Numerical Simulation Of Ultrasonic Cavitation Based On FLUENT

For a long time, cavitation erosion has significantly affected the capability and service life of machines, such as valve, water pump, fluid assembly of hydraulic turbine and marine propeller. Cavitation erosion leads to decline of efficiency, and even endangers the working order of machines, which results in remarkable losing of energy and material. Simulation calculation of fluid flow in ultrasonic cavitation is performed by FLUENT in this paper. Through observing variation of absolute pressure, vapor volume fraction and velocity magnitude in flow field, mechanism of ultrasonic cavitation and influence factors are investigated. Primary conclusions are as follows:(1) While sample vibrates, middle area on the sample is the primary cavitation area because of great variation of pressure and vapor volume fraction. Pressure on the marginal area of sample is always higher than vaporization pressure of water during fluid flows. So cavitation hardly ever occurs because of low vapor volume fraction. At the same time, passing water has an effect on the marginal area, and wear abrasion could happen to the marginal area of sample. On the sub-marginal area of sample, vapor bubbles collapse when flowing rapidly. Therefor, the sample surface appears radialized scratch.(2) Compared with testing program of vibrational sample, variation of velocity magnitude is bigger and pressure is higher on the marginal area of sample in the testing program of fixed sample. So it has an stronger damage effect and a more evident appearance of wear abrasion. Variation of pressure on the middle of sample is larger, and vapor volume fraction instantaneous declines greatly. Therefor, this testing program has strongger cavitation erosion effect on the middle area of sample.(3) The under-relaxation factors of density and body force affect simulation results intensively. RNG k-εmodel is sensitivity to low pressure. Non-equilibrium wall function and enhanced wall function are more sensitivite to variation of near-wall pressure. The higher temperature of water is, the higher vaporization pressure is, while variation of pressure in flow field is smaller, and pressure changes more steadily, but variation of vapor volume fraction on sample is bigger. The bigger non-condensable gas mass fraction is, the smaller variation of pressure on sample is. Synchronously, vapor volume fraction on sample is higher.