2019 Volume 12 Issue 4 Pages 430-438
In many industrial processes such as natural gas processing, seawater desalination et al, there is a large amount of liquid waste pressure energy, which can be converted into electric or mechanical energy by a micro-hydraulic turbine. But its efficiency and stability will deteriorate when the working fluid contains gas. Aiming at improving the hydraulic efficiency of the micro-turbine, the three-dimensional transient two-phase flow model which adopts the shear-stress-transport (SST) model as turbulence model and Eulerian-Eulerian model as two-phase flow model with the commercial code ANSYS-CFX was established and solved to study the two-phase flow characteristics of the micro-hydraulic turbine with fixed guide vane openings under different gas volume fraction (GVF). The numerical simulation results show that the power and efficiency of the turbine decrease by 24% and 21% respectively when the inlet GVF is 0.20. The area of low pressure in each impeller passage increases with the inlet GVF, and the pressure difference between the working and suction surface of the blade decreases. The GVF distribution in impeller passage is asymmetrical, which is caused by the gas-liquid separation in the volute. At the left lower part of impeller passage, the gas accumulates at the suction surface of the blades under the Coriolis force and its GVF reaches 90%. The asymmetrical GVF distribution will result in the asymmetrical pressure distribution in the impeller passage, which leads to the imbalance force on the blades. Moreover, the asymmetrical GVF distribution will reinforce the positive incidence at the lower part of impeller passage, and weaken it at the upper right impeller passage. The volute should be redesigned to ensure the uniform gas distribution at the inlet of each impeller passage.
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