Cavitation is a complicated phenomenon in the centrifugal pump. In this work, the improved unsteady calculation model based on bubble-rotation-based Zwart–Gerber–Belamri (BRZGB) cavitation model is used to investigate the cavitation-vortex-pressure fluctuation interaction in a centrifugal pump under partial load with experimental validation. Spatial–temporal evolution of cavitation can be classified into three stages: developing stage, shedding stage, and collapsing stage. The cavitation evolution period is found as 1/4T (T is impeller rotation period), corresponding to the frequency 4fi (fi is impeller rotation frequency). On the analysis of the relative vorticity transport equation, it is revealed that the cavity is stretched by the relative vortex stretching term (RVS) and developed by the relative vortex dilation term (RVD), and they have great influence on the cavity shedding. The peak value of pressure fluctuation intensity occurs near the vapor–liquid interface at cavity rear, and shifts downstream with the cavitation development. The hysteresis between the vapor volume fraction, vorticity, and pressure fluctuation is observed, and the variation of vapor volume fraction is the source of cavitation-vortex-pressure interaction.
The multiphase rotodynamic pump is widely used in petroleum and gas exploitation, and blade tip clearance may cause flow instability and performance deterioration. In the present work, the influence of tip clearance on the transportation characteristic in a multiphase rotodynamic pump is investigated based on the non-uniform bubble model, in which the bubbles’ coalescence and break-up are considered. The influence mechanism of tip clearance on the energy performance is revealed. The results show that the leakage flow rate increases linearly with the increase in tip clearance, but variation in pump energy performance shows the opposite trend. In addition, a larger tip clearance results in a sharply decreased pressure increment in the impeller, while in the guide vane, the increment is raised slightly. For the 0 mm tip clearance condition, a positive vortex (relative to the impeller rotation direction) is observed in the impeller passage. However, the opposite leakage vortex is also found in the region near the tip clearance when the tip clearance is considered, and the vortex strength increases for a larger tip clearance.
In the chemical and petroleum industry, the axial flow pump is widely used for the circulation pipeline system, and most of the transportation mediums are the shear-thinning non-Newtonian fluids. However, previous investigations on axial flow pumps are focused on water, which leads to a considerable deviation between the actual application and the research finding. In this work, shear-thinning non-Newtonian fluid (CMC solution) and viscous Newtonian fluid (the viscosity equals the apparent viscosity of CMC solution as the flow index is 1) are selected as the working medium. Based on the research output, lower apparent viscosity occurs in the near-wall and rotor–stator interaction region due to the larger velocity gradient. The shear-thinning property results in an increased tip leakage flow rate, and a sharp decline in friction loss. Compared to the viscous Newtonian fluid, the head and efficiency of the pump improves substantially for the shear-thinning fluid. The discrepancy is observed to increase with a higher flow rate. The comprehensive analysis of flow field and energy performance reveals that friction loss is still the main part of the total loss in the shear-thinning fluid.
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