Numerical And Experimental Study Of The Effect Of Ultrasonic Parameters On Cavitation Of LN2

Cavitation phenomena is an inevitable problem in rocket cryogenic pumps,and cavitation corrosion is becoming one of the main considerations in the design of turbine pumps.Ultrasonic cavitation is generated by an ultrasonic generator in liquid nitrogen,which converts acoustic energy into a concentrated source of excitation fluctuation pressure and generates active cavitation to study the cryogenic cavitation erosion characteristics.Since the thermal effect of cryogenic fluids is more complicated than that of room-temperature fluids such as water,and the measurement is more difficult,and there is still a lack of experimental data and fewer numerical models reported in the literature,cryogenic ultrasonic cavitation is still in its infancy in the field of cryogenic cavitation.In this paper,using a combination of numerical simulations and experimental studies,the occurrence laws and physical characteristics of liquid nitrogen ultrasonic cavitation phenomena were investigated.The main work was as follows.1.A single bubble dynamic model of liquid nitrogen ultrasonic cavitation with thermal effect was developed.With the help of MATLAB software,the dynamic analysis was carried out.The single bubble growth and collapse laws were used to analyze the mechanism characteristics of the cavitation zone and explain the difference between ultrasonic cavitation of liquid nitrogen and normal temperature fluid.The simulations were based on the Mixture model,the Singhal cavitation model and the Realizable k-ε turbulence model,and the sinusoidal oscillation of the vibrator was realized with the dynamic mesh method.With the help of FLUENT software,the ultrasonic cavitation is simulated to produce a cavitation zone in liquid nitrogen and to obtain the evolution of temperature,pressure and gas phase content distribution in the flow field around the oscillator.2.Based on the numerical model,the effects of relevant ultrasonic parameters such as oscillator amplitude,ultrasonic frequency and system pressure on the ultrasonic cavitation characteristics of liquid nitrogen were investigated.The variation law of cavitation zone and the growth law of single bubble under different amplitudes,different ultrasonic frequencies and different system pressures were obtained by numerical calculations.The expression of ultrasonic-induced cavitation number was improved to reveal the influence of relevant parameters on cavitation flow generation.3.A set of visualized liquid nitrogen ultrasonic cavitation experiment set-up was built,which mainly consisted of the main body of the experimental table,ultrasonic generator,liquid nitrogen supply system,vacuum system and measurement system.It can be used to record the bubble growth and collapse process and to verify the numerical calculation results.The experiments of liquid nitrogen ultrasonic cavitation were carried out under different power conditions to obtain the effects on the liquid nitrogen ultrasonic cavitation characteristics,which were compared and analyzed with the numerical calculation results.