Technology, Vol. 30, No. 11, November 2021, pp. 115011. 

[8] Marín-Cebrián, A., Domínguez-Vázquez, A., Fajardo, P., and Ahedo, E., “Kinetic plasma dynamics in a radial model of a Hall thruster with a curved magnetic field,” Plasma Sources Science and Technology, Vol. 31, No. 11, nov 2022, pp. 115003.

20/12/2022, Salón de Grados B

11:00-12:00

Daniel Domínguez-Vázquez 

PhD student. Department of Aerospace Engineering. San Diego State University.

"A comprehensive analysis of Eulerian-Lagrangian descriptions of particle-laden flows with random forcing"

Multiphase flows in which a disperse phase composed of particles, droplet or bubbles interacts with a carrier flow are present in many natural and industrial processes such as volcano eruptions, fuel injection in scramjets or dispersion of pollutants into the atmosphere among others. The multiscale character of such flows has been the main driver in the last decades for many reduced models to be derived. These models reduce the complexity and computational cost of such models by introducing physical assumptions. The so-called Point-Particle-In-Cell (PSIC) or point-particle method, is a well known model that assumes the particles to be volumeless singular points. These particles are traced along their Lagrangian path and their influence is coupled with the carrier phase via singular source terms. The forcing of such particles however, is typically not known with certainty for most of the physical situations. In fact, the common practice is to use empirical or data-driven correlations to correct the scarce analytical solutions available in the literature, as for example the Stokes’ law for small spherical particles with smooth surface in a laminar flows in the absence of particle-particle interactions. This empiricism introduced in the point-particle model has to be taken into account in order to quantify the accuracy of the point-particle method and be able to detect regimes where the forcing should be prescribed more accurately. In this talk, I will walk you through a comprehensive review of the different models of particle-laden flows described in Eulerian-Lagrangian frame and will introduce a new framework to describe such flows when the forcing is considered random (not certain). This framework, allows to carry out systematic uncertainty quantification and the reconstruction of the forcing by measured data from experiments and/or high-fidelity simulations. Probability density function methods, method of moments and Monte Carlo techniques will be discussed, as well as a learning technique based on the adjoint formulation of the PSIC method combined with an optimization algorithm that allows to reconstruct the forcing from data.

16/12/2022, Aulas de Máster, 0.24

11:00-12:00

Alfredo Pinelli.

Professor of Fluid Simulation. School of Science & Technology, Department of Engineering. City, University of London. 

On the genesis of different regimes in canopy Flows

Surfaces of anchored filamentous layers exposed to fluid flows are commonly found in nature and in man-made environments. A few examples are: crop fields where the exchange of mass, heat, radiation and momentum between the canopy layer and the environment surrounding regulates photosynthesis processes; ciliated walls in organs participating in a number of physiological processes like locomotion, digestion, circulation, respiration and reproduction; urban canopies where the interaction with the atmospheric boundary layer determines the local micro-climate. In this talk, after a review of the main parameters that govern the flow regime taking place inside and outside the canopy, and the numerical methods applied for carrying out resolved canopies simulations, we will describe in detail the flow structure in both straight and inclined canopies occurring in different regimes and the coupled interaction between the outer turbulent flow and the inner porous-like medium. 

Finally, an overview of applications and the possibility of designing canopies and walls covered with textured surfaces, for specific technological purposes will be discussed.

Bio A. Pinelli

Alfredo Pinelli is a professor of fluid mechanics at City, University of London. He graduated in aeronautical engineering at Milan Polytechnic. He received his PhD in applied mathematics from EPFL (École Polytechnique Fédérale de Lausanne, Switzerland) and holds a diploma course in fluid dynamics from the von Karman Institute of fluid dynamics. He has spent more than 4 years as an associate researcher at the ETSIA Aerónauticos in Madrid, working with Prof. Jiménez on wall-bounded turbulent flows. He has been an associate professor at both UCIIIM and at Complutense University in Madrid, and before being appointed as chair of fluid mechanics at City, he led for 10 years the group of modelling and simulations at CIEMAT. He is a fellow of the Royal Aeronautical Society and Associate Dean for Research at the School of Science and Technology of City University. His main research interests are (but are not limited to) numerical fluid mechanics, turbulent boundary layers, and flows over complex surfaces. He has authored more than 60 peer-reviewed articles, including one of the most cited papers in the journal of fluid mechanics.

15/12/2022, Aulas de Máster, 0.24

10:00-11:00

Javier Alaminos

Postdoctoral Scholar.  Mechanical and Aerospace Engineering, University of California San Diego.

"The description of buoyancy effects on the dispersion of drugs released intrathecally in the spinal canal"

The transport of drugs along the spinal canal can be delivered by direct injection into the cerebrospinal fluid (CSF) that fills the intrathecal space surrounding the spinal cord. The analysis must account for the motion of the CSF, which moves under the action of the pressure oscillations induced by the cardiac and respiratory cycles. The resulting oscillatory velocity is known to have a time-averaged Lagrangian component, given by the sum of the steady-streaming and Stokes-drift velocities, which largely determines the drug dispersion rate along the canal. Attention is focused here on effects of buoyancy-induced motion. Although the relative density differences between the drug and the CSF are typically very small---on the order of 1/1000 for drugs diluted with water and 1/100 for drugs diluted with dextrose---the associated Richardson numbers are shown to be of order unity, so that the resulting buoyancy-induced velocities are comparable to those of steady streaming. Consequently, the slow time-averaged motion of the fluid particles is coupled with the transport of the drug, resulting in a slowly evolving steady-streaming problem that can be treated with two-time scale methods. The analysis produces a nonlinear transport equation that is used to illustrate effects of buoyancy in medical procedures involving drugs that are slightly denser or slightly lighter than the carrier fluid.

