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SENSITIVITY EVALUATION OF EMPIRICAL COEFFICIENTS IN THE CAVITATION MODELS
Cong-Tu Ha,Wam-Gyu Park 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.11
Cavitating flow is notoriously complex because of the issues of large density jump across the irregularly shaped phase boundary, interaction between phase change, turbulence, and the stiffness in the numerical solution. These issues can be modeled with the aid of the multiphase transport equations with appropriate source terms to regulate the mass transfer between phases. In this paper, a sensitivity analysis of empirical coefficients to access the predictive capability of the existing cavitation models is presented. Three cavitation models are considered. Two empirical coefficients used in each cavitation model are accessed, namely Cdest, and Cprod, that directly affect the evaporation and condensation of phases. The coefficients are non-dimensionalized with the freestream values to have correct dimensional form as the convective terms. The present compressible multiphase Reynolds averaged Navier-Stokes solver employs a preconditioning algorithm. The standard k-ε turbulence model with wall functions is employed as the turbulence closure. The governing equations are solved on multi-block structured curvilinear grids. The sensitivity of the computations for turbulent cavitating flows over the axisymmetric bodies to the empirical coefficients are performed. The empirical coefficients in three cavitation models have been successfully calibrated with the experimental data for different flow conditions. The sensitivity analysis indicates that the cavitation flow characteristic as well as the stability of the numerical method be quite sensitive to the model coefficients. To confirm the use of the calibrated model coefficients, the computations of cavitating flow over the Clark-Y hydrofoil is then carried out. The multiphase solver provides overall satisfactory results for the prediction of cavitating flow behavior.
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NUMERICAL SIMULATION OF VERTICAL WATER-EXIT AND WATER-ENTRY OF CAVITATING PROJECTILES
Van-Tu Nguyen,Cong-Tu Ha,Wam-Gyu Park 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.11
The present study focuses on the simulation of unsteady ventilated-cavitating flow during the vertical water-exit and water-entry of projectiles with and without exhaust plume. The propulsion exhaust plume gas embedded within the surrounding liquid strongly affects on the wake of flow. For simulation of water-exit and water-entry behavior of the cavitating projectiles which presents aspects of the flow physics such as cavity shape and phase topography of the flow during the processes, a numerical multi-phase homogeneous mixture model is utilized. The model is developed based on the unsteady incompressible Reynolds-averaged Navier-Stokes equations. Preconditioning pseudo-time stepping method is employed to improve the computational efficiency of the model. The results indicate that characteristics of cavity flow induced during water-exit and water-entry primarily depend on the geometry of projectiles and the velocities of flow. In addition, the gas exhaust delays the surface closure of the water-entry cavity that is one of the most important events in later cavity growth.
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Van-Tu Nguyen,Cong-Tu Ha,Wam-Gyu Part 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.5
A numerical multi-phase homogeneous mixture model for simulating the natural- and ventilated-cavitating flows around underwater bodies is presented. The model is formulated by using incompressible Reynolds-averaged Navier-Stokes equations, consisting of the mixture volume, liquid and non-condensable gas volume fraction and mixture momentum equations. A preconditioned, dual-time algorithm is applied to accommodate the unsteady physics of natural- and ventilated-cavitating flow. To demonstrate the computational capacities of this model, cavitating flows around underwater body are calculated under several selected conditions and the results well agree with available experimental data and other published results. Solutions for the natural- and ventilated-cavitating flows around an underwater vehicle are presented. The study concludes that the gas ventilation into the flow near the vehicle induces the larger ventilated cavity and strongly impacts on cavity and development of the flow.
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전치 가이드베인을 가지는 수중 덕트 프로펠러 주위의 전산 유동 해석
유혜란(Hye-Ran Yu),정영래(Young-Rae Jung),박원규(Wam-Gyu Park) 한국전산유체공학회 2004 한국전산유체공학회지 Vol.9 No.2
The present work solved 3D incompressible RANS equations on a rotating, multi-blocked grid system to efficiently analyze ducted marine propulsor with the interaction of propeller guidevane and annular duct. To handle the interface boundary between the guidevane and the propeller, a sliding multiblock technique based on the cubic spline interpolation was applied. To validate the present code, a turbine flow was simulated and the time-averaged pressure coefficients were compared with experiment. After the code validation, the flowfield around a ducted marine propeller with pre-swirl guidevane was simulated.
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