Scaling of turbulence structures in very-rough-wall channel flow

Abstract

The streamwise velocity statistics in fully-developed rough-wall channel flow have been investigated for the cases of two very different surface topologies with similar Reynolds numbers. The first surface consisted of a sparse and isotropic grit having a highly non-Gaussian distribution, while the second surface was covered with a uniform, anisotropic mesh comprised of twisted, rectangular elements. The flow was demonstrated to be fully-developed and two-dimensional up to the fourth moment of velocity. Though the flow over both surface types appear to exhibit a limited logarithmic region, the regions of inner and outer scaling over the mesh surface fail to overlap. The influence of the spanwise periodicity of the mesh upon the outer scaling is discussed.