Fluctuating Hydraulic Force Around a Centrifugal Impeller Due to Inlet Flow Distortin and Whirling Motion

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Unsteady flow behavior in the space between the pump suction casing and the centrifugal impeller side shroud was investigated, to know the fluctuating hydraulic force due to inlet flow distortion and whirling motion. The following results were mainly carried out.(1)The unsteady core of the inlet swirling flow makes the impeller whirling motion.(2)The inlet distortion affects strongly the impeller outlet flow. Its effect is extreamly when the swirling direction is negative to the impeller rotation, and the periodical flow fluctuation given by the blade number becomes heavy at the outlet section.(3)Its fluctuation is conducted to the space between the suction casing and the impeller side shoroud, and causes not only the unsteady axial thrust but also the swirling motion.(4)The fluctuating pressure value in the space becomes to change in the peripheral direction with increasing the pumping discharge. This penomenon makes the impeller rotation flutter motion.(5)Above fluctuation lies on another fluctuation induced from the whirling motion of the impeller. The latter fluctuation is sharp in close to the impeller ring.(6)The avaraged pressure distribution in the radial direction can be predicted roughly with the steady rotating disk model in the cylinder.