减速运动活塞表面压力计算及空化初生预测

Calculation of pressure on decelerating piston surface and cavitation incipience prediction

为了预测空化初生，用特征线法计算了减速运动活塞前管内一维非定常流的压力变化及分布，分析了管内压力变化规律及空化初生的条件。作为对照观察了液体中作减速运动活塞表面的空化现象，发现活塞在导管中做减速运动时，其表面压力下降。活塞前水柱愈长，活塞表面压力愈低。撞击骤停的活塞体基本上按线性变化的加速度减速，加速度变化斜率愈大，活塞表面在停止时所达到的压力愈低，加速度变化斜率趋于无穷时，该压力趋于确定的极限值。提出使用测量液体中运动物体的加速度来预测空化初生，以便监测装置运行。

To predict cavitation incipience, pressure wave and distribution of one dimensional unsteady flow before piston moving in pipe were calculated by the method of characteristics. Pressure characteristics and condition of cavitation incipience were analyzed. Calculation result was compared with cavitation observation on surface of decelerating piston. It is found that pressure at decelerating piston surface drops when it moves in liquid. The longer water column before piston, the lower pressure on the piston surface. Piston decelerates in roughly linear acceleration in collision. The steeper slope of acceleration increases, the lower pressure piston surface bears at stop. When the slope tends to be infinite, piston surface pressure reaches a limited value. Method of measuring the acceleration of moving submerged body is proposed to predict cavitaion incipience and monitor operating instruments.