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Journal of computational fluids engineering
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Journal DOI :
Korea Society of Computational Fluids Engineering
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Volume & Issues
Volume 17, Issue 4 - Dec 2012
Volume 17, Issue 3 - Sep 2012
Volume 17, Issue 2 - Jun 2012
Volume 17, Issue 1 - Mar 2012
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HEAT-TRANSFER ANALYSIS OF A COOLING CHANNEL WITH INCLINED ELLIPTICAL DIMPLES
Kim, H.M. ; Moon, M.A. ; Kim, K.Y. ;
Journal of computational fluids engineering, volume 17, issue 1, 2012, Pages 1~7
DOI : 10.6112/kscfe.2012.17.1.001
This paper deals with a parametric study on inclined elliptical dimples to enhance heat transfer in a channel. Three-dimensional Reynolds-averaged Naiver-Stokes equations are solved to estimate flow and heat transfer in dimpled channel. As turbulence closure, the low-Re shear stress transport model is employed. Two non-dimensional geometric variables, dimple ellipse diameter ratio and angle of main diameter to flow direction are selected for the parametric study. The inclined elliptical dimples show higher heat-transfer performance but with higher pressure drop compared to the circular dimples. And there is an optimum inclination angle that gives the maximum heat transfer.
NUMERICAL SIMULATION OF THREE-DIMENSIONAL INTERNAL WAVES USING THE FDS SCHEME ON THE HCIB METHOD
Shin, Sang-Mook ;
Journal of computational fluids engineering, volume 17, issue 1, 2012, Pages 8~15
DOI : 10.6112/kscfe.2012.17.1.008
A code developed using the flux-difference splitting scheme on the hybrid Cartesian/immersed boundary method is applied to simulate three-dimensional internal waves. The material interface is regarded as a moving contact discontinuity and is captured on the basis of mass conservation without any additional treatment across the interface. Inviscid fluxes are estimated using the flux-difference splitting scheme for incompressible fluids of different density. The hybrid Cartesian/immersed boundary method is used to enforce the boundary condition for a moving three-dimensional body. Immersed boundary nodes are identified within an instantaneous fluid domain on the basis of edges crossing a boundary. The dependent variables are reconstructed at the immersed boundary nodes along local normal lines to provide the boundary condition for a discretized flow problem. The internal waves are simulated, which are generated by an pitching ellipsoid near an material interface. The effects of density ratio and location of the ellipsoid on internal waves are compared.
DEVELOPMENT OF UNEVEN FAN BY AERO-ACOUSTICS ANALYSIS & OPTIMIZATION METHOD
Kim, J.S. ; Kim, H.S. ; Hyun, K.T. ;
Journal of computational fluids engineering, volume 17, issue 1, 2012, Pages 16~22
DOI : 10.6112/kscfe.2012.17.1.016
Acoustic pressure field around the centrifugal fan is predicted by a aero-acoustic splitting method. Unsteady flow field is obtained by solving the incompressible Navier-Stokes equations using commercial code, while the acoustic waves generated inside the centrifugal fan and shroud are predicted by solving the far field acoustics analysis. Computational results show that the acoustic waves of BPF tone are generated by interactions of the blades with the shroud. Acoustic results is validated by experimental results This paper describes the influence of geometric parameters on the noise generation from the section of blades and shroud. One of the effective ways to reduce BPF noise is optimization method using Genetic Algorithm, which effectively minimize eccentricity, is suggested. New improving design was developed by optimization method.
NUMERICAL SIMULATION OF PRESSURE CHANGE INSIDE CABIN OF A TRAIN PASSING THROUGH A TUNNEL
Kwon, H.B. ; Yun, S.H. ; Nam, S.W. ;
Journal of computational fluids engineering, volume 17, issue 1, 2012, Pages 23~28
DOI : 10.6112/kscfe.2012.17.1.023
The pressure transient inside the passenger cabin of high-speed train has been simulated using computational fluid dynamics(CFD) based on the axi-symmetric Navier-Stokes equation. The pressure change inside a train have been calculated using first order difference approximation based on a linear equation between the pressure change ratio inside a train and the pressure difference of inside and outside of the train. The numerical results have been assessed for the KTX train passing through a 9km long tunnel of Wonju-Kangneung line at the speed of 250km/h assuming that the train is satisfying the train specification for airtightness required by the regulation.
FLUID-STRUCTURE INTERACTION ANALYSIS FOR VORTEX-INDUCED VIBRATION OF CIRCULAR CYLINDER
Kim, S.H. ; Ahn, H.T. ; Ryue, J.S. ; Shin, H.K. ; Kwon, O.J. ; Seo, H.S. ;
Journal of computational fluids engineering, volume 17, issue 1, 2012, Pages 29~35
DOI : 10.6112/kscfe.2012.17.1.029
Fluid-Structure Interaction analysis of a circular cylinder surrounded by incompressible turbulent flow is presented. The fluid flow is modeled by incompressible Navier-Stokes equations in conjunction with large-eddy simulation for turbulent vortical flows. The circular cylinder is modeled as elastic continuum described by elasto-dynamic equation of motion. Finite element method based approach is utilized for unified formulation of fluid-structure interaction analysis. The magnitude and frequency of structural response is analysed in comparison to the driving fluid forces.
