Numerical investigation of cloud cavitation and cavitation noise on a hydrofoil section

Partial cavitating flow and cloud cavitation on a hydrofoil section are numerically investigated. A fully compressible, density based homogeneous equilibrium model is employed along with a RANS turbulence model and high-order numerical methods based on a sixth-order central compact scheme and localized artificial diffusivity scheme are used to resolve the cavitating flow and pressure waves generated by cloud cavitation. Predicted results compare well with the experimental measurments for steady/unsteady partial cavitating flows on a NACA66 hydrofoil at cavitation number, σ=1.0-1.4 and angle of attack 6 and 8 degree. Detailed experimental data from the work of Leroux et al. were provided by Prof. J.-A. Astolfi at Institut de Recherche de l’Ecole Navale, France. Numerical visualizations of cloud cavity evolution and surface pressure signals show relatively good agreement with the experimental data. The re-entrant jet flow and pressure wave generated by collapse of cloud cavity are closely investigated. The mechanism associated with two different unsteady dynamics of cloud cavitation observed in previous numerical/experimental study for angle of attack 6 and 8 degree are further explored using the present computational results. The pressure pulse generated by the collapse of bubble cloud and the flow-blockage effect caused by a large cavity cloud are found to be responsible for the shifting of cloud cavitation dynamics. INTRODUCTION Severe cavitation noise and erosion damage are caused by cloud cavitation. Formation and collapse of such clouds of cavitation bubbles generate strong pressure waves which are responsible for the noise and erosion. There are several experimental studies for cloud cavitation especially on hydrofoil sections [1–7]. In these experiments, it is observed that the partial sheet cavity is periodically broken-up and rolls up into bubble clouds. The re-entrant jet that flows under the cavity has been believed to be the origin of such cavity destabilization. Pressure wave phenomena is another important feature of cloud cavitation. Reisman et al. [4] investigated the collapse of well-defined and separate cavity clouds for a pitching hydrofoil. Several types of propagating structures (shock waves) which formed in a collapsing cloud were observed by correlating surface pressure measurement with high-speed motion images. Leroux et al. [5,6] studied partial sheet /cloud cavitation on a stationary hydrofoil. Based on the analysis of surface pressure measurements, they indicated that the pressure wave generated by shedding of cloud cavitation effects the dynamics of cloud cavitation itself. Additionally, the shifting of cloud cavitation dynamics reported in several experiments [3, 6] is also very interesting. However, it is very difficult to measure the re-entrant jet flow inside the cavity and pressure wave phenomena in detail. In this respect, numerical simulation is considered an important tool for close investigation of the flow physics. The objective of present study is the numerical investigation of cloud cavitation and cavitation noise (pressure wave gener-