23/11/2022, Salón de Grados B

11:00-12:00

Eduardo Durán Venegas

Postdoctoral Researcher PAIDI. Departamento de Mecánica de Estructuras e Ingeniería Hidráulica, Área de Mecánica de Fluidos Universidad de Granada. 

"Computational fluid dynamics to predict cardiac diseases: the importance of uncertainty quantification"

Cardiovascular diseases are a leading cause of mortality worldwide. For instance, ischemic stroke, one of the most common cardiac diseases, affects over 18 million people yearly. In particular, these strokes are highly related to thrombi generated in the cardiac chambers, whose anatomy varies significantly among patients, affecting blood behavior. However, despite this variability, current medical procedures to estimate the risk of ischemic stroke or other cardiac diseases are based on population demographics and do not consider patient-specific information about hemodynamics. In this sense, computational fluid dynamics (CFD) based on patient-specific medical images can provide useful information to predict cardiac diseases, investigating different aspects of heart hemodynamics, e.g., blood stagnation, non-Newtonian effects inside the cardiac chambers, or the influence of vein flow rates. Recent studies have provided helpful guidance for setting up models and boundary conditions that precisely reproduce each patient’s hemodynamics in a specific physiological state. However, these physiological circumstances can vary significantly between patients or during a patient’s daily life. In this talk, we analyze cardiac flows through CFD simulations and study how different uncertainty sources can affect heart hemodynamics.

5/07/2022, Aulas de Máster, 0.24

11:00-12:00

David Rival

Associate Professor, Department of Mechanical Engineering, Queen's University (Canada)

"Pushing the boundaries of in situ Lagrangian flow measurements"

The potential for clouds of distributed, Lagrangian sensors in complex environmental flows, when coupled with network-science tools, offers a myriad of fresh opportunities to characterize key transport processes critical to modeling (and adapting to) climate change. For sake of illustration, both passive (e.g. drifting seeds) as well as active (flying/swimming) sensing platforms, are described here. Some examples of optimal sensing in flying/swimming, based on proprioception, will be touched on before embarking on a description of a novel passive technique using nothing other than air-filled soap bubbles to follow the flow. Here, we show how a single-camera perspective can be used to track centimeter-sized soap bubbles in three dimensions by not only evaluating the bubble-center location but also the bubble-image size itself. Of course with such Lagrangian measurements come challenges associated with identifying flow features with inherently sparse data. Existing approaches, based on graph theory, will be reviewed before a new technique using multi-scale recurrence networks will be tested on a series of canonical problems.

Bio:

Dr. Rival leads a large research group at the interfaces between experimental fluid dynamics, data assimilation, network science and bio-inspiration. In 2020, Dr. Rival was awarded a one-year Alexander von Humboldt research fellowship to conduct research on advanced sensing techniques in Munich. Prior to joining Queen’s, Dr. Rival completed his doctoral studies on the aerodynamics of dragonfly flight at TU Darmstadt, worked as a postdoctoral associate at MIT on shape morphing in nature, and held a research chair on atmospheric sensing at the University of Calgary. The lab is involved in a number of international research collaborations sponsored by, for instance, AFOSR and NATO, and has been featured on David Suzuki’s The Nature of Things as well as on the Discovery Channel’s Daily Planet show.

27/06/2022, Salón de Grados B , E.I.I.

11:00-12:00

Amal Haraketi

ERASMUS+ Master Thesis Student, ESAT University (Tunisia) 

"Study of aerodynamic coefficients on deformed wings using numerical simulations"

This work analyzes the results obtained with numerical simulations using ANSYS. on geometries of deformed and undeformed wings with different models of turbulence and boundary conditions. The results show the influence of the deformation and aspect ratio on the lift and drag coefficients.

13/05/2022, Salón de Grados B , E.I.I.

11:00-12:00

Jorge Aranda

Becario FPI, Área de Mecánica de Fluidos de Málaga

"Liquid Metal Electro-dripping"

The atomization modes of capillary flows under the action of an electric field have been classified throughout over a century. Among them, the periodic electric dripping and electric micro-dripping are an easy way to generate monodisperse droplets in a rather broad size range, from tens of microns up to millimeters [1]. In the present study, we atomize a molten metal at room temperature, Gallium-Indium eutectic (eGaIn), in a periodic electro-dripping mode to generate monodisperse droplets in the hundreds of microns size range. The final objective is the use of such charged molten metal droplets to form 3D structures upon solidification. We report on the measurement and characterization of the ejection frequency and droplet size, and their dependence on the controlling parameters, liquid flow rate and applied voltage.

