自激脉冲空化喷嘴三维非稳态流动的数值模拟

Numerical simulation of self-excited pulsed cavitation nozzle in three-dimensional unsteady flow

选择RNG k-ε、Realizable k-ε、标准k-ω和SST k-ω这4种湍流模型,对低压自激脉冲空化射流喷嘴内部流场进行数值模拟研究,验证其对脉冲空化喷嘴内部三维非定常流场模拟的适定性,研究表明RNG k-ε模型的模拟精度高且易收敛,网格无关性验证和时间步长分析说明应尽量减少时间步长.基于三维非稳态空化模型,考虑重力因素,对喷嘴腔室内部流场进行了数值分析,通过压力、速度、水蒸气体积分数和温度的分布云图,分析了1个周期内腔室内部空化初生、能量集中和释放的演变过程,解释了空化射流的产生机理,与试验结果对比,验证了腔室内部流场演变的正确性,考虑重力因素,进行喷嘴内部流场三维模拟更加符合工程实际.

Four turbulent models of RNG k-ε,Realizable k-ε,k-ωand SST k-ωwere employed to simulate the internal flow field of lowpressure self-excited pulsed cavitation jet nozzle and then the well-posedness of the selected models were verified.The simulation results of three-dimensional unsteady flow field inside the nozzle show that the RNG k-εturbulence model can simulate the pulse flow of cavitation nozzle accurately and it is easy to converge.Grid independence and time step optimization are also presented that time step can be as minor as possible.The gravity factor is taken into account to carry out the evolution process of the interior flow in one cycle by using the dynamic variables of pressure,velocity,water vapor volume fraction and temperature during the cavitation inception,energy concentration and energy release.The occurrence mechanism of the low pressure and large flux selfexcited pulsed cavitation jet and the flow field evolution characteristics are also illustrated.Comparing the numerical simulation with the experimental results,it is verified that the selected turbulence model is appropriate and the evolution of the flow in the chamber is reliable.Considering the influence of gravity,the simulation results in the nozzle more coincide with the actual situation in the engineering practice.