NUMERICAL STUDY WITH VENT SHAFT POSITION IN UNDERGROUND STATION
Oh, Hyun-Joo ; Shin, Dea-Yong ; Lee, Sang-Gun ; Kim, Dong-Hyun ; Kim, Charn-Jung ;
Journal of computational fluids engineering, volume 17, issue 1, 2012, Pages 36~43
DOI : 10.6112/kscfe.2012.17.1.036
When a high-speed train passes an underground station, large pressure waves are generated due to the piston effect. These pressure waves can cause the problems of vibration and noise as well as the ear discomfort of passengers at the underground station. This work numerically analyzed the pressure wave generation and propagation in an high-speed railway underground station, and the optimal location for vent shafts was studied to improve the passenger comfort by reducing the magnitude of the pressure wave and its rate of change. The evolution of pressure field in the underground station was calculated using a CFD(Computational Fluid Dynamics) software(Fluent), where the axis-symmetric two-dimensional model verified by Wu was used. And this study is applied to modelling of the underground station and the tunnel from Daegok station A-line of GTX(Great Train Express). From the result, we can have a conclusion that the role of vent shafts respectively were different according to the position in and out the underground station. Also Vent shaft in the underground station widely reduced pressure magnitude. And vent shaft out underground station reduced initial pressure peak value. Double vent shafts installed at tunnel toward station entrance and inside of the tunnel are the most efficient to reduce pressure. and pressure reduction increases according to the number of vent shaft.
IMPLEMENTATION OF IMMERSED BOUNDARY METHOD TO INCOMPRESSIBLE NAVIER-STOKES SOLVER USING SIMPLE ALGORITHM
Kim, G.H. ; Park, S.O. ;
Journal of computational fluids engineering, volume 17, issue 1, 2012, Pages 44~53
DOI : 10.6112/kscfe.2012.17.1.044
Immersed boundary method(IBM) is a numerical scheme proposed to simulate flow field around complex objectives using simple Cartesian grid system. In the previous studies, the IBM has mostly been implemented to fractional step method based Navier-Stokes solvers. In this study, we implement the IBM to an incompressible Navier-Stokes solver which uses SIMPLE algorithm. The weight coefficients of the bi-linear and quadratic interpolation equations were formulated by using only geometric information of boundary to reconstruct velocities near IB. Flow around 2D circular cylinder at Re=40 and 100 was solved by using these formulations. It was found that the pressure buildup was not observed even when the bi-linear interpolation was adopted. The use of quadratic interpolation made the predicted aerodynamic forces in good agreement with those of previous studies. For an analysis of moving boundary, we smulated an oscillating circular cylinder with Re=100 and KC(Keulegan-Carpenter) number of 5. The predicted flow fields were compared with experimental data and they also showed good agreements.
VALIDATION OF TRANSITION FLOW PREDICTION AND WIND TUNNEL RESULTS FOR KU109C ROTOR AIRFOIL
Jeon, S.E. ; Sa, J.H. ; Park, S.H. ; Kim, C.J. ; Kang, H.J. ; Kim, S.B. ; Kim, S.H. ;
Journal of computational fluids engineering, volume 17, issue 1, 2012, Pages 54~60
DOI : 10.6112/kscfe.2012.17.1.054
Transition prediction results are validated with experimental data obtained from a transonic wind tunnel for the KU109C airfoil. A Reynolds-Averaged Navier-Stokes code is simultaneously coupled with the transition transport model of Langtry and Menter and applied to the numerical prediction of aerodynamic performance of the KU109C airfoil. Drag coefficients from the experiment are better correlated to the numerical prediction results using a transition transport model rather than the fully turbulent simulation results. Maximum lift coefficient and drag divergence at the zero-lift condition with Mach number are investigated. Through the present validation procedure, the accuracy and usefulness of both the experiment and the numerical prediction are assessed.
SHAPE DESIGN FOR DISC OF A DOUBLE-ECCENTRIC BUTTERFLY VALVE USING THE TOPOLOGY OPTIMIZATION TECHNIQUE
Yang, S.M. ; Baek, S.H. ; Kang, S. ;
Journal of computational fluids engineering, volume 17, issue 1, 2012, Pages 61~69
DOI : 10.6112/kscfe.2012.17.1.061
In this paper, the shape design process is briefly discussed emphasizing the use of topology optimization in the conceptual design stage. The basic idea is to view feasible domains for sensitivity region concepts. In this method, the main process consists of two steps: as the design moves further inside the feasible domain using Taguchi method, and thus becoming more successful topology optimization, the sensitivity region becomes larger. In designing a double-eccentric butterfly valve, related to hydrodynamic performance and disc structure, are discussed where the use of topology optimization has proven to dramatically improve an existing design and significantly decrease the development time of a shape design. CFD analysis results demonstrate the validity of this approach.