[1] J. Rosell-Llompart, J. Grifoll, and I. G. Loscertales, Electrosprays in the cone-jet mode: From taylor cone formation to spray development, Journal of Aerosol Science 125, 2 (2018).

02/06/2022, Salón de Grados B , E.I.I.

10:00-11:00

Patrice Le Gal 

Directeur de Recherche, Aix-Marseille Univ, CNRS, Centrale Marseille, IRPHE, France 

"Dynamics of a Ludion in a Stratified Sea: when a diver becomes a swimmer"

We describe and model experimental results on the dynamics of a ”ludion” - a neutrally buoyant body – immersed in a layer of stably stratified salt water. By oscillating a piston inside a cylinder communicating with a vessel containing the stratified layer of salt water, it is easy to periodically vary the hydrostatic pressure of the fluid. The ludion or Cartesian diver, initially positioned at its equilibrium height and free to move horizontally, can then oscillate vertically when forced by the pressure oscillations. Depending on the ratio of the forcing frequency to the Brunt-Väisälä frequency N of the stratified fluid, the ludion can emit its own internal gravity waves that we measure by Particle Image Velocimetry. Our experimental results describe first the resonance of the vertical motions of the ludion when excited at different frequencies. A theoretical oscillator model is then derived taking into account added mass and added friction coefficients and its predictions are compared to the experimental data. Then, for the larger oscillation amplitudes, we observe and describe a bifurcation  towards free horizontal swimming. For forcing frequencies close to N, chaotic trajectories are recorded. The statistical analysis of this dynamics is in progress but already suggests the existence of an underlying non equilibrium thermodynamics with even possible ”condensations” of ludions in pairs or in triplets when several ludions are introduced in the container. Finally, we also observed that the ludion can interact with its own internal gravity wave field and possibly become trapped in the container gravity eigenmodes. However, it  seems that, contrary to the surface waves associated with Couder walkers, the internal waves are not the principal cause of the horizontal swimming. This does not however, exclude possible hydrodynamic quantum analogies to be explored in the future.

13/05/2022, Salón de Grados B , E.I.I.

11:00-12:00

José Manuel Gordillo Arias de Saavedra

Catedrático del departamento de Ingeniería Aeroespacial y Mecánica de Fluidos, Universidad de Sevilla

"The initial impact of drops cushioned by an air or vapor layer with applications to the dynamic Leidenfrost regime"

This work is devoted to the study of the conditions under which a drop directed normally towards a superheated or isothermal smooth substrate prevents the initial contact with the solid by skating over a micrometer-sized vapor or air layer. The results have been obtained analysing the gas flow at the spatio-temporal region where the maximum liquid pressure is attained, which is also where and when the minimum values of the film thickness are reached. For the common case in which  We St -1/6 ≥1, where We = ρl U2 R/γ and St = ρl U R / ηa denote, respectively, the Weber and Stokes numbers, we find that capillary effects are negligible and the ratio between the minimum film thickness and the local drop radius of curvature is hm/R α St -7/6, with ρl , γ, ηa, U and R indicating the liquid density, the interfacial tension coefficient, the gas viscosity, the impact velocity and the drop radius, respectively. In contrast, when  We St -1/6 ≤ 1, capillary effects can no longer be neglected and hm/R α We -1/3 St -10/9. The predicted values of the minimum film thickness are compared with published experimental data, finding good agreement between predictions and measurements for the cases of both isothermal and superheated substrates. In addition, using mass conservation, we have also deduced an equation providing the minimum value of the substrate temperature for which a cylindrical central vapor bubble of constant height hd/R α St-2/3, with hd >> hm grows radially at the wetting velocity deduced in [1]. The predicted values are in good agreement with the dynamic Leidenfrost temperatures reported by [2]."

[1] Riboux, G. & Gordillo, J. M. 2014 Experiments of drops impacting a smooth solid surface: A model of the critical impact speed for drop splashing. Phys. Rev. Lett. 113, 024507. 

[2] Shirota, Minori, van Limbeek, Michiel A. J., Sun, Chao, Prosperetti, Andrea & Lohse, Detlef 2016 Dynamic leidenfrost effect: Relevant time and length scales. Phys.

Rev. Lett. 116, 064501. 

6/05/2022, Salón de Grados B , E.I.I.

11:00-12:00

José Manuel López Alonso

JdC Incorporación, Universidad Politécnica de Cataluña, Dpto. Física Aplicada. 

"Elasto-inertial turbulence: the missing link to explain the mysterious MDR limit of polymer drag reduction "

The drag of turbulent flows can be drastically decreased by addition of small amounts of high molecular weight polymers. While drag reduction initially increases with polymer concentration, it eventually saturates to what is known as the maximum drag reduction (MDR) limit. Surprisingly, MDR is insensitivity to the polymers and solvent used, a feature that is generally attributed to the dynamics being reduced to a marginal yet persistent state of subdued turbulent motion. In this talk, I will present a body of numerical and experimental evidence that challenges this commonly accepted view and suggests that the universality of MDR is instead connected to a new type of turbulence, dubbed elasto-inertial turbulence (EIT), which fully replaces Newtonian-like turbulence in viscoelastic parallel shear flows [1][2]. Distinctive structural and statistical features of EIT as compared with ordinary Newtonian turbulence will be discussed. While it is known that EIT arises from a viscoelastic flow instability (VFI), the precise nature of this instability is still unclear. I will discuss potential mechanisms that might cause this VFI and show recent experiments by our group suggesting that EIT might be the result of a supercritical transition scenario [3]. Finally, if the time permits, I will also discuss a novel turbulent drag reduction strategy based on flow rate control which I have recently put forwards in collaboration with researchers of Austria and India. 

