Unsteady forces on annular cascade blades in subsonic flow with swirl

The effect of mean flow swirl on unsteady response of unloaded annular cascade subject to an incident convected disturbance is examined as a model for a compressor stage flow. The concept of a generalized gust is introduced which describes the evolution of an upstream nearly-convected perturbation to the point of its interaction with downstream cascade. The correspondence to classical gust definition is established followed by comparison of predicted unsteady forces with two-dimensional cascade results. In Region I corresponding to IGV/rotor interaction with a 26.6 degrees swirling wheel flow, the effect of swirl on the amplitude of cascade unsteady response is limited to the change of the far held radiation conditions. In contrast, in Region II corresponding to rotor/stator interaction with a 45 degrees mixed swirling flow, a remarkable amplification of the upwash component of the gust is noted. The predicted increment of cascade unsteady lift is obtained as a function of the generalized gust evolution distance.