Direct effects of boundary permeability on turbulent flows: observations from an experimental study using zero-mean-shear turbulence

McCorquodale, Mark W.; Munro, R. J.

Abstract

The interaction of zero-mean-shear turbulence (generated using an oscillating grid) with solid and permeable boundaries is studied experimentally. The influence of wall permeability is characterised using the permeability Reynolds number, ReK, which represents the ratio of the typical pore size in the permeable medium to a viscous length scale. Instantaneous velocity measurements, obtained using two-dimensional particle imaging velocimetry, are used to study the effect boundary permeability has on the root mean square of fluctuating velocity components, the vertical flux of turbulent kinetic energy (TKE) and conditional turbulent statistics associated with events in which intercomponent energy transfer is concentrated. When ReK≲0.2 the boundary acts as if it were impermeable; results indicate the interaction is dominated by the kinematic blocking effect of the boundary on the boundary-normal TKE flux, with additional mechanisms acting through intercomponent energy transfer. The results show these mechanisms are inhibited as ReK increases, due to the transportation of turbulent energy into the porous medium as the macroscopic blocking condition is relaxed, thereby reducing TKE within the boundary-affected region and inhibiting the formation of high-pressure stagnation events that are responsible for intercomponent energy transfer. The results illustrate how the turbulence structure above a permeable boundary is sensitive to the blocking effect on the boundary-normal turbulent velocity. In light of these results, we propose that further analysis is required to establish the validity of a commonly used model of the boundary conditions enforced at the boundary of porous media, in which a no-penetration boundary condition on the boundary-normal velocity component is proposed.

Citation

McCorquodale, M. W., & Munro, R. J. (2021). Direct effects of boundary permeability on turbulent flows: observations from an experimental study using zero-mean-shear turbulence. Journal of Fluid Mechanics, 915, Article A134. https://doi.org/10.1017/jfm.2021.160

• Journal Article Type: Article
• Acceptance Date: Feb 17, 2021
• Online Publication Date: Mar 31, 2021
• Publication Date: May 25, 2021
• Deposit Date: Apr 16, 2021
• Publicly Available Date: Oct 1, 2021
• Journal: Journal of Fluid Mechanics
• Print ISSN: 0022-1120
• Electronic ISSN: 1469-7645
• Publisher: Cambridge University Press
• Peer Reviewed: Peer Reviewed
• Volume: 915
• Article Number: A134
• DOI: https://doi.org/10.1017/jfm.2021.160
• Keywords: turbulent boundary layers, homogeneous turbulence, boundary layer structure
• Public URL: https://nottingham-repository.worktribe.com/output/5433640
• Publisher URL: https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/abs/direct-effects-of-boundary-permeability-on-turbulent-flows-observations-from-an-experimental-study-using-zeromeanshear-turbulence/38B535D59C6DE9FFFE10C1B8459D6068
• Additional Information: Copyright: © The Author(s), 2021. Published by Cambridge University Press