[1]  "Exceeding the asymptotic limit of polymer drag reduction". GH Choueiri, JM Lopez, B Hof.

Physical review letters 120 (12), 124501.

[2] "Dynamics of viscoelastic pipe flow at low Reynolds numbers in the maximum drag reduction limit". JM Lopez, G Choueiri, B Hof. Journal of Fluid Mechanics 874, 699-719.

[3] "Experimental observation of the origin and structure of elastoinertial turbulence". GH Choueiri, JM Lopez, A Varshney, S Sankar, B Hof. Proceedings of the National Academy of Sciences 118 (45).

4/05/2022, Salón de Grados B , E.I.I.

11:00-12:00

Javier Rivero

Contratado postdoctoral, Universidad de Málaga, Área de Mecánica de Fluidos. 

"Surface tension in microfluidics: numerical methods and applications"

Surface tension plays an important role in the dynamics of two-phase flows below the millimeter scale. We are exploring its formulation and how to numerically deal with deformable domains without changes of topology. Two novel numerical approaches are proposed: (i) an alternative for the boundary conditions of the Arbitrary Lagrangian-Eulerian method that allows a better control of the mesh distortion and (ii) a perturbation method that is applicable in complex geometries and unstructured meshes. Then, these approaches are applied to some phenomena of interest in microfluidics such as inertial/capillary migration, liquid bridges, droplets production and electrified drops vibration.

26/04/2022, Salón de Grados B , E.I.I.

11:00-12:00

José Carlos Sánchez Garrido

Profesor Titular de Universidad, Departamento de Física Aplicada II, Universidad de Málaga

“Environmental control of fish population cycles in climate-to-fish ocean models”

Small pelagic fish represent up to 50% of the total landing of marine food catch and provide the forage for their multiple predators, which include a broad variety of larger fish, sea birds, and sea mammals. Situated near the base of the food web, small pelagic fish represent a major link between lower and upper trophic levels and thereby play a key role in sustaining entire marine ecosystem. These facts, along with their great commercial value (e.g., sardine and anchovy) and strong sensitivity to environmental changes, make it particularly necessary to better understand their population dynamics, especially in response to the present scenario of climate change.  

End-to-end ecosystem models, combining models of ocean circulation and physics, lower trophic levels (nutrient, phytoplankton, and zooplankton), and an upper trophic level representing fish bioenergetics and behavior, are comprehensive numerical tools designed to address these questions. As computing power is ever increasing, end-to-end models are now gaining in complexity and realism. Among other features, state-of-the-art models allow for feedback between all components of the ecosystem (fully coupled models), run over the same three-dimensional computational grid, and afford multidecadal mesoscale eddy-resolving simulations of large marine ecosystem.

In this talk, I will show how a climate-to-fish model can be used to gain insights into the population dynamics of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) in the Canary Current upwelling ecosystem. I will present analysis techniques to unravel the link between climate, environmental (i.e., biochemistry and physical) and the simulated biological variability. I will also compare our results with previous modeling efforts made in the California Current (Fiechter et al. 2015), highlighting the physical and biological processes giving rise to qualitatively different variability of anchovy and sardine populations in these two major eastern boundary upwelling ecosystems.

1/04/2022, Salón de Grados B , E.I.I.

11:00-12:00

Alejandro Millán-Merino

Post Dotorant in Aix Marseille Univ, CNRS, Centrale Marseille, M2P2, Marseille (France)

"Theoretical and numerical analysis of isolated ethanol droplets: evaporation and combustion"

Net-zero emissions biofuels are those in which the total amount of CO2 produced in the combustion process is compensated by the CO2 absorption in the production process (farming or electrocatalysis). Amount them, ethanol has been extensively used in engines to lower Green House Gas emissions. In most practical applications, the fuel is injected as a spray inside the combustion chamber, forming a cloud of small droplets that evaporates, first, mixing with the surrounding ambient air before the flame is formed either by autoignition or with the help of an external source of heat.

At present, ethanol content in fuel mixtures is typically lower than 15% in volume, because of technical problems. As ethanol is a hydrophilic substance, significant amounts of water can be absorbed by a tank of ethanol changing the combustion properties of the fuel. In this work, using an order-of-magnitude analysis and detailed unsteady one-dimensional simulations, evaporation and combustion of ethanol droplets immersed in a hot and humid atmosphere will be presented. Additionally, the effects of the droplet water content and the ambient moisture on the vaporization rate and the autoignition time will be analyzed.

30/03/2022, Salón de Grados B , E.I.I.

