A Unified Framework for Compressor Stall Inception

Abstract This article presents a first-of-a-kind description of compressor rotating stall inception that unifies the two different routes to stall reported in the literature over the past four decades. A low-order dynamic system model, an actuator disk analysis, is shown to capture these two transient, stall inception behaviors, namely, modes: the growth of small amplitude, long length scale (on order of compressor circumference), sinusoidal velocity perturbations, versus spikes: short length scale (on order of blade pitch) velocity disturbances with fast, nonlinear growth. The analysis demonstrates that the two distinctly different processes are on a continuum of compressor dynamic behavior and can be captured by the same unifying framework. Their features, including the different length and time scales, are revealed without explicit modeling of the blades. The differentiator for stall inception behaviour is shown to be the slope of the compressor total-to-static pressure rise characteristic at flows below that corresponding to the peak pressure rise, i.e., to the left of the peak. Small positive slopes to the left of the peak lead to the growth of modes into fully developed rotating stall cells. Large positive slopes lead to a more rapid evolution of spikes into stall cells. The actuator disk simulations indicate that these two types of transient fluid motions bound a range of stall inception behaviors that depend on the compressor pressure rise characteristic slope. The article quantifies the slopes that set the stall inception behavior. Data from compressor experiments and full annulus unsteady Reynolds-averaged Navier–Stokes simulations are used to connect the shapes of radially varying compressor characteristics, in the rotating stall regime, to flow features including blade leading-edge and corner separations. The experiments and full annulus computations confirm that the low-order model successfully captures the transient flows and physical mechanisms of rotating stall inception.