Study On Thermal Effect And Flow Characteristic Of Cavitating Flow Around Hydrofoil In Thermo-sensitive Fluid

Cavitation in hydraulic machinery often leads to loss of performance and possible physical damage.When the turbopumps of spacecraft and cryopumps in petrochemical industry pump cryogenic fluid at high speed,cavitation often occurs at the inlets of the flow-through components such as impellers and inducers.Unlike water at room temperature,thermal effect is non-negligible in thermo-sensitive fluids cavitating flows,which results in a large difference between the predicted results and the experimental data.It is the fact that liquid-vapor density ratio near the critical temperature point is orders of magnitude less than typical experimental temperature for thermo-sensitive fluids,and the traditional numerical calculation methods and cavitation models do not apply.Therefore,it is of great physical and engineering significance to develop a numerical method for numerically simulating the thermo-sensitive cavitating flows and launching further investigation.In present thesis,thermal effects and flow characteristics of the thermo-sensitive cavitating flow are studied and the main studying contents are as following:Based on the transport equation numerical framework,the conventional Zwart's cavitation model is deduced in detail and an extended transport-based cavitation model with thermal effects is developed.In addition,since the standard RANS method overpredicts the turbulent viscosity in cavitating flow,the filter-based density corrected model is applied to modify turbulent viscosity.Based on the schematic diagram of the thermal boundary layer of a single spherical bubble model,the thermodynamic parameter(50)is derived in detail,and the thermal sensitivity of different fluids is also analyzed.The energy equation is coupled to consider the influence of latent heat of vaporization,an effective computational strategy for thermo-sensitive cavitating flow is established,and the steady flow of liquid nitrogen around the hydrofoil is numerically simulated.The numerical simulation results are compared with the experimental data to verify the validity of the modified cavitation model,and the suppression effect of thermal effect on cavitation at different inflow temperatures is analyzed.The transient thermo-sensitive cavitating flow around a NACA 0015 hydrofoil in fluoroketone is investigated.The numerical results show that the time evolution of the vapour total volume is quasi-periodic and the predicted thermo-sensitive cavitation dynamics behaviour is analysed in detail.The thermal effect of cavitation is studied by the B factor theory to predict the temperature drop.It shows that B-factor theory can predict temperature drop in most regions effectively,but it overpredicts the temperature drops in the sheet cavitation region near the leading edge and cannot predict local temperature increase due to liquefaction exothermic during cavitation collapse.Boundary vorticity flow and skin friction are applied to identify three-dimensional flow separation of hydrofoil suction surface.The coherent relationship among the re-entrant jet,vortex structure and flow separation is analysed in detail.It shows that when the re-entrant jet interacts with the main stream,it causes the formation and shedding of vortex.The formation of vortex structure affects the flow field in turn and often accompanies by the appearance of flow separation.In addition,the blocking effect of the shedding cavitation on the main stream also causes the appearance of separation flow.