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

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