| Time: | May 28, 2025, 4:00 p.m. (CEST) |
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| Meeting mode: | in presence |
| Venue: | V 9.41 Pfaffenwaldring 9 |
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Two topics are discussed. One is simulation of turbulent flow in porous media and the other is turbulent vortex breaking resulting from its impingement of an interface between fluid and porous domains.
LES is used to investigate a symmetry-breaking phenomenon in turbulent flow through periodic porous media composed of cylindrical obstacles. The phenomenon, driven by flow instabilities such as vortex shedding and bifurcations, causes the macroscale flow direction to deviate from the applied pressure gradient, especially within certain porosity and Reynolds number ranges. Large Eddy and Direct Numerical Simulations reveal that this effect leads to anisotropic turbulence and enhanced surface transport properties, with its occurrence highly dependent on obstacle geometry, porosity, and flow regime.
Although macroscale turbulent structures cannot form within porous media, in composite porous/fluid domains, they can be introduced by external turbulent flow impinging on the porous/fluid interface. Understanding how these macroscale turbulent structures interact with the porous/fluid interface is crucial for accurately modeling heat exchangers, canopy flows (relevant to forest fire modeling), and aerodynamic applications. This study provides novel insights into the behavior of macroscale turbulent vortices generated outside a porous medium as they impinge on and dissipate at the porous/fluid interface. Using large eddy simulation (LES), we modeled turbulent flow around a single macroscale solid obstacle, leading to turbulence impinging on a porous layer composed of microscale solid obstacles arranged in a 3D in-line configuration. By varying porosity and Reynolds number, we identified distinct turbulent flow regimes based on the interaction of turbulent structures with the porous medium. The LES-predicted turbulence kinetic energy budget—from production to dissipation—was analyzed to understand these interactions. Our findings reveal that at low porosity, macroscale turbulent structures diminish in scale as they penetrate the porous medium, whereas at very high porosities (greater than 0.95), these structures can persist within the medium. Additionally, we observed that while low porosities inhibit macroscale turbulence, they enhance convective heat transfer compared to the high-porosity case, underscoring the complex trade-offs between turbulence dynamics and heat transfer efficiency in porous systems.
Authors: Vishal Srikanth, Franco Zamora, and Andrey V. Kuznetsov
