Sponsors: Office of Naval Research (ONR), Carlsberg Breweries
Collaborators: Prof. Steve Ceccio, Prof. Christian Poelma (TU Delft)
Sheet and Cloud Cavitation
A significant source of performance deterioration and erosion in Naval vessels, this is a challenging multi-scale and multiphysics two-phase fluid flow problem. My Ph.D. research was on using radiation-based measurments to investigate this complex optically opaque flow field. One of the main findings from that study was the importance of mixture compressibility effects on cavity shedding dynamics. I continue to work on this topic and am currently working on two studies,
understanding the effect of cavitation dynamics on food processing (Carlsberg)
understanding the scaling of partial cavitation with geometric scale from an erosion perspective (ONR-HIFOIL)
Vortex cavitation
Unlike sheet and cloud cavitation, vortex cavitation is more localized and is usually the first type of cavitation observed. I have worked on understanding the processes of vortex cavitation on several geometries and continue to work on this topic. To study this problem, we have used optical velocimetry measurement techniques to characterize the complex turbulent single-phase flows
Cavitation of three-phase mixtures
Cavitation can occur during processing of food mixtures, which can contain all three phases. This can result in influencing the processes and is important to understand. I am currently working on an effort to use radiation-based measurements to understand the effect of cavitation on food processing.
Ventilated Supercavities
By injecting non-condensable gas, it is possible to establish long cavities that can have benefits such as reduced drag. Our recent work was on investigating the gas loss at ventilated cavity closures under several conditions using X-ray-based measurements. The study showed the importance of the wake characteristics on cavity stability. I am interested in continuing this work and am open to collaborations.
Sponsors: DARPA-Arcadia, ONR- Adaptive Multifunctional Surfaces, CNRE (Center for Naval Research and Education)
Collaborators: Prof. Jon Estrada (UMich), Dr. First, Dr. Lee, Dr. Riley, Dr. Molina (all NRL)
Most of us who have canoed or kayaked a river may have noticed the prevalence of algae growth on objects in prolonged contact with water. Such growth can happen on objects in the ocean, both on the surface and underwater. The presence of these can result in many undesirable effects, mainly an increase in hydrodynamic skin-friction drag, which can be substantial.
This problem is at the intersection of biology, fluid dynamics, materials science, chemistry, and many other fields. Predicting the growth and drag of biofouling is essential for improved design and identifying an optimum cleaning schedule, among other things. However, understanding and predicting the drag of live biofouling, a complex interplay between biology, fluid dynamics, and materials science, is challenging.
One of the main challenges is repeatable measurement of drag and roughness quantities at nominally similar conditions. This is due to the interaction of the flow with live fouling, changing its composition and distribution during drag measurment making repeatable measurments challenging. In addition, removal of specimens from the growth chamber to the drag measurement setup can introduce additional errors. The approach we have adopted is to study live fouling (at NRL, Key West) in all its complexities and identify important hydrodynamic information such as coverage, material compliance, etc., and use artificial surrogates to understand the near-wall flow in a laboratory setting using turbulent channel flows and drag balances.
Live Fouling Studies
Our biofouling team works with scientists at the Naval Research Laboratories at Key West, FL (NRL-KW) to study the growth, drag, biological composition, and roughness characteristics of live biofouling using an open-loop growth chamber (funded by ONR). The team comprises of hydrodynamics experts, marine biologists, and materials scientists. Some of the aims of the study is to understand
The effect of ambient conditions, mainly flow velocity and duration, on the growth,
biological composition quantified using DNA sequencing
fouling coverage and roughness/height distribution
drag using a bespoke turbulent channel flow setup using natural seawater
Live Fouling-Inspired Roughness Study
As mentioned earlier, studying drag production mechanisms of live fouling is challenging due to time-varying composition as well as sensitivity to conditions. To understand the mechanisms of how drag is generated (with an intent to improve prediction models), artificial roughness configurations (with and without compliance) are studied systematically based on findings from the live fouling study. This study is performed at the University of Michigan using a turbulent channel flow setup and a boundary layer setup equipped with a drag balance (current work).
Sponsors: None
Collaborators: None
Turbidity currents are gravity-driven flows characterized by a dense mixture of sediment and fluid moving into lighter ambient fluid due to density differences. These currents occur in various natural settings such as oceans, avalanches, and volcanic flows. They have been extensively studied in laboratory settings (Meiburg and Kneller 2010; Ikeda and Testik 2021; Xie et al. 2023; Gadal et al. 2023), focusing primarily on the velocity of the current front, particle deposition, and the entrainment of ambient fluid.
