Research on pressure fluctuation induced by tip leakage vortex of axial flow circulating pump under unpowered driven conditions

Axial flow circulating pumps (AFCPs) are large marine steam turbine units for large-sized ships. One peculiar operation condition for AFCPs is when a ship cruises beyond a certain speed, the energy of pump inflow can completely overcome the frictional resisting moment of the pump itself, thereby driving the impeller to rotate. Such a condition is also known as the unpowered driven condition (UDC). At this time, the fluid is in the artesian flow state. In this paper, pressure fluctuation and inner flow of the AFCP under UDCs and different inflow conditions are analyzed using delayed detached-eddy simulation turbulence model. It is found that the intensity of the tip leakage vortex (TLV) decreases from the leading edge to the trailing edge of the blade, and the amplitude of pressure pulsation caused by TLV also decreases. Due to the jet wake structure at the blade trailing edge, the amplitude of pressure fluctuation at the trailing edge of the blade increases by 7.8% under the optimal UDC. In addition, the compression-expansion term determines the strength of the core of TLV, thus affecting the amplitude of pressure fluctuation. The viscous dissipation effect of TLV can cause high-frequency components of pressure fluctuation.