Structural analysis on a hemisphere-cylinder at moderate Reynolds number and high angle of attack

摘要

Three-dimensional DNS has been performed on a hemisphere-cylinder at Reynolds number Re= 1000 and angle of attack AoA= 20° in order to analyze flow structures and wake frequencies. PIV experiments have also been carried out over the same geometry and flow conditions to validate the numerical results. Critical point theory has been applied in order to determine the topology patterns over the surface of the body. Critical points and separation lines on the body surface show the presence of three different flow patterns: separation bubble, "horn vortices" and "leeward vortices". Both, "horn vortices" and "leeward vortices" are found to be asymmetric and unsteady. The frequency related to "leeward vortices" oscillations has been identified both experimentally and numerically. Two more dominant frequencies, related to two different wake shedding modes have been found. On the other hand, POD has been performed and the four most energetic POD modes is found to be composed of a mixture of these three frequencies. They are modes on the wake shedding. Finally, DMD modes associated with these three frequencies are found on the symmetry plane close to the nose area. These modes represent different shear layer instabilities. Flow separation was found to be intrinsically linked with the observed shear-layer instability.