Numerical investigation of unsteady cavitation around a twisted hydrofoil

Abstract

In this paper, the unsteady cavitating flow around a symmetrical twisted hydrofoil is investigated numerically. Cavitating flow characteristics are analyzed in terms of dynamical behaviors and temporal/spatial fluctuations of the cavities along the hydrofoil. At the midsection of the foil, sheet cavity firstly grows with nearly constant speed until the occurrence of the reverse flow at the closure line. During the reverse phase the flow moves upstream, and the sheet cavity keeps growing turbulently with low vapor content at the closure area. Fast Fourier Transform (FFT), Bispecturm and Dynamic Mode Decomposition (DMD) analyses show the existence of harmonics of the shedding frequency, of which the double and triple frequency are captured but only the fundamental frequency dominates the cavitating field. Pressure fluctuations around the hydrofoil and force coefficients are governed by the acceleration of vapor cavity. Application of Proper Orthogonal Decomposition (POD) displays the large-scale coherent structures among cavity shedding evolution. The sheet cavity growth, the main cavity shrinking and developing into a pair of root-like cavity structure and the sector cavity structure are captured by the first mode.