RECTIFIED FLOW OVER AN ELONGATED TOPOGRAPHIC FEATURE ALONG A VERTICALWALL

Alongshore oscillatory flows over an elongated topographic feature nex t to a vertical wall for a homogeneous, rotating fluid were investigat ed by means of numerical and laboratory experiments. The physical expe riments were conducted in the Grenoble 13-m diameter rotating tank, in which an elongated obstacle of limited longitudinal extent was placed along the vertical sidewall. The background oscillating motion was ob tained by periodically varying the platform angular velocity. Fluid mo tions were visualized and quantified by direct velocity measurements a nd particle tracking. The numerical model employed was a tridimensiona l model developed by Haidvogel et al. It consists of the traditional p rimitive equations, that is, the Navier-Stokes equations for a rotatin g fluid with the addition of the hydrostatic, Boussinesq, and incompre ssibility approximations. (The experiments described here employ the h omogeneous version.) The numerical formulation uses finite differences in the horizontal and spectral representation in the vertical dimensi ons. Both the laboratory and numerical experiments show that in the ra nge of dimensionless parameters considered, two distinct flow regimes, based on general properties of the rectified how patterns observed, c an be defined. It is further shown that the flow regime designation de pends principally on the magnitude of the temporal Rossby number, Ro(t ) defined as the ratio of the flow oscillation to the background rotat ion frequency. Good qualitative and quantitative agreement is found be tween the laboratory experiments and the numerical model for such obse rvables as the spatial distribution of rectified Bow patterns. Several other flow observables are defined and their relation with the system parameters delineated.