Numerical Study on Rotating Stall in Finite Pitch Cascades

Flow behavior of rotating stall in finite pitch cascades is discussed through numerical analyses by means of a vortex method, which is particularly developed to solve unsteady flows through stalled cascades. It is shown that stall vortex and unstall vortex are, shed from each stalled blade periodically, and the behavior of these vortices has considerable effects on various properties of rotating stall, such as magnitude of flow fluctuation, propagation velocity, the number of stall cells, and so on. When a rotating stall is initiated and developed in an isolated cascade at smaller inlet flow angles around the stall inception point, a plural number of stall cells tend to propagate on the growing process, although only one stall cell survives eventually in a fully developed rotating stall. At larger flow angles, a single stall cell splits into two separate cells as it propagates. These processes are found for the first time through the analyses of finite pitch cascades. With the inlet guide vanes upstream, a plural number of stall cells can grow in a fully developed rotating stall, and the number of stall cells depends on the exit flow angle of the guide vanes and the axial distance between the two cascades. The numerical results agree well with experiments.