11:00-12:00

Francisco Marqués

Catedrático de Física Aplicada en la Universidad Politécnica de Cataluña

"Plumas térmicas: sistemas dinámicos y simulación numérica"

Las plumas térmicas son muy comunes en la naturaleza, y aparecen también en diversos fenómenos industriales y de laboratorio. Su análisis se ha centrado normalmente en el estudio de plumas turbulentas, pero para la comprensión de los mecanismos físicos responsables de su estructura es importante analizar las etapas de su formación desde un estado inicial laminar a la turbulencia, pasando por una serie de bifurcaciones que van conformando una estructura cada vez más compleja. En este análisis de la transición a la turbulencia juega un papel determinante la teoría de sistemas dinámicos, que nos dice el tipo de inestabilidades y bifurcaciones que pueden tener lugar. Presentaremos en este trabajo detalladas simulaciones numéricas de las ecuaciones de Navier-Stokes, que combinadas con la teoría de sistemas dinámicos y el análisis de las simetrías del sistema, permiten entender los mencionados procesos de transición.

22/03/2022, Salón de Grados B , E.I.I.

11:00-12:00

Francisco Javier Granados Ortiz

Postdoc Junta de Andalucía, Universidad de Málaga, Área de Mecánica de Fluidos. 

"CFD modelling under uncertainty"

Nowadays is inconceivable the development of new designs in aero/hydrodynamic applications without the use of Computational Fluid Dynamics (CFD). These numerical tools reduce the costs to develop improved designs in contrast to a costly iterative manufacturing plus experimental testing. However, the accuracy of CFD simulations is often doubtful due to the omission of existing sources of uncertainty. To include uncertainty estimates in these simulations often requires important computational costs. An example is classic Monte-Carlo sampling, which is unaffordable because of the requirement of hundred/thousands of CFD simulations. In this talk, classical sources of uncertainty will be presented, as well as methods to account for the contribution of several random inputs in a probabilistic framework. Successful designs developed via CFD will be also presented, together with discussion of the challenges faced during its development.The dynamics of vortex meandering – review and recent progress"

25/11/2021, Salón de Grados B , E.I.I.

11:00-12:00

Tobias Bölle

Postdoctoral Researcher, Institut für Physik der Atmosphäre  (DLR), Germany. 

"The dynamics of vortex meandering – review and recent progress"

Vortex meandering – the seemingly random lateral deflection of vortices – is considered to be the main manifestation of wake-vortex unsteadiness. Comprehension of its governing dynamics is expected to indicate possible ways of vortex alleviation. Thus, decreasing the hazard of wake encounters and potentially controlling the formation of contrails. However, despite its universal observation in experiments since the 1970s, the dynamics of vortex meandering remains puzzling in its essential aspects as of today. In this talk, we review the main characteristics of the phenomenon, showing that meandering is universally associated with three clear signatures of evolution in time and frequency space. We then present recent progress made in the understanding of these three main features using an experimental database in conjunction with a theoretical model. In particular, in response to an ongoing controversy,  by appeal to time-series analysis we find that the phenomenon is neither stochastic nor associated with a single frequency. On the basis of our combined theoretical-experimental analysis, we propose the mother–daughter mechanism of Boberg & Brosa (Z. Naturforsch. A 43.8-9 (1988): 697-726) to govern the energy budget.

10/10/2019, Salón de Grados B , E.I.I.

11:00-12:00

Thomas Leweke

Senior Researcher (Directeur de Recherche), IRPHE, CNRS, Marseille, France

“Pairing instability and Vortex Ring State in the wake of a rotor”

The wake of a rotor, such as the one of a horizontal axis wind turbine, a helicopter or a marine propeller, is characterized by the presence of concentrated vortices, which are generated at the tips of the rotor blades as a consequence of the lift they produce, and which take on the geometry of a system of interlaced helices. In this presentation, experimental results concerning two phenomena occurring in helical rotor wakes are  shown: a long-wave displacement instability and the transition to the so-called Vortex Ring State.

Single or multiple helical vortices are known to be unstable with respect to displacement perturbations, whose wavelengths are large compared to the characteristic vortex core size; they are characterized by a local pairing of consecutive helix loops. Experiments were carried out in a water channel using small-scale one- or two-bladed rotors to generate helical vortex systems. Various modes of the pairing instability could be excited by suitable perturbations of the rotor rotation, and their characteristics and growth rates were determined from dye visualizations and Particle Image Velocimetry. A link can be established between this phenomenon and the well-known pairing instability of an infinite array of point vortices, representing straight parallel vortices.

For rotors operating in the regime corresponding to helicopter flight, a transition of the wake to a state where the tip vortices are captured in a large-scale vortex-ring structure in the rotor plane is found for descending flight. It represents a well-known hazard for helicopter flight, associated with a rapid loss of lift. Extensive water tunnel measurements on rotors in normal and yawed conditions, corresponding to combinations of vertical and forward flight of a helicopter, showed that this Vortex Ring State is accompanied by low-frequency fluctuations of the rotor wake. 

Visualizations, measurements and interpretations of the observed phenomena are presented, and the relevance for applications are discussed.

