凹坑缺陷对厚孔板喉部空化流动特性影响研究

Study on influence of pit defects on cavitation flow characteristics of throat of thick orifice plates

管道系统中的各类阀门、孔板等节流件,随系统工作前后压差的增大会出现水力空化现象,对系统的工作性能和安全造成严重影响。通过数值模拟探究了厚孔板空化的临界压比以及凹坑对孔板空化临界压比的影响,并进一步研究了凹坑与空化耦合作用下的空化流动特性,阐明了凹坑作用下的空泡溃灭机理。结果表明,只有当孔板出口压力与入口压力之比小于0.5时,才会发生空化。凹坑有促进空化气泡初生-发展-溃灭演变行为的作用,但压比在空化临界压比附近时,孔板各点压力峰值出现在无凹坑孔板以及存在凹坑缺陷孔板的无凹坑一侧。在液体管道和阀门的安全设计中,应考虑空化临界压比下气蚀的风险以及凹坑缺陷受空化剥蚀导致管壁减薄的危害。

Various valves,orifice plates and other throttling parts in the pipeline system will experience hydraulic cavitation as the pressure difference increases before and after the system works,which will seriously affect the working performance and safety of the system.The critical pressure ratio of cavitation of a thick orifice plate and the influence of pits on the critical pressure ratio of cavitation of an orifice plate were explored through numerical simulation.Furthermore,the cavitation flow characteristics under the coupling of pits and cavitation were further studied,and the mechanism of cavitation collapse under the action of pits was elucidated.The results show that cavitation occurs only when the ratio of orifice outlet pressure to inlet pressure is less than 0.5.The pit has the effect of promoting the primary-development-collapse evolution behaviour of cavitation bubbles,and a single small pit has almost no effect on the critical pressure ratio of cavitation,but the pit tends to increase the critical pressure ratio of cavitation.When the pressure ratio is near the critical pressure ratio of cavitation,the pressure peaks at each point appear on the pit side of the pit-free orifice plate and the pit side of the pit defective orifice plate,accompanied by periodic cavitation.In the safety design of liquid pipelines and valves,the risk of cavitation under the cavitation critical pressure ratio and the hazard of pipeline wall thinning caused by cavitation and ablation of pit defects should be considered.