UNSTEADY AERODYNAMIC ANALYSIS OF HELICOPTER ROTOR BLADES USING DIAGONAL IMPLICIT HARMONIC BALANCE METHOD
Im, D.K. ; Choi, S.I. ; Kim, E. ; Kwon, J.H. ; Park, S.H. ;
Journal of computational fluids engineering, volume 17, issue 1, 2012, Pages 70~77
DOI : 10.6112/kscfe.2012.17.1.070
In this paper, diagonal implicit harmonic balance method with overset grid technique is applied to analyze helicopter rotor blade flow in hover and forward flight condition. The chimera grid need interpolation time with sub-grid and background grid in moving problem such as forward flight on every time step. Present method is available enough to reduce the grid module interpolation time. In order to demonstrate present method, Caradonna & Tung's and AH-1G rotor blades are used and the results are compared to other researchers' result and experimental data.
COMPARISON OF CFD SIMULATION AND EXPERIMENT OF CAVITATING FLOW PAST AXISYMMETRIC CYLINDER
Park, H.M. ; Park, W.G. ; Jung, C.M. ;
Journal of computational fluids engineering, volume 17, issue 1, 2012, Pages 78~85
DOI : 10.6112/kscfe.2012.17.1.078
Cavitation causes a great deal of noise, damage to components, vibrations, and a loss of efficiency in devices, such as propellers, pump impellers, nozzles, injectors, torpedoes, etc., Thus, cavitating flow simulation is of practical importance for many engineering systems. In this study, a two-phase flow solver based on the homogeneous mixture model has been developed. The flow characteristics around an axisymmetric cylinder were calculated and then validated by comparing with the experimental results in the cavitation water tunnel at the Korea Ocean Research & Development Institute. The results show that this solver is highly suitable for simulating the cavitating flows. After the code validation, the cavity length with changes of water depth, angle of attack and velocity were obtained.. Cavitation inception was also calculated for various operational conditions.
COMPUTATIONAL ASSESSEMENT OF OPTIMAL FLOW RATE FOR STABLE FLOW IN A VERTICAL ROTATING DISk CHEMICAL VAPOR DEPOSITION REACTOR
Kwak, H.S. ;
Journal of computational fluids engineering, volume 17, issue 1, 2012, Pages 86~93
DOI : 10.6112/kscfe.2012.17.1.086
A numerical investigation is conducted to search for the optimal flow rate for a rotating-disk chemical vapor decomposition reactor operating at a high temperature and a low pressure. The flow of a gas mixture supplied into the reactor is modeled by a laminar flow of an ideal gas obeying the kinetic theory. The axisymmetric two-dimensional flow in the reactor is simulated by employing a CFD package FLUENT. With operating pressure and temperature fixed, numerical computations are performed by varying rotation rate and flow rate. Examination of the structures of flow and thermal fields leads to a flow regime diagram illustrating that there are a stable plug-like flow regime and a few unfavorable flow regimes induced by mass unbalance or buoyancy. The criterion for sustaining a plug-like flow regime is discussed based on a theoretical scaling argument. Interpretation of the flow regime map suggests that a favorable flow is attainable with a minimum flow rate at the smallest rotation rate guaranteeing the dominance of rotation effects over buoyancy.
CAVITATION FLOW SIMULATION FOR A 2-D HYDROFOIL USING A HOMOGENEOUS MIXTURE MODEL ON UNSTRUCTURED MESHES
Ahn, S.J. ; Kwon, O.J. ;
Journal of computational fluids engineering, volume 17, issue 1, 2012, Pages 94~100
DOI : 10.6112/kscfe.2012.17.1.094
In this paper, the cavitating flows around a hydrofoil have been numerically investigated by using a 2-d multi-phase RANS flow solver based on pseudo-compressibility and a homogeneous mixture model on unstructured meshes. For this purpose, a vertex-centered finite-volume method was utilized in conjunction with 2nd-order Roe's FDS to discretize the inviscid fluxes. The viscous fluxes were computed based on central differencing. The Spalart-Allmaras one equation model was employed for the closure of turbulence. A dual-time stepping method and the Gauss-Seidel iteration were used for unsteady time integration. The phase change rate between the liquid and vapor phases was determined by Merkle's cavitation model based on the difference between local and vapor pressure. Steady state calculations were made for the modified NACA66 hydrofoil at several flow conditions. Good agreements were obtained between the present results and the experiment for the pressure coefficient on a hydrofoil surface. Additional calculation was made for cloud cavitation around the hydrofoil. The observation of the vapor structure, such as cavity size and shape, was made, and the flow characteristics around the cavity were analyzed. Good agreements were obtained between the present results and the experiment for the frequency and the Strouhal number of cavity oscillation.