液氮空化流动的实验和数值计算研究

Experimental and Numerical Simulation of Cavitating Flows in Liquid Nitrogen

本文采用实验和数值计算相结合的方法针对低温液氮的空化流动特性进行了研究。本实验在低温介质空化流动测试平台中完成,采用高速全流场显示技术观测了温度为77.6 K的液氮在收缩-扩张管内的空穴形态并同步采集了流量:和空穴内部的压力数据。分别采用LES湍流模型和基于密度比修正的DCM湍流模型数值模拟了液氮的非定常空化流动。实验结果表明:液氮空化流动的非定常特性显著,单次完整地脱落周期约为3 ms,空穴呈现模糊状且不易溃灭。由于热力学效应的影响,空穴内部的局部压力低于来流温度下的饱和蒸汽压。数值结果表明:两种湍流模型计算得到的时均压力分布和非定常空穴形态与实验结果吻合良好,均能较好的描述液氮空化流动过程中空穴的形态和空化变化的准周期特性。与LES湍流模型结果相比,DCM湍流模型计算得到的云状脱落空泡团尺寸较大,空穴界面更加清晰。LES计算得到的空穴形态比较模糊,与实验结果更加接近。

The experiment and numerical simulation are both performed to investigate the characteristics of unsteady cavitating flows in liquid nitrogen.The experiment was conducted in the cryogenic cavitating flows test platform and a high-speed video camera was employed to obtain the unsteady evolution of cavitating flows through the convergent-divergent nozzle.In addition,the pressure distributions at cavitation region and the flow rate were collected synchronously.The large-eddy simulation(LES) and the density-corrected turbulence model(DCM) were used respectively to calculate the unsteady cavitating flows.The experiment results show that the unsteady characteristics of liquid nitrogen cavitating flows are significant.The complete shedding cycle of the cloud cavity is about 3 ns and the cavity structure is indistinct and hard to collapse.Due to the thermodynamic effects,the measured pressure at cavity region is lower than that of free-stream liquid.The numerical results show that the predicted cavity structure,the quasi-periodic characteristics of cavitation and pressure inside cavity by two turbulence model agrees well with the experimental data.Compared with the results calculated by large-eddy simulation,the shedding cloud cavity predicted by DCM model is larger and the cavity interface is clearer.The cavity structure simulated by LES is indistinct,which agrees well with the experimental observation.