Laboratory experiments on mountain induced rotors
Knigge, Christoph ; Etling, Dieter ; Paci, Alexandre ; Eiff, Olivier
Stratified flow over obstacles has received considerable interest in the last decades in atmospheric, hydraulic or oceanographic contents. Much theoretical, numerical and experimental work has been performed for the case of mountain lee waves. It has been also known since a long time, that flow reversal can occur on the leeward slope of mountains under special environmental conditions. These flows are called rotors and are characterized as a very turbulent quasi two-dimensional vortices with horizontal axis parallel to the mountain. Despite their danger for airplanes in case of airports near mountain ranges, not much research on rotors has been performed in the last decades. This has changed quite recently with the large international field experiment T-REX (Terrain-induced Rotor Experiment, Grubisic et al., 2008), which has been performed in the Sierra Nevada range in early 2006. Rotors have also been observed at smaller mountains as on the Falkland Islands recently (Mobbs et al., 2005). Recent numerical simulations (Vosper, 2004, Hertenstein, and Kuettner, 2005) have revealed, under which environmental conditions (wind speed, stratification) rotors can form in the lee of mountain-ridges. For the classical case of mountain lee-waves also various laboratory experiments have been performed (see e.g. Baines, 1995; Eiff et al. 2005), using mostly stratified towing tanks. In contrast no systematic laboratory experiments on mountain rotors have been performed so far. The main motivation of this project was to fill this gap and perform laboratory experiments on mountain rotors, using the recent numerical simulations of Vosper (2004) as a guide. The project last for 30 working days during which about 150 experiments were done. These experiments allow to built a regime diagram for the observed flow phenomena (lee waves, rotors, hydraulic jumps) that can be compared to the results provided by the numerical simulations of Vosper (2004). An article (Knigge et al., 2009) has been submitted to Quart. J. Roy. Meteor. Soc.
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