Wall permeability influence on turbulent structures and stress in compressible channel flows

Le résumé fourni par la source

Porous media are capable of promoting aerodynamic performance or suppressing noise radiation when applied to acoustic liners or airfoil trailing edges; however, the quantitative representations of the correlations between turbulence structures and wall permeability still remain an open question. In this study, direct numerical simulations of the channel flow over porous walls were conducted at a bulk Mach number of Mab=0.5 and a Reynolds number of Reb=4952. The permeable flow was modeled using the time-domain impedance boundary condition in the wall-normal direction. The results indicate that at a lower resistance, the resonance structures characterized by spanwise rollers would be induced with nearly fixed streamwise wavelengths, and the pre-multiplied spectrum of wall-normal velocity is mainly distributed throughout the viscous sublayer and buffer layer. The Helmholtz decomposition of velocities further reveals intensified dilatational motions in the near-wall region. To elucidate the relationship between the wall permeability and turbulent structures, we propose a novel decomposition method for the wall penetrability coefficient, applicable to porous wall flows. This decomposition method reveals that the flow penetrability at the wall is mainly enhanced by turbulent kinetic energy production and suppressed by the normal pressure gradient of the flow. As resistance decreases, turbulent kinetic energy production becomes the primary contributing factor. The decomposition method is then extended to the frequency domain to provide a more comprehensive understanding of the effect of wall permeability.

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