弥合性水击弛豫计算方法及其射流-缓冲机理分析

Relaxation Calculation Method and Analysis of Jet-Buffer Mechanism in Water Hammer with Liquid Column Separation

为分析弥合性水击中的射流-缓冲机理,建立了能够实现自适应过程的多相弛豫计算方法,并通过水气两相激波管验证了该计算方法的合理性及稳定性。对弥合性水击中的内部流动机理进行分析,结果表明:对于二次压力变化值高于理论计算值的弥合性水击,其流动按规律可以分为直接水击阶段、缓冲水击阶段和射流水击阶段;在缓冲水击阶段,空穴泡粒的存在降低了初次水击对边界处的压力冲击,使得水击呈现被缓冲状态,压力变化值小于理论计算值;在射流水击阶段,空穴压缩溃灭时产生的射流加速并未直接作用于初次水击对边界处的压力冲击,而是经过反向传播后,在初次水击基础上造成二次压力变化,该变化值高于理论计算值。射流水击的出现,影响了采用直接水击方法计算压力升高值的准确度,因此这也是弥合性水击中最应该注意的部分。

A multiphase relaxation calculation method with the adaptive process was established to analyze jet-buffer mechanism in water hammer with liquid column separation.The rationality and stability of this calculation method were verified by air-water two-phase shock tube.The internal flow mechanism of water hammer with liquid column separation was analyzed.The results show that for water hammer with liquid column separation whose seco-ndary pressure variation value is higher than the theoretical ones,it can be divided into the direct water hammer,the buffer water hammer,and the jet water hammer.In the stage of buffer water hammer,the presence of bubbles reduces the pressure impact on the boundary,causing the water hammer wave appear buffered and the change of pressure value is smaller than the theoretical ones.In the stage of jet water hammer,the jet acceleration generated during void compression and collapse does not directly affect the pressure impact on the boundary,but it causes a secondary pressure change accumulation in the initial value after back propagation,and the change value is higher than the theoretical calculation value.The occurrence of jet water hammer affects the accuracy of value calculated by direct water hammer method,so this is the most noteworthy part of water hammer with column separation calculation.