Two-dimensional instability of flow in a rough channel

Abstract

Linear stability of a two-dimensional flow in a channel with distributed surface roughness is considered. The structure of the disturbance field is related to the structure of the roughness when the ratio of the respective wave numbers is rational; they are not related if this ratio is irrational. It is shown that the stability problem is not unique in the former case but unique in the latter. It is found that disturbances in the form of traveling waves are destabilized by the presence of the roughness. A very good approximation of the critical Reynolds numbers can be found using only the dominant Fourier mode to represent roughness geometry.