11:10 - 11:25

11:25 - 11:40

Stanisław Gepner

Whispers of Order amidst the turbulent storm. Invariant States and Quiescent Interludes in turbulent square duct flow.

Warsaw University of Technology

Turbulence, a complex and seemingly chaotic phenomenon, often defies our understanding. However, within this chaotic realm, hidden patterns and underlying structures can emerge. This research delves into the intriguing relationship between invariant states and quiescent interludes in turbulent square-duct flow.

Invariant solutions govern turbulent dynamics by attracting the disturbed flow states along their stable manifolds only to eject them in one of the unstable directions. These hidden states constitute the turbulent skeleton and provide a glimpse into the hidden order present amidst the turbulent chaos. The quiescent interludes of turbulence, and moments of relative calm within the turbulent storm, offer unique opportunities to study these invariant states.

By analyzing the dynamics of square-duct flow, we uncover a captivating connection between invariant solutions and the occurrence of quiescent interludes. We demonstrate that these periods of calm are not random but rather reflect the influence of specific invariant solutions.

Understanding turbulence, one quiet moment at a time, our research sheds light on the hidden structures that shape turbulent behaviour and offers valuable insights into the dynamics of complex fluid flows.

11:25 - 11:40

11:40 - 11:55

Dawid Strzelczyk

Robust and memory-efficient simulations of inertial flows with meshless Lattice Boltzmann Method.

Institute of Theoretical Physics, University of Wrocław

One of the limitations of the Lattice Boltzmann Method in simulating inertial flows is the coupling of the discretization of space to the velocity discretization. It requires an increase of the size of computational lattices in order to increase the Reynolds number at a fixed velocity and viscosity. In this work, we adopt the recently proposed meshless formulation of Lattice Boltzmann Method to the problem of inertial flows. In contrast to the standard algorithm, it allows to decouple space and velocity discretizations. Thus, one can change the conversion factors from lattice to physical units for length, velocity, and body force by scaling the streaming distance. In turn, one increases the Reynolds number without increasing the size of the discretization. We measure the accuracy and efficiency of this approach in the K\'{a}rm\'{a}n vortex street behind a circular obstacle and the flow through a porous sample in Darcy and inertial regime. Additionally, we apply the meshless streaming step to the recently proposed fixed relaxation time tau=1 LBM to extend its applicability to model inertial flows.

11:40 - 11:55 (withdrawn)

Piotr Zdybel

Scaling law for a buckled elastica in a shear flow

Institute of Fundamental Technological Research, Polish Academy of Sciences

11:55 - 12:10

Maciej Matyka

Inertial effects on fluid flow in complex porous media

Institute of Theoretical Physics, University of Wrocław

Porous media are ubiquitous and play a crucial role in various fields, such as the extraction industry and medical applications. The transport of mass and energy through these complex and multiscale materials primarily occurs at the pore level, characterized by interconnected and tortuous structures. Tortuosity is often treated as the third pillar of porous media description, next to porosity and permeability. This parameter quantifies the elongation of transport paths in phenomena like fluid flow, diffusion, and electric current transport. When considering fluid dynamics within porous media, researchers typically assume a slow-creeping regime. However, there are situations where the flow is faster, introducing deviations from basic linear models and subsequently influencing tortuosity.

Here, we present our latest observations on tortuosity in a three-dimensional porous media model under relatively high Reynolds numbers (Re). We aimed to examine tortuosity during the transition from the Darcy to the non-Darcy (inertial) regime. Unexpectedly, we found that tortuosity does not follow a natural monotonous decrease with increasing flux. To shed light on this, we first provide an overview of the method and algorithm employed to compute tortuosity. We then attempt to understand the physical flow mechanisms causing this observed ambiguity. In analyzing our findings, we highlight the significance of inertial effects and the kinetic energy confinement within the vortices emerging in the flow.

Funded by National Science Centre, Poland under the OPUS call in the Weave programme 2021/43/I/ST3/00228.

12:10 - 12:25

Robert Straka

Bloody LBM: bypass grafts simulation tool

AGH - UST

The assessment of volumetric blood flow in bypass grafts stands as a pivotal parameter indicative of the overall success of surgical intervention. In cases where blood flux diminishes significantly, the efficacy of the bypass may be compromised, potentially leading to failure. We present a novel bypass graft simulation tool (currently under development :). This tool comprises three integral components: segmentation of X-ray coronary angiography, bypass graft planning, and simulation of blood flow, alongside an anastomosis optimization module. Our presentation deals primarily with the blood flow modeling aspect, which is performed by the Lattice Boltzmann Method. We conduct simulations on three scenarios involving the left coronary artery -- healthy, stenosed and stenosed with a bypass -- and verify our findings with those obtained from the SimVascular - a specialized software for medical image data segmentation and patient specific blood flow simulation and analysis.