Biography

Thomas Leweke is a Senior Researcher of the French National Centre for Scientific Research (CNRS), working at the Institut de Recherche sur les Phénomènes Hors Equilibre (IRPHE) in Marseille, France. He graduated in Physics from the RWTH Aachen University in Germany in 1991 and obtained his PhD in Fluid Mechanics from the Université de Provence (today Aix-Marseille Université) in Marseille in 1994. He then worked as a postdoctoral researcher at Cornell University, before being employed by CNRS and returning to Marseille in 1996. His research in fluid mechanics concerns experimental studies of fundamental phenomena in the fields of bluff body wake dynamics and vortex interactions, as well as separated flows. In recent years, his work has focussed on the flow around rotors, in collaboration with Airbus Helicopters and the Scandinavian wind energy community. He is an associate editor of the Journal of Fluids and Structures and of the Journal of Visualization.

10/06/2019, Salón de Grados B , E.I.I.

11:00-12:00

Eduardo Durán-Venegas

Attachés temporaires d’Enseignement et de Recherche, Institute de Recherche sur les Phenomenes Hors Equilibre, Marsella. 

"Modeling of Flexible Rotor Blades"

Rotors have been historically developed for harvesting and propulsion. For wind turbines and helicopters, decades of research have been done to optimize their design. For recent applications, such as drones, no such a research effort has been made. The high flexibility of the rotor and the different operational conditions still constitute challenging issues for their design. In this work, a coupled fluid-structure model is proposed, taking into account the flexibility of the blades in non-conventional operational conditions.

The model is sufficiently simple and robust to permit extensive parameter studies. It includes a model for  the wake, a model for the flexible rotor structure and the coupling. The wake is described using vortex filaments. Two different wake models are considered: a classical Joukowski model, where two vortices are emitted per blade, one at the tip and one at the axis, and a generalized Joukowski model where the axial vortex is replaced by a hub vortex emitted away from the center. For both cases, stationary wake solutions are obtained in the rotor frame for a very large range of operational conditions.

A stability analysis of the solutions derived with the classical Joukowski model is performed. A good agreement is demonstrated with the theoretical results for uniform helical filaments. The convective/absolute nature of the instability is also analysed for various operational conditions.

Stationary wake solutions are used to calculate the flow in the rotor plane. Kutta-Joukowski law and Blade Element Theory are applied to obtain the aerodynamic loads exerted on the blades. The full coupling of the rotor with its wake is first implemented for a rigid configuration. Coupled solutions are obtained for different rotors and compared to experimental and numerical data published in the literature. A good agreement is observed for most cases. Then, blade flexibility is considered using a rod model for the blade.  Various converged solutions for flexibles rotors are obtained using a classical Joukowski model for the wake. A parametric study is also performed to quantify the effects of blade elasticity on the solution.

17/01/2018, Salón de Grados B , E.I.I.

11:00-12:00

José Ignacio Jiménez- González

Profesor Ayudante Doctor, Universidad de Jaén 

“Control of three-dimensional wakes behind simplified models of blunt-based vehicles”

The flow around heavy vehicles, such as trucks is mainly characterized by a massive separation that induces the development of a strong wake behind the body and the periodic shedding of vortices. Such features result into the appearance of major fluctuating aerodynamic forces and a large drag coefficient that hinders the fuel consumption and renders such type of vehicles a major source of greenhouse gases emission. Consequently, these kinds of wakes have been extensively studied in the last decades [1] with the aim at developing new, more efficient flow-control methods or to improve the existing ones in terms of drag and flow-induced loads. Due to the geometrical complexity of vehicles, these analyses focus generally on simplified models, such as the square-back Ahmed body [2], whose wake retains the main features of three-dimensional wakes. In that sense, it has been recently shown [3] that the turbulent wake behind square-back models sustain, aside from the periodic shedding (periodic mode), a bi-stable random dynamics characterized by the intermittent switching between two horizontally deflected mirror positions (steady Reflectional Symmetry Breaking, RSB, modes). The control of such bi-stable wake asymmetry may lead to considerable drag reduction and decrease of lateral force fluctuations. Following this goal, we present experimental results from our studies on control strategies for the turbulent wake behind the Ahmed body. In particular, we first apply steady perimetric blowing at the base, focusing on the effect of increasing values of the dimensionless base flow parameter, C m , on the periodic and steady RSB modes for different perimetric blowing configurations. Thus, two general types of behaviors have been identified in terms of the drag coefficient, as the value of Cm increases. For weak blowing rates, a mass injection mechanism acts filling the recirculation bubble and increasing its length, leading to the subsequent decrease of the drag force. Eventually, at higher blowing rates, such effect is reversed and the recirculation region size reduces, leading to an increase of drag. The latter behavior, which will be denoted as momentum regime, produces important changes on steady RSB modes, translating the wake deflected position from horizontal to vertical directions for some blowing configurations. The effect of the blowing density on the aforementioned mechanisms will be also discussed, showing that a light gas reduces more efficiently the drag coefficient than heavier gases. Besides, a second passive strategy is presented, whereby curved rear cavities, designed by means of topological optimization processes, are tested on the Ahmed body for different yaw angles, showing a larger drag reduction and bi-stable dynamics mitigation than classical solutions consisting of straight cavities or flaps.

[1] H. Choi, et al. Annual Review of Fluid Mechanics 46:44-68, 2014.

