Wave-induced boundary layer flows over a flat and rippled bed

Abstract

The wave-induced boundary layer flow over a rippled bed is studied. A two-dimensional model aiming to solve the flow in the vicinity of the bed hasbeen developed. First the model is tested for a flat bed case and comparison is made with experimental data obtained by laser Doppler velocimetry(LDV) in two wave flumes presenting different characteristics. As the numerical and experimental results are compared, particular attention is given tothe mean Eulerian velocity profiles calculated from the two sources and the theoretical solution from Longuet-Higgins [Philos. Trans. Roy. Soc. Lond.A 245 (1953) 535]. Discrepancies are explained and the use of the available theory is discussed. The numerical model is then adapted to a rippledbed case and compared to experimental data obtained by LDV in a wave flume fitted with a rippled bed. The dynamical consistency of the model istested and the appearance of a vortex created at each half-wave cycle is shown. Mean velocity profiles are plotted at different locations along the rippleprofile. Different types of profile are obtained depending on the location. Mean velocity profiles from the model are studied for other flow and rippleconditions and it is shown that the profiles located at mid-distance between the crest and the trough always featured negative overshoot amplitudewhile the profiles located above the crest and the trough could be of either sign. An example of flow visualizations is also shown and qualitativecomparisons are made with the numerical model run for a similar case.