Based on the Reynolds-Averaged Navier-Stokes equations and mass transfer model, an approach, where a three-component cavitation model is proposed, is presented to simulate ventilated cavitating flow as well as natural...Based on the Reynolds-Averaged Navier-Stokes equations and mass transfer model, an approach, where a three-component cavitation model is proposed, is presented to simulate ventilated cavitating flow as well as natural cavitation. In the proposed cavitation model, the initial content of nucleus in the local flow field is updated instantaneously, and is coupled with the Rayleigh-Plesset equation to capture the cavity development. The proposed model is applied to simulate the cavitating flow around an under-water vehicle in different cavitation conditions. The results indicate that for the natural and ventilated cavitation simulation, the predicted cavitation characteristics including the cavity length, cavity diameter and cavity shape agree satisfactorily with the analytic and experimental results, for the ventilated cavitation, the proposed methods reproduce the special behavior that the axial line of the cavity bends and rises at the tail part. The study concludes that the ventilated flow rate of the non-condensate gas influences the development of natural cavitation as well as ventilated cavitation, and the vapor cavity is suppressed remarkably by the gas cavity with the increase of the gas ventilation.展开更多
A series of projectile and water-tunnel experiments were conducted to investigate the shape characters of natural and ventilated supercavitation. It was found that the shape and dimensions of both the natural supercav...A series of projectile and water-tunnel experiments were conducted to investigate the shape characters of natural and ventilated supercavitation. It was found that the shape and dimensions of both the natural supercavitation and the ventilated supercavitation are similar through the comparison of them when the cavitation number is small and equal, and the contour of both the natural supercavitation and the ventilated supercavitation can be calculated effectively with the Savchenko formula. The gravity effect can induce the asymmetry of ventilated supercavitation, and the asymmetry is more apparent as the Froude number is smaller. The empirical formula for calculating the axial deformation of ventilated supercavitation was corrected and expanded based on experiment data. The evolution rules of both the natural supercavitation and the ventilated supercavitation were described, and the vortex frequency of natural cavitation was obtained. In addition, the hysteretic aspect was observed between the development and the fall process of ventilated cavitation.展开更多
When a body navigates with cavity in shallow water, both flexible free surface and rigid bottom wall will produce great influences on the cavity shape and hydrodynamic performances, and further affect the motion attit...When a body navigates with cavity in shallow water, both flexible free surface and rigid bottom wall will produce great influences on the cavity shape and hydrodynamic performances, and further affect the motion attitude and stability of the body. In the present work, characteristics of the natural cavitating flow around a 2-D symmetrical wedge in shallow water were investigated and the influences of two type boundaries on the flow pattern were analyzed. The Volume Of Fluid （VOF） multiphase flow method which is suitable for free surface problems was utilized, coupled with a natural cavitation model to deal with the mass-transfer process between liquid and vapor phases. Within the range of the cavitation number for computation （0.07-1.81）, the cavity configurations would be divided into three types, viz., stable type, transition type and wake-vortex type. In this article, the shapes of the free surface and the cavity surface, and the hydrodynamic performance of the wedge were discussed under the conditions of relatively small cavitation number （〈0.256）. The present numerical cavity lengths generally accord with experimental data. When the cavitation number was decreased, the cavity was found to become longer and thicker, and the scope of the deformation of the free surface also gradually extends. The free surface and the upper cavity surface correspond fairly to their shapes. However, the lower side of the cavity surface was rather leveled due to the influence of wall boundary. The lift and drag coefficients of this 2-D wedge basically keep linear relations with the natural cavitation number smaller than 0.157, whereas direct proportion for drag and inverse proportion for lift.展开更多
The present simulation investigates the multiphase cavitating flow around an underwater projectile.Based on the homogeneous equilibrium flow assumption,a mixture model is applied to simulate the multiphase cavitating ...The present simulation investigates the multiphase cavitating flow around an underwater projectile.Based on the homogeneous equilibrium flow assumption,a mixture model is applied to simulate the multiphase cavitating flow including ventilated cavitation caused by air injection as well as natural cavitation.The transport equation cavitating model and a local linear low-Reynolds-number turbulence model are incorporated to the equation system.The calculations are executed based on a suite of computational fluid dynamics code.The hydrodynamics characteristics of flow field under the interaction of natural cavitation and ventilated cavitation are analyzed.The results indicate that the ventilated cavitation numbers and the drag coefficient are relative to the natural cavitation numbers and gas flow rate in the multiphase cavitating flows.展开更多
The present simulation investigates the multiphase cavitating flow around an underwater projectile.Based on the Homogeneous Equilibrium Flow assumption,a mixture model is applied to simulate the multiphase cavitating ...The present simulation investigates the multiphase cavitating flow around an underwater projectile.Based on the Homogeneous Equilibrium Flow assumption,a mixture model is applied to simulate the multiphase cavitating flow including ventilated cavitation caused by air injection as well as natural cavitation that forms in a region where the pressure of liquid falls below its vapor pressure. The transport equation cavitating model is applied.The calculations are executed based on a suite of CFD code.The hydrodynamics characteristics of flow field under the interaction of natural cavitation and ventilated cavitation is analyzed.The results indicate that the ventilated cavitation number is under a combined effect of the natural cavitation number and gas flow rate in the multiphase cavitating flows.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 50976061, 50676044)the Natural Science Foundation of Beijing (Grant No. 3072008)
文摘Based on the Reynolds-Averaged Navier-Stokes equations and mass transfer model, an approach, where a three-component cavitation model is proposed, is presented to simulate ventilated cavitating flow as well as natural cavitation. In the proposed cavitation model, the initial content of nucleus in the local flow field is updated instantaneously, and is coupled with the Rayleigh-Plesset equation to capture the cavity development. The proposed model is applied to simulate the cavitating flow around an under-water vehicle in different cavitation conditions. The results indicate that for the natural and ventilated cavitation simulation, the predicted cavitation characteristics including the cavity length, cavity diameter and cavity shape agree satisfactorily with the analytic and experimental results, for the ventilated cavitation, the proposed methods reproduce the special behavior that the axial line of the cavity bends and rises at the tail part. The study concludes that the ventilated flow rate of the non-condensate gas influences the development of natural cavitation as well as ventilated cavitation, and the vapor cavity is suppressed remarkably by the gas cavity with the increase of the gas ventilation.
