Numerical simulation on influence of tooth clearance on twin screw turbine leakage
CAO Ling1, JIANG Xiaoping1,2*, PAN Huishan1,ZHOU Chenjia1
1. National Research Center of Pumps, Jiangsu University, Zhenjiang, Jiangsu 212013, China; 2. National Engineering and Technology Center for Information Agriculture, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China
Abstract：In order to reduce the effect of leakage flow on the twin screw hydraulic turbine efficiency,the two-thirds of tooth of double screw pump as turbine was selected. Firstly, simplified geometric mo-del was established according to the principle of twin screw pump inner clearance between teeth. A mathematical model of the leak path between the teeth was built by using the theory of the shear flow caused by relative motion in turbine cavity and differential pressure flow caused by differential pressure of the chamber at all levels. SCORG and Pumplinx software were used to conduct full flow field numerical simulation on the twin screw hydraulic turbine, and the flow field distribution and flow rate variation law were obtained under different tooth clearances of the twin screw turbine. The results show that the screw pressure distribution law under different clearances is basically consistent, the pressure distribution in each sealing chamber is basically uniform, and the pressure in each adjacent chamber from the inlet to the outlet presents a linear downward trend. There are several leakage channels near the clea-rance between the screw teeth. Under the action of the pressure difference of each chamber, there is no obvious high velocity zone in the first stage of the cavity, and obvious high-speed leakage occurs from the second stage of the cavity. With the increase of the gap between teeth, leakage area and leakage rate of tooth-side clearance in the same cavity increase. The fluid leakage from the inlet to the outlet and volume loss increase as well. When tooth clearance are 0.04 and 0.08, 0.12, 0.16 and 0.20 mm, the volume losses caused by the clearance are 4.03%, 4.57%, 5.00%, 5.43% and 5.72% respectively.