Despite many studies and recent experimental work, reliable time-resolved measurement of sand volume fraction to understand the flow processes has not been performed. In our endeavor to study this flow, we have applied and validated X-ray based measurment of particle-laden (sand) using high-speed photon-counting X-ray detectors. We aim to further advance understanding of such flow by performing densitometry to measure time-varying volume fraction fields of a spatially evolving turbidity current generated using a lock-exchange. By integrating these observations with existing knowledge, we seek to enhance our understanding of turbidity current dynamics in both Boussinesq and non-Boussinesq limits, contributing to broader insights into sediment transport processes in natural environments.
Sponsors: DARPA-DRAG
Collaborators: Prof. Anish Tuteja (UMich), Prof. Krishnan Mahesh (UMich), Prof. Matt Bross (PSU-ARL), Dr. Bill Straka (PSU-ARL), Prof. Gareth McKinley (MIT), Prof. Steve Ceccio
For marine vessels, skin friction is the dominant source of energy loss, responsible for more than 50% of total fuel consumption. Over the years, numerous active and passive techniques have been developed to overcome this issue. While some techniques have demonstrated drag reduction over flat surfaces, they often require energy input or become impractical for large-scale applications such as ship hulls due to high fabrication costs. In contrast, spray-on Super Hydrophobic Surface (SHS) has shown great effectiveness in terms of both effectiveness and cost efficiency. Previous studies Golovin et al. (2016) have demonstrated that randomized spray-on Super Hydrophobic Surfaces (SHS) achieve significant drag reduction (DR) at high Reynolds numbers (Re). SHSs trap a thin air layer near the surface structures, which induces slip velocity in the flow and thereby reduces drag. Drag reduction (DR) depends upon different surface and flow properties such as Reynolds number, RMS roughness, solid fraction, Wenzel roughness and so. Despite this knowledge, the role of surface roughness and the underlying chemical composition of the SHS under consideration on the observed DR performance is yet to be fully understood.
In this study, drag characteristics of several SHS fabricated with Fluorinated Silica NanoParticles (FSNP) and Fluorodecyl Polyhedral Oligomeric SilSesquioxane (FPOSS) are tested in a turbulent channel flow. The coating was applied onto a stainless-steel substrate at different pressures and composition to achieve distinct roughness profiles. Drag performance was quantify based on pressure drop measurements in a turbulent channel flow across a range from 10,000 to 55,000. Measured drag is compared with a hydrodynamically smooth surface to quantify DR.
Additionally, surface longevity was tested by exposing the surface under turbulent flow at constant for prolong period. In real-life applications, surfaces are often exposed to varying pressure conditions during operation. Therefore, it is important to examine how hydrodynamic pressure affects superhydrophobic surfaces. To address this, SHSs were also tested under both sub-atmospheric and elevated pressure conditions.
Sponsors: ONR, Naval Nuclear Laboratories (NNL)
Collaborators: Prof. Steve Ceccio (UMich), Prof. Jesse Capecelatro (UMich)
Augmenting Radiation-Based Measurments (3D X-ray Tomography)
Direct quantification of volume fraction fields is essential for understanding and modeling complex multiphase flows. Radiation-based methods, including densitometry (2-D) and tomography (3-D), enable direct fraction measurement irrespective of opacity without the need for intrusive probes. However, high-speed applications pose significant challenges, and the use of commercially available CT systems is not feasible. In this study, a high-speed, limited-angle Scanning Electron Beam X-ray Tomography (SEB-XT) system has been developed and tested at the University of Michigan (UM). The UM SEB-XT system has been demonstrated to be capable of measuring volume fraction fields at a rate of 600 images per second. System performance has been characterized using both static and dynamic testing targets as well as a bubble column.
Estimating Flow Quantities from Particle Tracks
Obtaining high-resolution pressure and velocity measurements from turbulent flows, both in time and space, is of great importance across engineering, biological, and environmental sciences. The objective of this project is to develop an open-source framework that combines optical particle tracking measurements from experiments with particle-based simulation techniques to obtain
accurate and fast representation of the flow state based on physical constraints, and
insight into the quality of the experimental measurement.
Unlike previous approaches, information from particle tracks obtained experimentally remains in a Lagrangian frame of reference, and techniques from smooth particle hydrodynamics (SPH) are leveraged to accurately reconstruct the local pressure field and other flow quantities of interest