文摘A series of projectile and water-tunnel experiments were conducted to investigate the shape characters of natural and ventilated supercavitation. It was found that the shape and dimensions of both the natural supercavitation and the ventilated supercavitation are similar through the comparison of them when the cavitation number is small and equal, and the contour of both the natural supercavitation and the ventilated supercavitation can be calculated effectively with the Savchenko formula. The gravity effect can induce the asymmetry of ventilated supercavitation, and the asymmetry is more apparent as the Froude number is smaller. The empirical formula for calculating the axial deformation of ventilated supercavitation was corrected and expanded based on experiment data. The evolution rules of both the natural supercavitation and the ventilated supercavitation were described, and the vortex frequency of natural cavitation was obtained. In addition, the hysteretic aspect was observed between the development and the fall process of ventilated cavitation.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11002089, 10832007)the Shanghai Leading Academic Discipline Project (Grant No.B206)
文摘When a body navigates with cavity in shallow water, both flexible free surface and rigid bottom wall will produce great influences on the cavity shape and hydrodynamic performances, and further affect the motion attitude and stability of the body. In the present work, characteristics of the natural cavitating flow around a 2-D symmetrical wedge in shallow water were investigated and the influences of two type boundaries on the flow pattern were analyzed. The Volume Of Fluid （VOF） multiphase flow method which is suitable for free surface problems was utilized, coupled with a natural cavitation model to deal with the mass-transfer process between liquid and vapor phases. Within the range of the cavitation number for computation （0.07-1.81）, the cavity configurations would be divided into three types, viz., stable type, transition type and wake-vortex type. In this article, the shapes of the free surface and the cavity surface, and the hydrodynamic performance of the wedge were discussed under the conditions of relatively small cavitation number （〈0.256）. The present numerical cavity lengths generally accord with experimental data. When the cavitation number was decreased, the cavity was found to become longer and thicker, and the scope of the deformation of the free surface also gradually extends. The free surface and the upper cavity surface correspond fairly to their shapes. However, the lower side of the cavity surface was rather leveled due to the influence of wall boundary. The lift and drag coefficients of this 2-D wedge basically keep linear relations with the natural cavitation number smaller than 0.157, whereas direct proportion for drag and inverse proportion for lift.
基金the National Natural Science Foundation of China (No.10832007)the Shanghai Leading Academic Discipline Project (No.B206)
文摘The present simulation investigates the multiphase cavitating flow around an underwater projectile.Based on the homogeneous equilibrium flow assumption,a mixture model is applied to simulate the multiphase cavitating flow including ventilated cavitation caused by air injection as well as natural cavitation.The transport equation cavitating model and a local linear low-Reynolds-number turbulence model are incorporated to the equation system.The calculations are executed based on a suite of computational fluid dynamics code.The hydrodynamics characteristics of flow field under the interaction of natural cavitation and ventilated cavitation are analyzed.The results indicate that the ventilated cavitation numbers and the drag coefficient are relative to the natural cavitation numbers and gas flow rate in the multiphase cavitating flows.
基金supported by the National Natural Science Foundation of China(Grant No:10832007)Shanghai Leading Academic Discipline Project(Project No. B206)
文摘The present simulation investigates the multiphase cavitating flow around an underwater projectile.Based on the Homogeneous Equilibrium Flow assumption,a mixture model is applied to simulate the multiphase cavitating flow including ventilated cavitation caused by air injection as well as natural cavitation that forms in a region where the pressure of liquid falls below its vapor pressure. The transport equation cavitating model is applied.The calculations are executed based on a suite of CFD code.The hydrodynamics characteristics of flow field under the interaction of natural cavitation and ventilated cavitation is analyzed.The results indicate that the ventilated cavitation number is under a combined effect of the natural cavitation number and gas flow rate in the multiphase cavitating flows.
