Modelling Unsteady Transition Effects in an Axial Compressor

Wake induced transition is simulated at mid-span on a C4 stator blade in a 1.5 stage low speed axial compressor using the CFX γ – θ transition model. IGV and rotor wake inputs were created from a succession of Fourier series produced from experimental data. The purpose of the study was to understand the effectiveness of the γ – θ model implemented in a commercial code to predict the unsteady effects of wake induced transition. The γ – θ transition model was found to predict wake-induced transition and the subsequent calmed region caused by the passing wakes. The wake velocity defect creates conditions within the boundary layer such that the high disturbance energy, which is diffused into the boundary layer at the leading edge from the wake, initiates the transition process. This high disturbance energy travels through the boundary layer directly behind the wake.