NUMERICAL EXPERIMENTS OF VORTICES IN THE WAKES OF LARGE IDEALIZED MOUNTAINS

The Purdue Mesoscale Moder (PMM) is applied to study the flow past lar ge idealized mountains under a low Froude number. Results show that fo r Reynolds numbers in the range of 4 < Re < 1000, as long as the flow is symmetric to the central line of a symmetric mountain, two vortices remain stably attached to the mountain. For Re less than or equal to 100, the size of the attached vortices after 120 hours of integration increases linearly with the increase of Re, but the size decreases sli ghtly with Re for Re > 100. Results also show that small perturbations in the oncoming wind, the inclination of the oncoming wind and major axis of the mountain, the mountain shape, and the Coriolis force all c an contribute to atmospheric vortex shedding. The Reynolds number is n ot a good indicator of whether a vortex will stay or break away from t he mountain in the atmosphere. When the earth's rotation is included, the simulated pressure field and wind increase considerably on the lef t-hand side (facing downstream) of the mountain, which is quite differ ent from that of an irrotational flow, although the pattern of vortex shedding. is similar. It is also found that the Reynolds number and be ta effect can change the propagating speed but not the period of vorte x shedding. On the other hand, the shape and size of the mountain and asymmetry of the oncoming wind can strongly influence the character of vortex shedding.