Lattice Boltzmann direct numerical simulation of interface turbulence over porous and rough walls

To discuss the turbulent flow physics over porous walls, direct numerical simulation (DNS) of a porous-walled channel flow at the bulk Reynolds number of 3000 is performed by the D3Q27 multiple-relaxation time lattice Boltzmann method. The presently considered porous layer, whose porosity is 0.71, consists of interconnected staggered cube arrays. For understanding the influence of the wall permeability on turbulence, DNS of an impermeable rough walled channel flow is also conducted. By two-point autocorrelation, one-dimensional energy spectrum and proper orthogonal decomposition (POD) analyses, the existence and characteristics of the transverse pressure waves induced by the Kelvin-Helmholtz (K-H) instability over the porous and rough walls are elucidated. The structure, wave lengths and power spectra of the transverse waves are discussed in detail. The influence of the K-H instability on turbulence is also clarified.