Numerical Simulation And Experimental Study Of Thermal Effect And Shedding Mechanism Of Cavitation In Liquid Nitrogen

Cavitation occurs in liquid flows when the local static pressure drops to a certain level below the saturation pressure where the liquid vaporizes into vapor and fills up the cavity.In high-thrust liquid hydrogen/liquid oxygen rocket propulsion systems,cryogenic fluid cavitation often occurs.Compared with normal temperature fluids,cryogenic fluids will be affected by thermal effects and produce obvious temperature gradients in the cavitation and nearby areas,making the development and collapse of cavitation significantly different from isothermal conditions.The research on cryogenic cavitation is in its infancy,especially the numerical simulation and experimental research related to the thermal effect and shedding mechanism of cryogenic fluid cavitation are not thorough enough.In this paper,a numerical simulation framework based on Realizable k-ε,Large Eddy Simulation(LES)turbulence model,and Schnerr-Sauer cavitation model is constructed,and the model is verified.The simulation and experimental results are in good agreement.In addition,the CFD numerical simulation of three-dimensional liquid nitrogen cavitation was carried out on a twisted hydrofoil,and liquid nitrogen cavitation under either thermal condition or isothermal condition(without considering the thermal effect)was simulated to explore the the influence of the thermal effect on the re-entrant jet mechanism of the cavitation shedding.The results show that,compared with the thermal effect cavitation in the same cavitation flow,isothermal cavitation has a higher shedding frequency and a larger cavitation length,indicating that the thermal effect inhibits the development of cavitation,and at the same time,the thermal effect changes the cavitation Shedding characteristics,the effect of the re-entrant flow becomes smaller,and the shedding of cavitation is mainly due to the interaction of cavitation and eddy currents.An experimental device for liquid nitrogen cavitation with a convering-diverging nozzle was built,and visualization experiments were carried out on the threedimensional venturi tube and the two-dimensional converging-diverging nozzle.The periodic shedding image of liquid nitrogen cavitation was obtained.The temperature drop in the cavitation zone was collected,and the influence of thermal effects on the inhibition of cavitation development was analyzed.The dimensionless parameters of the thermal effect are calculated.When the thermal effect becomes larger,the interval of cavitation collapse becomes shorter,and the development of cavitation is suppressed.The measurement of the point near the wall shows the negative fluid velocity,and the proportion of negative velocity particles and the effective number of particles are larger than the point near the center of the flow channel,which verifies the existence of the re-entrant flow and stagnation point.The experimental results are consistent with the mechanism of the cavitation shedding caused by the re-entrant flow as well as the formation mechanism of the re-entrant flow.