• 한국전산유체공학회:학술대회논문집
• /
• 2008.03b
• /
• pp.420-423
• /
• 2008

This present work is to find optimum design of a NACA65 axial fan blade with weighted average surrogate model. The numerical analysis by Reynolds-average Navier-Stokes equations with shear stress turbulence(SST) is discretized by finite volume approximations and solved on hexahedral grids for flow analysis. The blade aerodynamic shape is modified by six design variables for the optimization. The blade profile as well as stacking line is modified to enhance blade total efficiency. Six design variables, airfoil maximum camber, maximum camber location, leading edge radius, trailing edge radius, lean angle at 50% span and lean angle at 100% span, are selected for blade profile to enhance the total efficiency. The PBA model which is basically weighted average of the basis surrogates is used to find the optimal design in the design space from the constructed response surface model for the objective function. By the optimization, the total efficiency is increased by 1.4%.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.32 no.8
• /
• pp.20-28
• /
• 2004

For the prediction on the onset of oblique shock wave-induced vortex breakdown, computational studies on the Oblique Shock wave/Vortex Interaction (OSVI) are conducted and compared with both experimental results and analytic mode1. A Shock-stable numerical scheme, the Roe scheme with Mach number-based function (RoeM), and a two-equation eddy viscosity-transport approach arc used for three-dimensional turbulent flow computations. The computational configuration is identical to available experiment, and we attempt to ascertain the effect of parameters such as a vortex strength, streamwise velocity deficit, and shock strength at a freestream Mach number of 2.49. Numerical simulations using the k-w SST turbulence model and suitably modeled vortex profiles are able to accurately reproduce many fine features through a direct comparison with experimental observations. The present computational approach to determine the criterion on the onset of oblique shock wave-induced vortex breakdown is found to be in good agreement with both the experimental result and the analytic prediction.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.41 no.7
• /
• pp.516-523
• /
• 2013

The tip clearance effect on counter-rotating ducted fan of VTOL UAV in hovering condition, was investigate using computational analysis. The $k-{\omega}$ SST turbulence model is employed in this study. The numerical results of baseline model are validated by wind tunnel test in hovering and forward conditions. It is observed that if tip clearance of one rotor in the counter-rotating ducted fan increase then the thrust coefficient of another rotor increases. In Addition to this, when the tip clearance of the rear rotor increases, the thrust of the ducted fan is improved due to increasing of average total pressure at exit plane.

• Transactions of the Korean hydrogen and new energy society
• /
• v.26 no.4
• /
• pp.386-392
• /
• 2015

Flow characteristics inside a 10 inch ball valve have been analyzed using three-dimensional numerical analysis and experiments. Continuity and three-dimensional Reynolds-averaged Navier-Stokes equations have been used as governing equations for the numerical analysis. The numerical model has been constructed through the grid dependency test and validation with the results of experiments to ensure reliability and numerical effectiveness. The shear stress transport (SST) model has been used as the turbulence closure. The experimental test-rig has been constructed to measure pressure, temperature and flow rate along the pipeline. Some valve opening angles have been tested to evaluate the flow characteristics inside the ball valve and pipeline. The results show that the rapid pressure variations is observed while the valve opening angle decreases, which caused by flow separation at the downstream of the ball valve.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.10 no.2
• /
• pp.212-224
• /
• 2018

The characteristics of the relationship between the evolution of propeller trailing vortex wake and skew angle are numerically examined based on four different five-blade David Taylor Model Basin (DTMB) model propellers with different skew angles. Numerical simulations are based on Reynolds-averaged Naviere-Stokes (RANS) equations combined with SST $k-{\omega}$ turbulence model. Results show that the contraction of propeller trailing vortex wake can be restrained by increasing skew angle and loading conditions, and root vortices fade away when the propeller skew angle increases. With the increase of the propeller's skew angle, the deformation of the hub vortex and destabilization of the tip vortices are weakening gradually because the blade-to-blade interaction becomes weaker. The transition trailing vortex wake from stability to instability is restrained when the skew increases. Furthermore, analyses of tip vortice trajectories show that the increasing skew can reduce the difference in trailing vortex wake contraction under different loading conditions.

