An empirical model for velocity in rough turbulent oscillatory boundary layers

A novel empirical model for the streamwise velocity in oscillatory boundary layer flow, valid in the rough turbulent regime, is presented. The model consists of simple expressions that require only the free-stream velocity time-series and equivalent sand-grain roughness length of the bed to be known a priori. A frequency-independent attenuation and phase lead is assumed for all flow harmonics, expressions for which are extracted from data from previous experimental studies made in 3 different oscillatory flow tunnels. Only the oscillating component of the flow is considered in the model; steady streaming is neglected. Errors in kinematics predicted by the model are typically two orders of magnitude smaller than the maximum oscillatory velocity in the free-stream. Hence, it is well-suited to engineering application due to its simplicity and accuracy