Numerical Investigations on Oscillating Aspiration Control in High-Load Compressor Cascades

Abstract

This current study presents a detailed analysis regarding three-dimensional separation flows controlled by steady and oscillating boundary-layer aspirations installed on suction surfaces of highly loaded planar compressor cascades. The influences of the oscillation parameters on the control effects are parametrically investigated with the objective of providing guidelines to determine the control parameters. The susceptibility to varying the aspiration locations as well as the control expenses of the steady boundary-layer suction methods are significantly improved due to the introduction of periodic oscillations into the aspirating flows. The effective excitation frequency spans a relatively wide bandwidth (from to ) only if the amplitude exceeds a threshold value (). Through a detailed comparative analysis on the steady and oscillating aspiration cases, the most prominent spatial change led by the oscillating aspiration is manifested by fully discretized separation vortices. These newly formed spanwise vortex tubes enhance the momentum exchange between the main flow and the recirculation zone, and hence alleviate the corner separation. Despite the increased local loss production caused by the increased vortical strength, the overall cascade performances are improved from a temporal average perspective. With the aid of the proper orthogonal decomposition method, the formation process of the discretized separation vortices is explored. It is found that the periodic disturbances originating from the suction slot are amplified, subject to the adverse pressure gradient and rollup, to form a series of vortical structures in the separated layers.