Modelling of Separated Flow around Oscillating Cascades by Classical Singularity Method

A simple and fast method is presented which constitutes a first step towards calculating unsteady airloads on oscillating compressor blades with separated flow on the suction side of the blades. The oscillations of the cascade are specified and are assumed to be fundamental. The blade profiles are replaced by flat plates. Both steady loading and turning are neglected. Furthermore it is also assumed, that the separation points and the reattachment points at the suction side of the blades are defined and fixed. The separation bubbles therefore do not move, and the flow is separated during the whole cycle of oscillation. The flow is assumed to be inviscid, isentropic and purely subsonic. With these simplifications made, the problem can be treated with the linearized potential theory. Results of the method are presented and compared with the calculations of M. R. Chi, who made a very similar approach to solve the problem, but deduced the governing system of equations in a different way. Regions of agreement were found but also regions of significant differences, which have to be investigated more thoroughly in the future.