[2] S. R. Ahmed et al. SAE Tech. Rep. No. 840300, 1984.

[3] M. Grandemange et al. Journal of Fluid Mechanics, 722:51-84, 2013.

Biography

José Ignacio Jiménez González is Assistant Professor at the Department of Mechanical and Mining Engineering from Universidad de Jaén, and member of the Fluid Mechanics Research Group TEP235, headed by Prof. Carlos Martínez-Bazán. He received his MSc in Mechanical Engineering (2009) and PhD (2013) from the same University. His PhD Thesis was devoted to study the stability and control of wakes behind axisymmetric bodies. Since 2013, he has partially carried out his scientific work as Invited Lecturer at the Institut de Mécanique des Fluides de Toulouse (IMFT, France), focusing on hydrodynamic stability of jets and optimal perturbation studies, and has complemented his postdoctoral training by means of several stays at Universitat Rovira i Virgili and École Nationale Supérieure de Techniques Avancées (ENSTA-ParisTech, France). He is currently leading a national research project on the stability of wakes behind three-dimensional blunt-based bodies (e.g. trucks), vortex-induced vibrations and control through passive techniques. Such project is undertaken in collaboration with researchers from University of Liverpool and ENSTA-ParisTech. He has been also recently appointed as member of the Steering Committee of the new ERCOFTAC (European Research Community on Flow, Turbulence and Combustion) Special Interest Group (SIG) on 3D Wakes.

13/12/2018, Aula 0.23 , E.I.I.

11:00-12:00

Álvaro Meseguer

Profesor Titular de Universidad, Universidad Politécnica de Barcelona 

“Understanding transition to shear fluid turbulence: computing hidden flows and beyond”

Predicting when and how a fluid in laminar motion may become turbulent is one of the most challenging (and yet unsolved) fundamental problems of classical physics. Current computational power allows for the accurate numerical simulation of fluid flows by means of CFD (Computational Fluid Dynamics) software packages. The majority of CFD codes currently used by scientists and engineers are essentially time evolution solvers (also termed as time-steppers) of the fluid that provide time integrations of the Navier-Stokes initial value problem. Therefore, classical CFD codes can only reproduce stable flows, regardless the nature of their dynamics: steady, time-periodic, almost-periodic or chaotic. In other words, current standard CFD time-stepping codes can only identify local attractors. Recent studies [2, 1] have clearly evidenced that the destabilization of many open shear flows (such as the ones appearing in pipes or channels) may be related to the presence of unstable Navier-Stokes solutions close to the stable base flow. Forecasting hydrodynamic instabilities in many fluid flows therefore requires the detection of the presence of these repelling Navier-Stokes solutions and their eventual computation. These exact Navier-Stokes flows are hidden since they are unstable and cannot be approached by standard CFD time-stepping codes. Numerical computation of these types of unstable flows is an even more challenging task, where new mathematical concepts such edge state dynamics and top-notch numerical weaponry such as Newton-Krylov-Poincare ́ solvers are required. These techniques allow for the computation of unstable steady flows, as well as travelling waves, or modulated travelling pulses. In this talk we will describe different strategies and techniques used to identify these hidden or unstable Navier-Stokes flows (from steady profiles, to travelling waves or relative periodic orbits) responsible for the transition. We will also explain how to track their linear stability when the parameters of the problem are varied so that bifurcations can be anticipated. Whereas these techniques have been essentially developed within the framework of fluid dynamics, they can easily be adapted to explore the phase space of other deterministic nonlinear PDE arising in physics.

[1] Deguchi, K., Meseguer, A. and Mellibovsky, F., Phys. Rev. Lett. , 112, 184502 (2014).

[2] Mellibovsky, F., Meseguer, A., Schneider, T. M. and Eckhardt, B., Phys. Rev. Lett. ,103, 054502 (2009).

[3] Meseguer, A.,Mellibovsky, F., Avila, M. and Marques, F. Phys. Rev. E, 80, 046315 (2009).

Biography

A. Meseguer is Associate Professor from the Department of Physics of the Universitat Politecnica de Catalunya (UPC). He graduated in Theoretical Physics from the University of Barcelona in 1992 and obtained his PhD in Applied Physics from the UPC in 1998. Between 1999 and 2002 he was an EPSRC Postdoctoral Research Officer and Lecturer in Physics at Oxford University. He came back from the United Kingdom to the Department of Physics at UPC and in 2003 was granted within the Ramon y Cajal postdoctoral scheme. A. Meseguer’s research focuses on hydrodynamic instabilities, bifurcations, dynamical systems and spectral methods for the accurate DNS computation of Navier-Stokes flows. His teaching activity is developed within the Engineering Physics degree at UPC, where he lectures numerical analysis, fluid dynamics and mathematical physics.

• Indexed published papers: 32

• h-index: 14

• Supervised PhD Theses: 3 (M. Avila, F. Mellibovsky and C. Panades)

• Theses currently under supervision: 2 (Roger Ayats and Baoying Wang)

29/11/2018, Aula 0.24 , E.I.I.

11:00-12:00

Rafael Castrejón-Pita

Senior Lecturer in Applied Science in Queen Mary, University of London (UK). 

