MICROBURST FRONT DETECTION WITH FINITE TIME LYAPUNOV EXPONENTS
Keywords:Microburst. Vortex. Finite time Lyapunov exponents. Lagrangian coherent structures.
AbstractA microburst is a phenomena that occurs in the atmosphere which consist on a very intense downdraft that, after impinging on the ground surface, leads to strongly divergent winds at and just above the ground level. Such winds can reach more than 30 m/s-1 and are associated with high shear forces, representing a serious threat to aircrafts and buildings. The detection and tracking of the front of the microburst expansion at the ground level becomes an important and interesting field for researchers. Previous works show the detection of the vortex core but not for the vortex front. From velocity fields obtained from a LES simulation, we utilize Finite Time Lyapunov Exponents (FTLE) which measures the exponential divergence between particle trajectories. Then we identify manifolds which acts as separatrices of the flow and represent the edge or front of the vortex. By tracking the vortex front we also measure its displacement through time. Find the front of the vortex using only vorticity and velocity fields is complicated and imprecise. Therefore, the combination of these two methods represents a new approach in this particular problem.
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