Unsteady Stress of 4-Bladed Inducer Blades and the Effect of Inlet Flow Distortion.

Abstract

Unsteady stress of 4-bladed inducer blades was measured with and without inlet flow distortion at the blade root near the leading edge. The following results were obtained : (1) Without the inlet flow distortion, and with the alternate blade cavitation at intermediate cavitation number, the mean stress of the blade with shorter cavity is lower than that with longer cavity. At lower cavitation number, the stress fluctuation occurs caused by the cavitation instabilities such as rotating cavitation and cavitation surge, which is one of the major causes of stress fluctuation of inducers. (2) The magnitude of stress fluctuation due to the interaction with the inlet flow distortion basically decreases as we decrease the cavitation number. With inlet flow distortion, the occurrence ranges of alternate blade cavitation and cavitation instability shift toward the lower cavitation number. Under the alternate blade cavitation, the fluctuation of longer cavity causes the stress fluctuation of the adjacent blade with shorter cavity. The stress fluctuations caused by the rotating cavitation and cavitation surge are neary the same level as those in case without inlet flow distortion.