“Formation, Breakup and Coalescence of Droplets”

From rain drops landing on the ocean to inkjet printing, drop formation and impact are ubiquitous processes in both nature and industry. It is generally accepted that there is still much to understand about drop breakup and splashing and these topics have gained additional importance motivated by the enormous potential of inkjet, spray and coating technologies in 3D printing. In fact, most methods aiming to model and predict droplet behaviour are either inaccurate or unsuitable for industrial applications. Furthermore, theoretical models are extremely hard to validate, and therefore as a consequence industry relies on empirical trial and error testing when developing and optimizing droplet technologies. In this talk I will give an overview of my studies that are aiming to bridge the existing gaps between applied and theoretical sciences, and also to an extent, those existing between academic and industrial work in the area of droplet science. The talk will focus on comparisons between experimental data and models and will highlight some interesting phenomena that have been shown recently to be arising in these topics. The first part of the talk will concentrate on the study of the breakup of liquid filaments and drop formation. My results will show that whether a thin filament has a tendency to break up or not into droplets will be dependent only on the liquid properties and the geometry of the system, and that this behaviour is universal. The second part of the talk will focus on the impact, coalescence, mixing and splashing of droplets. While the impact of droplets on to sessile solid substrates has been successfully studied in recent years, the impact on moving liquids has remained vastly unexplored due to practical difficulties. My talk will present the experimental arrangements that will overcome such limitations and will also investigate the impact of droplets on to diverse substrates including moving pools of the same liquid. My results will report the existence of distinct regimes of behaviour that are determined only by the initial dynamic conditions and the properties of the fluid. The third, and last part of my presentation, will conclude with some suggested directions for future work.

Biography

Dr. J.R. Castrejon-Pita is the Senior Lecturer in Applied Science in Queen Mary, University of London and a former Fellow of the University of Cambridge. He was awarded his MSc in Fluid Mechanics from the National University of Mexico in 2003, and his PhD in Quantum Optics from the Imperial College in 2007. He joined the Engineering Department at the University of Cambridge as a Research Assistant in 2006, and held the following positions within Cambridge University: Research Associate (2007 to 2014, tenured in 2012), Senior Member of Wolfson College (2008 to 2013) and Senior Research Associate (2014-present). Additionally, he became the Isaac Newton Trust Fellow and a Governing Body Fellow of Wolfson College in 2013. He carried out undergraduate teaching within the University of Cambridge as a Senior Demonstrator in the Cavendish Laboratory from 2007 to 2015, and as a Teaching Fellow in Mathematics in the Engineering Department from 2013 to 2015. He started his Lectureship in Queen Mary at the end of 2015. His interests lie in the field of fluid mechanics, particularly in the understanding of fundamental processes during liquid breakup, coalescence and splashing. His projects have been funded both by research councils (EPSRC-UK) and industry. His industrial partners include Airbus, FujiFilm, Xaar plc and Inca. He has published a total of 47 papers in peer-reviewed journals, including several in Physical Review. His collaborative network is extensive and includes Professors O. Basaran (Purdue University, US), Alfonso Ganan-Calvo (Seville University, Spain), J. Hinch and J. Lister (Cambridge University).

29/10/2018, Salón de Grados B, E.I.I.

12:00-13:00

Stefano Discetti. 

Profesor Titular de Universidad. Universidad Carlos III (Madrid). 

“Adverse-Pressure-Gradient effects on Turbulent Boundary Layers”

Wall-bounded turbulence is present in many relevant fluid-flow problems such as the flow around wings, land and sea vehicles, or in turbines, compressors, etc. Simplified scenarios, such as the zero-pressure-gradient (ZPG) turbulent boundary layers (TBL) developing over a flat plate, have been deeply investigated in the past. Unfortunately, TBL seldom develop under ZPG conditions, with pressure gradients having significant impact on their features. In particular, adverse pressure gradients (APG) might produce flow separation with the consequent losses in performances. In this talk a unique experimental database of APG TBL covering a wide range of Reynolds numbers and with different pressure-gradient histories is presented. The measurements were performed by means of hot-wire anemometry (HWA) and oil-film interferometry (OFI) in the Reynolds-number range , and for pressure-gradient intensities resulting in values of the Clauser pressure-gradient parameter in the range . The primary objective is to study and compare near-equilibrium and non-equilibrium APG TBLs developing on a flat plate, discerning Reynolds-number effects from those due to the pressure-gradient.

Biography

Stefano Discetti received his BSc (2007), MSc (2009), and PhD (2013) in aerospace engineering from the University of Naples Federico II. His PhD thesis focused on the development of tomographic PIV and its application to turbulent flows. As a part of his PhD studies, in 2010 and 2012 he worked in the Laboratory for Energetic Flow and Turbulence at Arizona State University on the development of 3D particle image velocimetry for the investigation of the turbulence generated by fractal grids. After receiving his PhD, he joined the Department of Bioengineering and Aerospace Engineering at Universidad Carlos III de Madrid where he currently holds the position of Profesor Titular de Universidad. His current research interests include the development of non-intrusive measurement techniques, wall-bounded turbulent flows and application of data-mining techniques to thermo-fluid-dynamic problems.