A General Theory of Flow-Instability Inception in Turbomachinery

A general eigenvalue theory on flow stability in turbomachinery is proposed with the emphasis on flow-instability onset. Based on this theory, a stall-inception model including the effects of complex solid geometry is developed for a multistage fan/compressors system. The capacity of the present model to predict the stall-inception point is assessed against experimental data of both a low-speed and transonic single rotor. Comparisons with a simplified two-dimensional model are performed to identify the nonnegligible effects of spanwise distribution of flowfield in a general configuration on the unstable mode of the concerned fan/compressors. It is verified that this model is capable of predicting mass flow at the stall-onset point of both subsonic and transonic flow with a reasonable accuracy, and it is sustainable in terms of computation cost for industrial application.