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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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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 14, Issue 4 - Dec 2009
Volume 14, Issue 3 - Sep 2009
Volume 14, Issue 2 - Jun 2009
Volume 14, Issue 1 - Mar 2009
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TRANSIENT SIMULATION OF SOLID PARTICLE DISTRIBUTION WITH VARIOUS DESIGN PARAMETERS OF THE BAFFLE IN A STIRRED TANK
Kim, Chi-Gyeom ; Lee, Seung-Jae ; Won, Chan-Shik ; Hur, Nahm-Keon ;
Journal of computational fluids engineering, volume 14, issue 4, 2009, Pages 1~6
In the present study, numerical simulations were performed in a stirred solid/liquid system by using Eulerian multi-phase model. The transient flow field of liquid and distribution of solid particles were predicted in the stirred tank with pitched paddle impeller and baffles. The Frozen rotor method is adopted to consider the rotating motion of the impeller. The effects of number and width of baffles on the mixing time and the quality of solid suspension in the stirred tank are presented numerically. The result shows that the mixing time decreases as the width and number of baffles increase. The present numerical methodology can be applied to optimizing mixing condition of industrial mixer.
VERIFICATION OF FIN EFFICIENCY THEORY FOR THE CIRCULAR FINNED-TUBE HEAT EXCHANGER BY NUMERICAL EXPERIMENT
Kang, H.C. ; Lim, B.B. ; Lee, J.H. ;
Journal of computational fluids engineering, volume 14, issue 4, 2009, Pages 7~12
The purpose of the present study is to investigate the convective heat transfer characteristics and the validity of fin efficiency of the circular finned-tube heat exchanger by using commercial CFD code. The heat transfer coefficient obtained by using the laminar model was 22% overestimated to the experimental data. The fin surface temperature compared with the experimental data measured by the liquid crystal method. The fin efficiency by the present numerical experiment, defined as normalized and averaged fin surface temperature, was greater than the theoretical fin efficiency and the difference is increased at high value of the factor
IMPLEMENTATION OF A SECOND-ORDER INTERPOLATION SCHEME FOR THE CONVECTIVE TERMS OF A SEMI-IMPLICIT TWO-PHASE FLOW ANALYSIS SOLVER
Cho, H.K. ; Lee, H.D. ; Park, I.K. ; Jeong, J.J. ;
Journal of computational fluids engineering, volume 14, issue 4, 2009, Pages 13~22
A two-phase (gas and liquid) flow analysis solver, named CUPID, has been developed for a realistic simulation of transient two-phase flows in light water nuclear reactor components. In the CUPID solver, a two-fluid three-field model is adopted and the governing equations are solved on unstructured grids for flow analyses in complicated geometries. For the numerical solution scheme, the semi-implicit method of the RELAP5 code, which has been proved to be very stable and accurate for most practical applications of nuclear thermal hydraulics, was used with some modifications for an application to unstructured non-staggered grids. This paper is concerned with the effects of interpolation schemes on the simulation of two-phase flows. In order to stabilize a numerical solution and assure a high numerical accuracy, the second-order upwind scheme is implemented into the CUPID code in the present paper. Some numerical tests have been performed with the implemented scheme and the comparison results between the second-order and first-order upwind schemes are introduced in the present paper. The comparison results among the two interpolation schemes and either the exact solutions or the mesh convergence studies showed the reduced numerical diffusion with the second-order scheme.
NUMERICAL SIMULATIONS OF SUPERSONIC FLOWS USING POROUS AND ROUGH WALL BOUNDARY CONDITIONS
Kwak, E.K. ; Yoo, I.Y. ; Lee, D.H. ; Lee, S. ;
Journal of computational fluids engineering, volume 14, issue 4, 2009, Pages 23~30
The existing code which solves two-dimensional RANS(Reynolds Averaged Navier-Stokes) equations and 2-equation turbulence model equations was modified to enable numerical simulation of various supersonic flows. For this, various boundary conditions have been implemented to the code. Bleed boundary condition was incorporated into the code for calculating wall mean flow quantities. Furthermore, boundary conditions for the turbulence quantities along rough surfaces as well as porous walls were applied to the code. The code was verified and validated by comparing the computational results against the experimental data for the supersonic flows over bleed region on a flat plate. Furthermore, numerical simulations for supersonic shock boundary layer interaction with a bleed region were performed and their results were compared with the existing computational results.
