Laboratory Studies of Low Vortices in a Low Froude Number FlowPasting over an Isolated Obstacle

Abstract

The present paper mainly focuses on the generation and developmentof lee vortices for the low Froude number density stratified flowpassing over an isolated obstacle. A series of laboratory experimentswere carried out by towing-tank equipments to simulate the airflowpassing over a large terrain. Based on the similarity principle, theFroude number of the stratified flow, the stratified condition, and therotation parameter are chosen in the specified scope. Our studies showthat the lee vortices can appear in the non-rotational and rotationalcases. For the non-rotational fluid, the lee vortices generate onlyunder the condition of strong stratification and the small Froudenumber (0.1<Fr<0.3). However, the lee vortices can be formed underthe condition of relatively strong stratification and the properFroude number (0.1<Fr<0.5) for the rotational fluid. Theresults of the divided experiments including non-rotational androtational cases show that the formation mechanism of lee vortices isdifferent for non-rotational flow and rotational flow. The leevortices are created by the tilting term of perturbation velocity forthe non-rotational flow, but for the rotational flow, the β-effectassociated with the horizontal convergence and divergence of thehorizontal perturbation velocity is more important.