Experimental and theoretical study of wave–current turbulent boundary layers

Abstract

AbstractAn experimental study of turbulent wave–current boundary layer flows is performed using a state-of-the-art oscillating water tunnel (OWT) for flow generation and a particle image velocimetry system for velocity measurements. The current velocity profiles in the presence of sinusoidal waves indicate a two-log-profile structure suggested by the widely-used Grant–Madsen model. However, for weak currents in the presence of nonlinear waves, the two-log-profile structure is contaminated or even totally obliterated by the boundary layer streaming which is produced by the asymmetry of turbulence in successive half-periods of nonlinear waves. To interpret experimental results, a semi-analytical model which adopts a rigorous way to account for a time-varying turbulent eddy viscosity is developed. The model can accurately predict turbulence asymmetry streaming, which leads to successful predictions of the mean velocity embedded in nonlinear-wave tests and the current velocity profiles in the presence of either sinusoidal or nonlinear waves. Since the Longuet-Higgins-type streaming due to wave propagation is absent in OWT flows and not included in the semi-analytical model, future work is necessary to extend this study for applications in the coastal environment.