LINEAR TO NONLINEAR TRANSITION DURING THE SPIKE STALL PROCESS IN A LOW SPEED AXIAL FLOW COMPRESSOR ROTOR

A linear to nonlinear transition during the spike stall process of an axial flow compressor rotor is presented. Recently, some researchers thought that spike stall inception is directly induced by the tip leakage flow. However, the authors utilized unsteady full annular simulations and found that a second-order disturbance appeared two revolutions before the breakdown of the tip leakage flow in an axial rotor, associate with spike stall inception while the tip leakage flow is still stable. This second-order disturbance grew rapidly in the next two revolutions and the process was unlike the low order disturbance development in modal stall inception. The response of the compression system was still linear in this process. The rapidly developing second-order disturbance made the tip leakage flow unstable, leading to the start of spike stall inception. The response of the compression system became nonlinear in this process.