Numerical Analysis And Experimental Research On Cavitation Suppression By Active Jet Flow

The damages of uncontrollable cavitation are widespread and serious.Cavitation often brings some serious negative effects in hydraulic machinery,such as vibration,noise,performance degradation,equipment corrosion,etc.Therefore,the research of cavitation suppression is of great significance.In this paper,experiments of active jet flow to suppress cavitation around NACA66(MOD)hydrofoil are carried out,and the mechanism of active jet flow to suppress cavitation is revealed combined with CFD numerical simulation.The main conclusions of this paper are as follows:The effects of active jet flow on sheet cavitation and cloud cavitation were studied experimentally.The cavitation flow field was observed by a high-speed visualization system.The results show that the jet can effectively weaken the cavitation.For sheet cavitation,the jet can significantly suppress the time-averaged dimensionless cavitation area,but the jet has little effect on the oscillation frequency of sheet cavitation.For cloud cavitation,active jet can effectively weaken the intensity of cavitation and decrease the time-averaged dimensionless cavitation area of,the frequency of cavitation shedding can also be reduced,but there is still a phenomenon of cavitation shedding at the trailing edge of hydrofoil.Cavitation is a severe turbulent flow phenomenon.Based on the experimental results,comparing the filter-based density corrected model(FBDCM)with other turbulence models widely used recent years,it is confirmed that the FBDCM turbulence model combined with ZGB cavitation model can accurately capture the details of cavitation shedding,the cavitation regime and the shedding frequency is in good agreement with the experimental results.After that,the mechanism of cloud cavitation suppression has been studied.The results show that the jet changes the pressure and velocity distribution of suction surface,and the pressure value in the low pressure zone is increased,the pressure gradient of trailing edge is decreased.So that the pressure fluctuation decreases and the velocity boundary layer thins which increase the ability to resist the adverse pressure gradient.In the process of vorticity transport,the vortex shedding phenomenon is weakened by the decrease of the vortex stretching term and vortex dilatation term,and the vapor-liquid interface is reduced by the decrease of the baroclinic torque term.Through one-dimensional analysis of cavitation stability,the results show that the pressure fluctuation around the cavitating hydrofoil is proportional to the second derivative of cavity volumethe pressure fluctuation and is proportional to the first derivative of flow rate difference.And the essence of jet cavitation suppression is that the pressure in low pressure zone is improved,the intrinsic frequency of cavitation is changed and phase transition rate are reduced by the active jet,so the cavity volume is reduced and then the cavitation is suppressed.