Journal of Shipping and Ocean Engineering 2 (2012) 10-17 Numerical Study of Unsteady Behavior of Partial Cavitation on Two Dimensional Hydrofoils Md. Nur-E-Mostafa 1 , Md. Mashud Karim 2 and Md. Manirul Alam Sarker 3 1. Department of Environment and System Sciences, Graduate School of Environment and Information Science, Yokohama National University, Yokohama 240-8501, Japan 2. Department of Naval Architecture and Marine Engineering, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh 3. Department of Mathematics, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh Abstract: This paper deals with time dependent performance characteristics of cavitating hydrofoils, the flow around which has been simulated using pressure-based finite volume method. A bubble dynamics cavitation model was used to investigate the unsteady behavior of cavitating flow and describe the generation and evaporation of vapor phase. For choosing the turbulence model and mesh size a non cavitating study was conducted. Three turbulence models such as Spalart-Allmaras, Shear Stress Turbulence (SST) k-ω model, Re-Normalization Group (RNG) k-ε model with enhanced wall treatment are used to capture the turbulent boundary layer along the hydrofoil surface. The cavitating study presents an unsteady behavior of the partial cavity attached to the foil at different time steps for σ = 0.8 and σ = 0.4. Moreover, this study is focused on cavitation inception, the shape and general behavior of sheet cavitation, lift and drag forces for different cavitation numbers. Key words: Cavitation, CAV2003 hydrofoil, finite volume method, turbulence model, unsteady flow. 1. Introduction Cavitation in hydraulic machines causes different problems like vibration, increase in hydrodynamic drag, pressure pulsation, and change in flow kinematics, noise and erosion of solid surface. Most of these problems are related to transient behavior of cavitation structure. Cavitation erosion is strongly related to unsteady fluctuations of the cavitation zone. So, cavitation can be defined as the breakdown of the liquid medium under very low pressure [1]. Hence, a study of unsteady cavitating behavior is essential for a good prediction of the problem. Partial cavitation is commonly encountered on lifting surface such as hydrofoils, propeller blades, pumps, etc.. To investigate cavitation phenomena and validate numerical procedures, a number of investigations were Corresponding author: Md. Mashud Karim, professor, research fields: computational ship geometry, hydrodynamics, resistance & propulsion, hydrofoil and propeller optimization. E-mail: mmkarim@name.buet.ac.bd. performed in the past [2-6]. In the last decade various methods for numerical simulation of cavitating flow were developed. Most of the studies treat the two phase flow as a single vapor-liquid phase mixture flow. The evaporation and condensation can be modeled with different source terms which are usually derived from the Rayleigh-Plesset bubble dynamics equation. Recently different authors proposed to consider a transport equation model for the void ratio, with vaporization/condensation source terms to control the mass transfer between two phases [7]. This method has the advantage that it can take into account the time influence on the mass transfer phenomena through empirical laws for the source term. It also avoids using quantities like bubble number density and initial bubble diameter. A cavitation model, based on bubble dynamics equation, is used for computation of cavitating flows. Bubbles may appear in regions of low pressure. The bubbles are carried along by the DAVID PUBLISHING D