Experimental studies of strongly stratified flow past three-dimensional orography

• DOI: 10.1017/s0022112099005133
• Publication Date: 2002-07-27T09:23:06Z
• Authors: S. B. VOSPER; I. P. CASTRO; W. H. SNYDER; S. D. MOBBS
• Keywords: Froude number; Strouhal number; Stratified flows; Vortex shedding; Orography; Wave drag

Stably stratified flows past three-dimensional orography have been investigated using a towing tank. Flows idealized axisymmetric in which the Froude number, F h = U / Nh (where is speed, N buoyancy frequency and height of obstacle) less than unity studied. The considered consists two sizes hemisphere cones different slope. For all obstacles measurements show that as decreases, drag coefficient increases, reaching between 2.8 5.4 times value neutral flow (depending on obstacle shape) for [les ]0.25. Local maxima minima also occur. These are due to finite depth tank can be explained by linear gravity-wave theory. Flow visualization reveals lee wave train downstream amplitude O ( ), smallest occurring steepest cone. Measurements obstacles, dividing-streamline height, z s , described reasonably well formula =1− . acoustic Doppler velocimeter wake vortex shedding occurs when ]0.4 period independent height. Based velocity both (plus additional smaller hemispheres), it shown blockage-corrected Strouhal S 2 c fL collapses onto single curve plotted against effective Here, free-stream speed based mass-flux considerations, f L width at /2. Collapse data obtained shapes cone made triangular rectangular plates. Indeed, values these similar this suggests despite fact widths vary with length scale determines vortex-street dynamics. Experiments conducted splitter plate indicate mechanism provides major contribution total (∼25%). addition an upstream pointing ‘verge region’ increase significantly strongly flow. Possible mechanisms discussed.