• International Journal of Fluid Machinery and Systems
• /
• v.8 no.3
• /
• pp.142-154
• /
• 2015

Nowadays, computational fluid dynamics is commonly used by design engineers to evaluate and compare losses in hydraulic components as it is less expensive and less time consuming than model tests. For that purpose, an automatic tool for casing and distributor analysis will be presented in this paper. An in-house mesh generator and a Reynolds Averaged Navier-Stokes equation solver using the standard $k-{\omega}$ shear stress transport (SST) turbulence model will be used to perform all computations. Two solvers based on the C++ OpenFOAM library will be used and compared to a commercial solver. The performance of the new fully coupled block solver developed by the University of Lucerne and Andritz will be compared to the standard 1.6ext segregated simpleFoam solver and to a commercial solver. In this study, relative comparisons of different geometries of casing and distributor will be performed. The present study is thus aimed at validating the block solver and the tool chain and providing design engineers with a faster and more reliable analysis tool that can be integrated into their design process.

• Journal of the Korean Society of Visualization
• /
• v.14 no.3
• /
• pp.32-37
• /
• 2016

In this study, the mixing process of two distinct flow is numerically investigated. Two flow with different physical properties (resin and hardener) are mixed through the opposing mixing jets. At a high pressure mixing process, the high speed flow is provided by two in-line nozzles. In the case of numerical modeling, Reynolds-Averaged Navier-Stokes Equations (RANS) is conducted to model the flow pattern inside the chamber. Additionally, SST k-omega turbulence model is selected to predict the kinetic energy of flow in impingement zone. The results show that mixing of two distinct flows would be efficient if the velocity of jet is high enough and nozzle diameter is a predominant parameter. Also, this velocity would create higher shear stress between two distinct flows which increases the mixing quality as well as strength of formed vortices. Eventually, the histogram of concentration fraction of resin is examined in order to show the quality of mixing and the range of concentration fractions in the output of chamber.

• 한국신재생에너지학회:학술대회논문집
• /
• 2009.06a
• /
• pp.516-520
• /
• 2009

This study describes aerodynamic characteristics for the HAWT (Horizontal Axis Wind Turbine) rotor blade using general CFD(Computational Fluid Dynamics) code. The boundary conditions for analysis are validated with the experimental result by the NREL (National Renewable Energy Laboratory)/NASA Ames wind tunnel test for S809 airfoil. In the case of wind turbine rotor blade, complex phenomena are appeared such as flow separation and re-attachment. Those are handled by using a commercial flow analysis tool. The 2-equation k-$\omega$ SST turbulence model and transition model appear to be well suited for the prediction. The 3-dimensional phenomena in the HAWT rotor blade is simulated by a commercial 3-D aerodynamic analysis tool. Tip vortex geometry and Radial direction flows along the blade are checked by the analysis.

• 한국전산유체공학회:학술대회논문집
• /
• 2010.05a
• /
• pp.389-396
• /
• 2010

In this paper, a new computational code was developed using Chorin's artificial compressibility method to solve the two-dimensional incompressible Navier-Stokes equations. In spatial derivatives, Roe's flux difference splitting was used for the inviscid flux, while central differencing was used for the viscous flux. Furthermore, AF-ADI with dual time stepping method was implemented for accurate unsteady computations. Two-equation turbulence models, Menter's $k-{\omega}$ SST model and Coakley's $q-{\omega}$ model, hae been adopted to solve high-Reynolds number flows. A number of numerical simulations were carried out for steady laminar and turbulent flow problems as well as unsteady flow problem. The code was verified and validated by comparing the results with other computational results and experimental results. The results of numerical simulations showed that the present developed code with the artificial compressibility method can be applied to slve steady and unsteady incompressible flows.

• Journal of the Society of Naval Architects of Korea
• /
• v.53 no.4
• /
• pp.266-274
• /
• 2016

Many researchers have been trying to improve the propulsion efficiency of a propeller. In this study, the numerical analysis is carried out for the POW(Propeller Open Water test) performance of a propeller equipped with an energy saving device called PHVC(Propeller Hub Vortex Control). PHVC is aimed to control the propeller hub vortex behind the propeller so that the rotational kinetic energy loss can be reduced. The unsteady Reynolds Averaged Navier-Stokes(URANS) equations are assumed as the governing flow equations and are solved by using a commercial CFD(Computational Fluid Dynamics) software, where SST k-ω model is selected for turbulence closure. The computed characteristic values, thrust, torque and propulsion efficiency coefficients for the target propeller with and without PHVC and the local flows in the propeller wake region are validated by the model test results of KRISO LCT(Large Cavitation Tunnel). It is concluded from the present numerical results that CFD can be a good promising method in the assessment of the hydrodynamic performance of PHVC in the design stage.