Lift-drag characteristics of S-shaped hydrofoil under different cloud cavitation conditions

The purpose of this paper is to study the correlation between the lift-drag variation of the S-shaped hydrofoil and the movement of cloud cavitation. High-speed photography and six-dimensional force-torque balance can well count the frequency of cloud cavitation shedding and the frequency of lift-drag. The cloud cavitation motion characteristics and lift-drag fluctuations of the S-shaped hydrofoil reproduced by numerical simulation are in good agreement with the experimental results. Based on the results of numerical simulation, a judgment index for studying the fluctuation of lift-drag is put forward—pressure intensity coefficient. The pressure intensity coefficient can well quantify the influence of the two important stages of cloud cavitation (shedding and dissipation) in the entire cloud cavitation cycle. The research results of this paper prove the relationship between the motion frequency of cloud cavitation and the main frequency of the lift-drag of the S-shaped hydrofoil, which can provide a reference for the unsteady characteristics of the bi-directional hydraulic machinery under cavitation conditions.