Book Description

A research program to investigate fundamental mechanisms of rotating stall in axial-flow turbojet engine compressors is described. Analysis of the lift hysteresis of an oscillating elliptic airfoil at stall indicates that including the effects of a moving separation point on the criterion for separation of the boundary layer has a negligible effect on the computed lift hysteresis. Attempts were made to modify a previously developed rotating small-disturbance stability theory based on an actuator representation of blade rows so as to improve theoretical predictions of rotating stall. These attempts included modifications of blade-row representation, inclusion of viscous dissipation effects in the flow away from blade rows, and extension of the stability theory to include three-dimensional unsteady flows. The only modification of the stability theory which appeared to improve theoretical prediction of flow instability and for which numerical results were obtained was the assumption of actuators of finite thickness incorporated in the analysis of a configuration with a rotor plus a row of upstream guide vanes. It is concluded that more research is required before a final assessment of the validity of the rotating small-disturbance stability theory can be made. An annular cascade was designed and fabricated. The preliminary rotating-stall data obtained from the cascade are presented and discussed.