栅中空化水翼的水动力特性

EXPERIMENTAL INVESTAGATIONS ON THE DYNAMIC OF CAVITATING FLOW AROUND A CASCADE OF HYDROFOIL

采用实验的方法研究了栅中水翼的空化水动力特性。实验在空化水洞中完成,采用高速摄像技术观测了不同空化阶段的空穴形态,并测量了栅中水翼所受的升阻力。结果表明:在空化没有发生时,栅中水翼所受升阻力随雷诺数的增加而增大;当空化产生时,不同的雷诺数下栅中水翼空化动力特性随σ/2α的变化趋势一致;在相同的雷诺数下,当4>σ/2α>2.8时,栅中水翼升力系数变化的频率基本不随σ/2α改变,最大空穴长度小于水翼弦长,此时St=0.11;当σ/2α<2.8时,栅中水翼升力系数变化的频率增加,对应的St=0.28。

The flow structure and the dynamics of cavitating flow in a cascade of hydrofoil are investigated experimentally. Experiments are conducted in a cavitation tunnel and situations ranging from non cavitation to unsteady cloud cavitation are obtained by varying the Reynolds number and the cavitation numbers. The instantaneous shapes of the cavity are observed by high-speed video and high-speed photo. The frequency of cavitating oscillation is obtained by the lift/drag measurements. From the results of experiments, the lift/drag of the hydrofoil increases with increasing the Reynolds number in cavitating flow. When the cavitation number is decreased, it is found that two distinct cavity self-oscillation dynamics characterized by mainly responsible for the cavity breakdown. At 4 〉σ/2α〉 2.8, a low frequency shedding of cloud cavitation results in a strong oscillation in lift at a Strouhal number, based on chord length, of about 0.11. This frequency is relatively insensitive to changes in a. As σ/2α〈 2.8, cavity lengths exceed the foil chord, the growth breakdown cycle of the cavity is observed at a higher Strouhal number, of about 0.28.