Unsteady Flow Characteristics Analysis And Cavitation Prediction Of 3D Hydrofoil

Cavitation often occurs in the low pressure area such as the edge of the blade of water pump,water turbine and other hydraulic machinery,and the instability of cavitation flow often affects the hydraulic performance of hydraulic machinery.In order to further explore the hydrodynamic characteristics and cavitation flow mechanism of hydraulic machinery,numerical simulation and multiple regression analysis are used to analyze the three-dimensional NACA6408 hydrofoilFluent software was used to simulate the cavitation under the conditions of incoming velocity of 1,5,10,15 and 20m/s,incoming attack angle of 4°and 8°respectively.The influence of flow rate,pressure,turbulent kinetic energy,maximum/minimum velocity and maximum/minimum pressure on cavitation development and the exploration of cavitation inducement were analyzed.The results show that:the void volume fraction at the middle section of the wingspan(l/2=75mm)increases gradually with the incoming flow velocity;the cavitation generated by cavitation transits from the floating type to the attached type,and goes through the stages of initiation,growth,development and collapse with time,which has strong unsteady flow characteristics.There is no cavitation in the high pressure region of the suction surface,but the flow rate,pressure,turbulent kinetic energy and X/Y/Z velocity in the low pressure region change significantly,which is an important factor to induce cavitation.In addition,airfoil structure is also one of the factors inducing cavitation.There are many factors that induce cavitation.It is one of the directions to explore the influence of various influencing factors on cavitation by statistical methods.In this paper,many influencing factors of cavitation are introduced into the regression model based on SPSS software,and the cavitation volume fraction is taken as the measurement standard.The results showed that the adjusted R~2 of section B4 was 0.978,which was statistically significant.In addition,section B4 is selected as the analysis object,and the influencing factors of cavitation in section B4 are introduced into the regression model.The adjusted R~2 is 0.656,and then the regression equation is established.Cross section,cross-section area and inlet velocity are important factors to induce cavitation.The critical velocity of cavitation is predicted by cross-section,cross-section area and inlet velocity,which shows that multiple regression analysis has certain guiding significance to predict the critical velocity of cavitation.