InterPore2023

Interfacial interaction of a porous periodic topology adjacent to a turbulent fluid flow by highly resolved PIV measurements

22 May 2023, 14:45

15m

Oral Presentation (MS06-B) Interfacial phenomena across scales MS06-B

Speaker

Tobias Fuhrmann (University of Stuttgart)

Description

For a wide range of engineering applications such as transpiration cooling, filtration processes, heat exchangers and geothermal engineering, understanding how porous media with different topologies interact with turbulent free flows is crucial. For this purpose, the focus is on the efficient design, operation and optimisation of such engineering applications and relies on comprehensive understanding of the exchange of mass, momentum and energy across the interface between the porous medium and the free flow.

A controversial point of discussion is whether the transport at the interface is mainly diffusion or advection controlled. It is demonstrated that a viscous sublayer exists close to the permeable wall only when the intrinsic permeability of the porous medium is small compared to the viscous length scale of the fluid [1]. If this requirement is fullfilled, a direct proportionality between the strain rate at the interface and the velocity difference between the interfacial velocity and the Darcy velocity inside the porous domain can be derived as an empirical boundary condition for coupling the porous media region and the free flow at the interface [2]. With the increase of the permeability Reynolds number [3] turbulent fluctuations start to penetrate into the porous media region, which is known as turbulent pumping, while simultaneously the porous media topology also affects the turbulent flow in the free flow region [4]. Due to visual accessibility inside of the porous model and the possibility of achieving high porosity, a triply periodic minimal surface topology is used as porous medium. Thus investigating both the penetration of turbulent fluctuations and the dependence of the porous media topology on the turbulent free flow is possible.

In this talk results of highly resolved PIV measurements are presented for such a porous periodic topology adjacent to a turbulent fluid flow, for both inside the porous medium region and at the interfacial region. It will be discussed (a) how the periodicity of the triply periodic minimal surface model influences the interfacial layer of the free flow, (b) how the flow field behaves inside the periodic porous region and (c) which flow phenomena occur at the interface of the porous medium and the free flow, specifically emerging vortices.

References

[1] S. Hahn, J. Je, and H. Choi. Direct numerical simulation of turbulent channel flow with permeable walls. Journal of Fluid Mechanics, 450:259 – 285, 2002.

[2] G. S. Beavers and D. D. Joseph. Boundary conditions at a naturally permeable wall. Journal of Fluid Mechanics, 30(1):197–207, 1967.

[3] W. P. Breugem, B. J. Boersma, and R. E. Uittenbogaard. The influence of wall permeability on turbulent channel flow. Journal of Fluid Mechanics, 562:35–72, 2006.

[4] K. Suga, Y. Okazaki, and Y. Kuwata. Characteristics of turbulent square duct flows over porous media. Journal of Fluid Mechanics, 884, 2020.