关键词: 计算流体力学, 液氮, 超声空化, 气液两相流, 动态建模, 空化数

Abstract:

Based on the computational fluid dynamics (CFD) and experimental method, the cavitation characteristics of liquid nitrogen induced by ultrasonic waves with a frequency of 20 kHz are studied. The simulations were based on the mixture model with the Singhal cavitation model for phase change calculations, and the Realizable k-ε turbulence model was adopted for turbulence consideration. The sinusoidal oscillation of the vibrator was realized with the dynamic mesh method to simulate the ultrasonic generator. The periodic variation characteristics of the ultrasonic cavitation structure were obtained, which are in good agreement with the experimental observations. Based on the CFD models, the changes of pressure and temperature in the ultrasonic affected zone were obtained to make up for the lack of experimental conditions. It was found that the ultrasonic cavitation of liquid nitrogen had different characteristics due to the thermal effect compared with ultrasonic cavitation of water. The effects of different amplitudes, ultrasonic frequencies and pressures of cavitation were studied. The expression of the ultrasonic induced cavitation number was proposed, and the result proved that the smaller the cavitation number, the more likely to occur cavitation and the larger the cavity. The results reveal the mechanism of liquid nitrogen ultrasonic cavitation.

Key words: CFD, liquid nitrogen, ultrasonic cavitation, gas-liquid flow, dynamic modeling, cavitation number