A NOVEL METHOD FOR REFINING A META-MODEL BY PARETO FRONTIER
Jo, S.J. ; Chae, S.H. ; Yee, K.J. ;
Journal of computational fluids engineering, volume 14, issue 4, 2009, Pages 31~40
Although optimization by sequentially refining metamodels is known to be computationally very efficient, the metamodel that can be used for this purpose is limited to Kriging method due to the difficulties related with sample points selections. The present study suggests a novel method for sequentially refining metamodels using Pareto Frontiers, which can be used independent of the type of metamodels. It is shown from the examples that the present method yields more accurate metamodels compared with full-factorial optimization and also guarantees global optimum irrespective of the initial conditions. Finally, in order to prove the generality of the present method, it is applied to a 2D transonic airfoil optimization problem, and the successful design results are obtained.
APPLICATION OF AN IMMERSED BOUNDARY METHOD FOR THREE-DIMENSIONAL FLOQUET STABILITY ANALYSIS
Yoon, D.H. ; Yang, K.S. ;
Journal of computational fluids engineering, volume 14, issue 4, 2009, Pages 41~47
An immersed boundary method(IBM, Kim et al.(2001)) for simulating flows over complex geometries is applied to computation of three-dimensional Floquet stability of a periodic wake. Floquet stability analysis is employed to extract different modes of three-dimensional instability. To verify the present method, a fully-resolved Floquet stability calculation for flow past a circular cylinder is considered. There are two different instability modes with long(mode A) and short (mode B) spanwise wavelengths for the periodic wake of a circular cylinder. The critical Reynolds number and the most unstable spanwise wavelengths of modes A and B are computed using the present method, and compared with other authors' results currently available.
A NUMERICAL STUDY ON THE ROLL LOCK-IN OF A CANARD-CONTROLLED MISSILE WITH FREELY SPINNING TAILFINS
Yang, Y.R. ; Kim, M.S. ; Myong, R.S. ; Cho, T.H. ;
Journal of computational fluids engineering, volume 14, issue 4, 2009, Pages 48~55
In this study, roll lock-in phenomena of freely spinning tailfins were investigated by a CFD code. To analyze a motion of freely spinning tailfins, this research use a Chimera method, an Euler code and a 6 degrees of freedom analysis. The numerical results of aerodynamic characteristics and roll rates of a canard-controlled missile with freely spinning tailfins show a good agreement with wind tunnel test results. Using the roll rates calculation result of freely spinning tailfins, roll lock-in phenomena is confirmed. Roll lock-in phenomena and Roll lock-in states can be predicted through effects of the induced vortex of the canards control and the analysis of the rolling moments of tailfins due to the bank angle.
NUMERICAL INVESTIGATION ON HYDRODYNAMIC LUBRICATION CHARACTERISTICS OF MICRO DIMPLE TEXTURED SURFACES
Hong, Sa-Hoon ; Lee, Jae-Ung ; Cho, Min-Haeng ; Lee, Seong-Hyuk ;
Journal of computational fluids engineering, volume 14, issue 4, 2009, Pages 56~61
This study deals with the numerical investigation on two-dimensional lubrication characteristics of micro-dimple shapes fabricated on solid surfaces by using the commercial CFD code (Fluent V.6.3) to examine the influence of micro dimple depth and width on the reduction in friction under the sliding plate condition. In addition, single and multiple dimple arrays are simulated, all for a fixed area fraction of dimple on the surface. As a result, it is found that the existence of micro-dimpled surface makes it possible to substantially reduce the friction forces exerted on the surfaces, and such an optimum dimple depth would be present because the dimple depth larger than the optimum value did no longer affect the reduction in shear stresses, indicating that the reduction of friction is likely to be associated with inner flows of lubricant inside dimples. Moreover, it is observed that at the fixed area fraction, the friction reduction increases with the increase of dimple diameter.
A NUMERICAL STUDY ON THE CONTROL OF PARTICLE CONCENTRATION DISTRIBUTION IN A PIPE
Yi, Min-Young ; Yoo, Joo-Sik ;
Journal of computational fluids engineering, volume 14, issue 4, 2009, Pages 62~66
The control of particle concentration distribution in a pipe with an orifice and a sheath air is numerically investigated. When using Eulerian approach, there is no great change in the concentration distribution by the shape of orifice and molecular diffusivity. As the Reynolds number becomes small, the effect of orifice on the concentration distribution is decreased. For small Reynolds number, the concentration distribution can be effectively controlled by using a sheath air. The effect of the sheath air on the concentration distribution is increased, as the Reynolds number becomes small.
