Experimental investigation of wave boundary layer

A review is presented of experimental investigation of wave boundary layer. The review is organized in six main sections. The first section describes the wave boundary layer in a real-life environment and its simulation in the laboratory in an oscillating water tunnel and in a water tank with an oscillating seabed. A brief account is given of measured quantities, measurement techniques (LDA, PIV, flow visualization) and limitations/constraints in the experimental investigation of the wave boundary layer in the laboratory. The second section concentrates on uniform oscillating boundary layers with a smooth bed. The boundary layer process is described over the entire range of the Reynolds number (Re from practically nil to Re = O(107)), from the laminar regime to the transitional regime and to the fully developed turbulent regime. The third section focuses on the effect of the boundary roughness. Results of recent research on wave boundary layers over a bed with large roughness (such as a/ks = O(1)) are also included in the review. The fourth section describes the effect of superimposed current on the wave boundary layer. The entire ¿spectrum¿, namely from the wave-dominated regime to the current-dominated regime, is covered. Processes such as turbulence reduction/re-laminarization, and increase/decrease in the bed shear stress are presented. The fifth section considers various effects on the wave boundary layer such as the non-uniformity (that due to change in the boundary roughness and that due to change in the flow geometry, i.e., the divergent/convergent environment); irregular waves, the angle of attack of waves; the effect of an externally generated field of turbulence; the suction and injection at the boundary (the ventilated boundary layers); and the vegetation. Also a brief account is given of the steady streaming (in a progressive wave and in a standing wave). The final section summarizes the results of recent research on coherent structures in wave boundary layers.