Towards Understanding and Resolving Natural Shock Oscillation in Transonic Compressors

The mechanisms of shock oscillation in a transonic compressor with a laminar shock-boundary layer interaction are investigated with Large Eddy Simulation using the Rolls-Royce Hydra LES solver. The effect of shock position (bow, passage, swallowed shock) is investigated. It is found that the collapse and recovery of the laminar separation bubble (shock-induced separation) due to a Kelvin-Helmholtz instability is the root of the oscillation, and that this instability most likely occurs when the shock induced separation bubble is large enough (passage shock) and severe density and velocity gradients exist. Therefore, the oscillation does not occur for a bow shock or swallowed passage shock.