A Study on the Mechanism of Initiation and Propagation of Rotating Stall

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Flow mechanism which controls initiation and propagation of the rotating stall was studied by means of numerical simulation and experiment.A cascade of NACA65(12)10 blades with stagger angle 30ﾟ and solidity 1.0 was selected as an example for the study. When a blade stalls, a stall vortex is formed on the suction surface and then an unstall vortex near the trailing edge on the same suction surface. It is shown that these vortices restrict the flow through the blade channel and, as a result , cause stall of the neighbouring blade in the course of time-thus the stall propagates.Unstady pressure distribution on the surface of blades exposed to the rotating stall is also shown.Next, the initiation process of the rotating stall is analyzed, and the developing transient of the small disturbance until the completion of the steadily propagating large-auplitude rotating stall is shown.The experiment was carried out with the same blades as used in the numerical simulation placed at the test section of a linear cascade wind tunnel, and the unsteady pressure distribution on the blade surfaces is measured when the rotating stall is propagating. The purpose of the experiment is to confirm the availability of the simulation method by comparing both unsteady pressure distributions obtained each from the experiment and the numerical simulation.However, this purpose was not accomplished because the surface pressure data accurate enough to be compared with the numerical result could not be obtained, the main reason being that the adequate data averaging method was not found for the signals taken in the randomly fluctuating rotating stall flow. The experiment is planned to be continued.