立軸斜流ポンプ羽根車に働く軸スラストの挙動

Abstract

Axial thrust forces acting on an impeller of a diffuser type mixed flow pump have been studied. The behavior of the axial thrust generated by the vortex occurrence in a pump intake sump was investigated. The thrust of distinct discontinuities such as hysteresis phenomenon from a pump hydraulic performance was measured. In pump partial load operation the axial thrust increases discontinuously because of the reverse flow at impeller inlet. Synchronous and non-synchronous components of axial thrust increase during the onset of reverse flow zones. A prediction method for static axial thrust was derived based on Oshima's theory accounting for the pump suction bell-mouth pressure reduction due to vortex. Qualitative comparison with the measured experimental results for static axial thrust showed reasonable agreement around pump best efficiency flow rate. The pump intake sump test apparatus，in which both an air-entrained surface vortex and a submerged vortex will occur，was employed and the axial thrust was measured. The level of axial thrust is dependent on the pump intake sump water level. The dynamic axial thrust begins to increase due to the occurrence of a full air core vortex to intake. When submerged as well as full air core continuous vortices occur，the axial thrust and the fluctuation of total pump head become abruptly large. The fluctuation of axial thrust becomes the highest when the impeller sucks the air-drawing large vortex imposing a pressure fluctuation which generates not only a rotational speed but also nZ vane passing and low frequency components.