小流量下尾水管锥管内流的PIV测试试验研究

PIV measurement of the flow with small discharge in a francis turbine draft tube

采用PIV激光内流测试设备对一个改进的HL220转轮模型试验所使用的尾水管锥管流场进行了测试,并对所测试各截面上的流场分布进行了详细的分析,研究了小流量工况下锥管径向面和子午面上的流场分布规律.结果表明:在小流量工况下,尾水管锥管内的瞬态流场呈现出明显的非定常特征,锥管中心处存在明显的回流,管壁处存在涡流;不仅小流量工况下的流场与最优工况下流场存在明显区别,小流量工况下瞬态流场与时均化流场的分布规律之间也存在一定的差异.PIV测试中采集收集的实验数据,有助于混流式水轮机小流量下尾水管非稳定性分析的内在机理研究,为CFD分析提供对比依据.

2-D laser particle image velocimetry（PlV） in-flow velocity measurement research was used to test various radial planes of a draft cone tube and its meridian planes for model test of an improved HL220 Francis turbine runner. Small discharge operating conditions was selected for the PIV velocity measurement. Analysis of the measurement result showed that under small discharge operating condition, the unsteady characteristic of the flow in the cone tube draft was evident and there existed obvi- ous reverse flow in the centre zone of the draft cone tube and swirls near the tube wall. The comparison of small discharge operating conditions, instantaneous flow distribution and the time-averaged flow indicated that there existed distinct difference between flow distribution under small discharge operating condition and flow distribution under the optimum operating condition. The distribution regulation between instantaneous flow distribution and time-averaged flow under small discharge operating conditions existed difference. The experimental data collected in PIV test provided reference for unsteady analysis for the inner mechanism of the flow with small discharge in a Francis turbine draft tube, and the comparison with CFD analysis.