Cavitation occurs in the micro-clearance of liquid-hydrogen-lubricated bearings owing to the pressure drop caused by high-speed shearing.The pressure undulation caused by cavitation collapse results in bearing surface...Cavitation occurs in the micro-clearance of liquid-hydrogen-lubricated bearings owing to the pressure drop caused by high-speed shearing.The pressure undulation caused by cavitation collapse results in bearing surface erosion and significantly affects the bearing performance.In this study,a modified Z-G-B cavitation model was used to study the crushing process of a single liquid hydrogen bubble in a shear micro-clearance.Fast Fourier transform(FFT)and wavelet transform(WT)were applied to study the frequency characteristics of the pressure,mass transfer rate,and vapor mass fraction during bubble rupture in shearing micro-clearance.To obtain a deeper insight into the details of the effect of the shear micro-clearance structure on bubble collapse,the relationship between the flow field energy,attenuation rate,and frequency was investigated.The proper orthogonal decomposition(POD)and dynamic mode decomposition(DMD)methods were used to analyze the energy of each order mode of the flow field.The analysis results of the bubble vibration intensity with respect to time and frequency provide a theoretical basis for the optimization of the bearing structure.展开更多
In the micro-clearance of the valves and sealing structures of liquid hydrogen(LH2)storage tanks,bubbles occur due to heat leakage.The sudden rising of pressure causes bubbles to collapse,resulting in pressure and tem...In the micro-clearance of the valves and sealing structures of liquid hydrogen(LH2)storage tanks,bubbles occur due to heat leakage.The sudden rising of pressure causes bubbles to collapse,resulting in pressure and temperature fluctuations that impact the sealing surface and the valve.In this paper,the cryogen cavitation model is modified by considering the thermal effect,surface tension,and viscosity.The bubble collapse inside micro-clearance is investigated by the modified cavitation model and volume of fluid(VOF)method.Transient pressure and temperature at the bubble center during collapse are recorded and evaluated.The effects of micro-clearance height,dimensionless bubble diameter,and bubble vertical position on bubble collapse and bubble morphology are investigated.To reduce the cavitation erosion on the walls,the frequency and time-frequency characteristics of the pressure oscillations induced by bubble collapse are analyzed by Fast Fourier Transform(FFT)and Wavelet Transform(WT).Furthermore,the temperature and pressure field variation and oscillation mechanisms are analyzed by Proper Orthogonal Decomposition(POD)and Dynamic Mode Decomposition(DMD).The analytical results reveal the LH2 bubbles collapse mechanism within the micro-clearance.The results provide a certain extent of reference for optimizing the structure of micro-clearance.展开更多
基金National Natural Science Foundation of China(Grant No.:51976150)China Postdoctoral Science Foundation(Grant No.:2021M692533)Youth Innovation Team of Shaanxi Universities.
文摘Cavitation occurs in the micro-clearance of liquid-hydrogen-lubricated bearings owing to the pressure drop caused by high-speed shearing.The pressure undulation caused by cavitation collapse results in bearing surface erosion and significantly affects the bearing performance.In this study,a modified Z-G-B cavitation model was used to study the crushing process of a single liquid hydrogen bubble in a shear micro-clearance.Fast Fourier transform(FFT)and wavelet transform(WT)were applied to study the frequency characteristics of the pressure,mass transfer rate,and vapor mass fraction during bubble rupture in shearing micro-clearance.To obtain a deeper insight into the details of the effect of the shear micro-clearance structure on bubble collapse,the relationship between the flow field energy,attenuation rate,and frequency was investigated.The proper orthogonal decomposition(POD)and dynamic mode decomposition(DMD)methods were used to analyze the energy of each order mode of the flow field.The analysis results of the bubble vibration intensity with respect to time and frequency provide a theoretical basis for the optimization of the bearing structure.
基金supported by the National Natural Science Foundation of China(Grant No.51976150)the Youth Innovation Team of Shanxi Universities。
文摘In the micro-clearance of the valves and sealing structures of liquid hydrogen(LH2)storage tanks,bubbles occur due to heat leakage.The sudden rising of pressure causes bubbles to collapse,resulting in pressure and temperature fluctuations that impact the sealing surface and the valve.In this paper,the cryogen cavitation model is modified by considering the thermal effect,surface tension,and viscosity.The bubble collapse inside micro-clearance is investigated by the modified cavitation model and volume of fluid(VOF)method.Transient pressure and temperature at the bubble center during collapse are recorded and evaluated.The effects of micro-clearance height,dimensionless bubble diameter,and bubble vertical position on bubble collapse and bubble morphology are investigated.To reduce the cavitation erosion on the walls,the frequency and time-frequency characteristics of the pressure oscillations induced by bubble collapse are analyzed by Fast Fourier Transform(FFT)and Wavelet Transform(WT).Furthermore,the temperature and pressure field variation and oscillation mechanisms are analyzed by Proper Orthogonal Decomposition(POD)and Dynamic Mode Decomposition(DMD).The analytical results reveal the LH2 bubbles collapse mechanism within the micro-clearance.The results provide a certain extent of reference for optimizing the structure of micro-clearance.
