Axial flow rotor unsteady response to circumferential inflow distortions

The unsteady response of an axial flow fan rotor to steady, circumferential inflow velocity distortions has been evaluated by investigation of the unsteady normal force and pitching moment on a chordwise element of a rotor blade. Experimental measurements of these unsteady characteristics are presented as a function of the geometry of the rotor -- stagger angle, solidity and steady angle of incidence -- for sinusoidally varying circumferential distortions with different numbers of distortion cycles. These measurements are compared with two theoretical analyses. Clearly indicated is the existence of an unsteady cascade effect and the ability of the theories to adequately predict the trend of the unsteady response due to variations in reduced frequency, rotor stagger angle, solidity and mean incidence angle.