A Unified Framework for Characterization of Mode and Spike Routes to Rotating Stall

Abstract

In this thesis, we characterize modal and spike-type rotating stall inception for an isolated rotor using a low order, non-linear actuator disk model. The actuator disk representation is capable of capturing stall inception behavior given an axisymmetric total-to-static pressure rise characteristic. A parametric study of the effect of the derivative of the total-to-static pressure rise with respect to flow coefficient has been carried out to (i) define the links between the computed behavior of circumferentially propagating flow disturbances and those of established linearized analyses and (ii) describe both modes and spikes as different regimes of the same dynamical framework.

The results of the parametric study show three distinct regimes for the non-dimensional compressor characteristics examined. For total-to-static pressure rise characteristic slopes below 0.2, exponentially growing sinusoidal disturbances lead to the onset of rotating stall with growth time scales on the order of ten rotor revolutions. This behavior is characteristic of what is known as modal inception, or modes. For pressure rise slopes above 0.4, disturbances with no sinusoidal structures and with magnitudes of order of the mean axial flow were observed before the onset of rotating stall. The growth time scales of these disturbances were on the order of a rotor revolution. This behavior is characteristic of spikes. For pressure rise slopes between 0.2 and 0.4, both behaviors were observed. These results suggest a continuous transition between modal and spike inception, contrary to the description as two distinct phenomena.