水泵水轮机甩负荷过渡过程中脉动压力的模拟

Simulation of pressure fluctuation of a pump turbine in load rejection

水泵水轮机甩负荷过渡过程中脉动压力幅值较大,甚至可达近百米,但一维数学模型计算所得为均值压力,即水击压力,无法模拟脉动压力。工程设计中通常依据经验确定脉动压力极值的变化范围,但无从考虑不同水泵水轮机、甩负荷不同工况轨迹线的对脉动压力的影响。为此本文利用水泵水轮机模型试验脉动压力等值线图,并结合甩负荷工况轨迹线对脉动压力的幅值进行预测,结果表明预测值与实测值的波形基本一致。该方法不仅能较准确地模拟由水击压力和脉动压力构成的总动水压力,而且有利于导叶关闭规律的优化,即优化甩负荷工况轨迹线,避开脉动压力最严重的区域(大开度飞逸点附近区域),使得总动水压力极值最小。

The amplitude of pressure fluctuation of a pump turbine in load rejection is larger than that of a conventional Francis turbine, even up to nearly 100 meters. The one-dimensional mathematical model will give mean pressure rather than pressure fluctuation. In engineering design the range of pressure fluctuations is usually estimated based on experience, and such estimation is unable to take into account the pressure fluctuation differences in different pump turbines or different condition trochoids of load rejection. This paper attempts to estimate fluctuation amplitude, using the contour lines of pressure fluctuations of a model pump turbine along with its condition trochoids of load rejection. The results so obtained show an agreement of the estimated wave forms to those of prototype measurements. This method is not only useful for calculation of total hydrodynamic pressure through adding a fluctuation component to mean pressure （i.e. water hammer pressure）, but it favors optimization of guide vanes closing. In the latter case, the operation with optimized condition trochoids of load rejection can avoids the worst regions of pressure fluctuation （i.e. the regions near the runaway points of large openings）, thus obtaining the minimum of total hydrodynamic pressure extremum.