Proper orthogonal decomposition analysis and modelling of the wake deviation behind a squareback Ahmed body
Résumé
We investigate numerically the three-dimensional (3D) flow around a squarebackAhmed body at Reynolds number Re=104. Proper orthogonal decomposition (POD)is applied to a symmetry-augmented database in order to describe and model the flowdynamics. Comparison with experiments at a higher Reynolds number in a plane sectionof the near wake at midheight shows that the simulation captures several features of theexperimental flow, in particular the antisymmetric quasisteady deviation mode. 3D PODanalysis allows us to classify the different physical processes in terms of mode contributionto the kinetic energy over the entire domain. It is found that the dominant fluctuatingmode on the entire domain corresponds to the 3D quasisteady wake deviation, and thatits amplitude is well estimated from 2D near-wake data. The next most energetic flowfluctuations consist of vortex shedding and bubble pumping mechanisms. It is found thatthe amplitude of the deviation is negatively correlated with the intensity of the vortexshedding in the spanwise direction and the suction drag coefficient. Finally, we find thatdespite the slow convergence of the decomposition, a POD-based low-dimensional modelreproduces the dynamics of the wake deviation observed experimentally, as well as themain characteristics of the global modes identified in the simulation.