Large Eddy Simulation of Pulsed Blowing in a Supersonic Compressor Cascade

Abstract

Large Eddy Simulation (LES) of a two dimensional supersonic compressor cascade is performed in the current study. It is found that the Shock Wave Boundary Layer Interaction causes a large scale of total pressure losses and presents strong fluctuation features. Thus the pulsed and steady excitation jets are applied to suppress the flow separations and to reduce the total pressure losses. Several impacting parameters, such as jet axial location, jet hole width, jet angle to the local blade surface and jet mass flowrate are chosen based on the primary analysis by the calculations by the Reynolds Averaged Navier-Stokes equations. In addition, based on the results of frequency spectrum and POD analysis, the excitation jet frequency is chosen for the pulsed excitation jet scheme. It is concluded that the pulsed excitation jet scheme achieves a 9.8% reduction of total pressure loss in comparison to the steady excitation jet scheme under the same time-averaged excitation jet mass flow rate. The excitation jets affect both the flow field near the jet hole on the suction surface and the flow field on the pressure surface via the management of the reflection shock wave. In addition, the excitation frequency dominates not only the time-averaged flow field, but also the second and third modes which stand for the unsteady structures in the flow field under the POD analysis. The first mode contains most energy in the flow field and the energy percentage decreases dramatically with the increase of the mode number. In comparison to the steady excitation jet scheme, the pulsed excitation jet scheme gathers more energy to the low orders of the modes, especially the first four modes. With the mixing effect and high dissipation rate of the high-frequency signals, the high-frequency signals shrink in the wake and the flow field builds up more uniformity.