NUMERICAL STUDY OF MULTISCALE CAVITATING FLOW AROUND A HYDROFOIL

The multiscale effect of cavitation is a complex hydrodynamic phenomenon involving macroscale cavitation, microscale cavitation bubbles and transformation between scales. The cavitating flow around a NACA66 hydrofoil is simulated based on the established Euler-Lagrange algorithm. The macroscale cavitation vapor was captured through a large eddy simulation (LES) method and the volume of fluid (VOF) method in an Eulerian analysis. The motion, growth and collapse of sub-grid scale discrete bubbles were solved through discrete bubble model (DBM) in Lagrangian frame. Meanwhile, the solution model of different scale cavitation is selected through the comparison of scale between cavitation cavity and the local grid. The experimental results are compared with the numerical results to verify the accuracy of the numerical method. The results show that the number of discrete bubbles is closely related to the development of cloud cavitation. The number of discrete bubbles fluctuate little in the growth stage of attached sheet cavity with the bubbles mainly distributed at the interface of water and vapour. With the re-entrant jet occur at the trailing edge of attached cavity and develop to leading edgy of hydrofoil, the bubble number gradually increase and fill up the jet disturbance region. When the cavity detach, converge and shed downstream along with the hydrofoil, the discrete bubble number increase rapidly and the bubbles dispersed in the mixing region of water and vapour. Moreover, the probability density function of discrete bubble diameter conforms to Gamma distribution for the whole stage of cloud cavitation. With the increase of cavitation diameter, the number of cavitation first increases and then decreases. Additionally, the characteristics of the cavitation turbulent flow field have an important influence on the distribution of bubbles, and the discrete bubble is mainly distributed in the region of strong turbulence intensity, vortex and re-entrant flow.