Numerical Simulation of Low Frequency Oscillation in an Aeroacoustic Wind Tunnel

The low frequency pressure oscillation in an aeroacoustic wind-tunnel seriously affects the flow quality and acoustic measurement. At present, there are many measures to suppress pressure oscillation, but due to the lack of in-depth understanding of its generation mechanism, these methods are not of general significance. In this paper, based on the open-source software OpenFOAM, the SA-DDES method is used for the unsteady computations for the two-dimensional simplified wind-tunnel model. The steady and unsteady fields inside and outside the jet flow are showed. The computational results show that the nonlinear interaction between the large scale vortices rolled up by the instabilities of the shear layer and the front wall of the collector of the wind-tunnel is the main reason responsible for the low frequency oscillation in an aeroacoustic wind-tunnel. In addition, it is concluded that in the feedback loop path of the excitation-feedback effect, the pressure waves produced by the large scale vortex structures inside the shear layer impinging on the front wall of the collector are reflected by the rear wall of the plenum chamber. The end of the path that the pressure waves travel upstream is where vortex shedding happens, not the nozzle exit.