COMPUTATIONS OF NATURAL CONVECTION FLOW WITHIN A SQUARE CAVITY BY HERMITE STREAM FUNCTION METHOD
Kim, J.W. ;
Journal of computational fluids engineering, volume 14, issue 4, 2009, Pages 67~77
This paper is a continuation of a recent development on the Hermite-based divergence-free element method and deals with a non-isothermal fluid flow driven by the buoyancy force in a square cavity with temperature difference across the two sides. Two Hermite functions are considered for numerical computations in this paper. One is a cubic function and the other is a quartic function. The degrees-of-freedom of the cubic Hermite function are stream function and its first and second derivatives for the velocity field, and temperature and its first derivatives for the temperature field. The degrees-of-freedom of the quartic Hermite function include two second derivatives and one cross derivative of the stream function in addition to the degrees-of-freedom of the cubic stream function. This paper presents a brief review on the Hermite based divergence-free basis functions and its finite element formulations for the buoyancy driven flow. The present algorithm does not employ any upwinding or a stabilization term. However, numerical values and contour graphs for major flow variables showed good agreements with those by De Vahl Davis.
SIMULATION OF CAVITATING FLOW PAST CYLINDERS WITH STRONG SIDE-FLOW
Lee, B.W. ; Park, W.G. ; Lee, K.C. ;
Journal of computational fluids engineering, volume 14, issue 4, 2009, Pages 78~85
Cavitating flow simulation is of practical importance for many engineering systems, such as marine propellers, pump impellers, nozzles, injectors, torpedoes, etc. The present work has focused on the simulation of cavitating flow past cylinders with strong side flows. The governing equation is the Navier-Stokes equation based on the homogeneous mixture model. The momentum and energy equation is in the mixture phase while the continuity equation is solved liquid and vapor phase, separately. An implicit dual time and preconditioning method are employed for computational analysis. For the code validation, the results from the present solver have been compared with experiments and other numerical results. A fairly good agreement with the experimental data and other numerical results have been obtained. After the code validation, the strong side flow was applied to include the wake flow effects of the submarine or ocean tide.
A STUDY ON THE DEVELOPMENT OF ONE-DIMENSIONAL GUI PROGRAM FOR MICROFLUIDIC-NETWORK DESIGN
Park, I.H. ; Kang, S. ; Suh, Y.K. ;
Journal of computational fluids engineering, volume 14, issue 4, 2009, Pages 86~92
Nowadays, the development of microfluidic chip [i.e. biochip, micro-total analysis system (
-TAS) and LOC (lab-on-a-chip)] becomes more active, and the microchannels to deliver fluid by pressure or electroosmotic forces tend to be more complex like electronic circuits or networks. For a simple network of channels, we may calculate the pressure and the flow rate easily by using suitable formula. However, for complex network it is not handy to obtain such information with that simple way. For this reason, Graphic User Interface (GUI) program which can rapidly give required information should be necessary for microchip designers. In this paper, we present a GUI program developed in our laboratory and the simple theoretical formula used in the program. We applied our program to simple case and could get results compared well with other numerical results. Further, we applied our program to several complex cases and obtained reasonable results.
NUMERICAL STUDY ON TWO-DIMENSIONAL INCOMPRESSIBLE VISCOUS FLOW BASED ON GRIDLESS METHOD
Jeong, S.M. ; Park, J.C. ; Heo, J.K. ;
Journal of computational fluids engineering, volume 14, issue 4, 2009, Pages 93~100
The gridless (or meshfree) methods, such as MPS, SPH, FPM an so forth, are feasible and robust for the problems with moving boundary and/or complicated boundary shapes, because these methods do not need to generate a grid system. In this study, a gridless solver, which is based on the combination of moving least square interpolations on a cloud of points with point collocation for evaluating the derivatives of governing equations, is presented for two-dimensional unsteady incompressible Navier-Stokes problem in the low Reynolds number. A MAC-type algorithm was adopted and the Poission equation for the pressure was solved successively in the moving least square sense. Some typical problems were solved by the presented solver for the validation and the results obtained were compared with analytic solutions and the numerical results by conventional CFD methods, such as a FVM.
DIRECT NUMERICAL SIMULATION OF PARTICLE SUSPENSIONS IN A POLYMERIC LIQUID
Hwang, W.R. ; Hulsen, M.A. ; Meijer, H.E.H. ;
Journal of computational fluids engineering, volume 14, issue 4, 2009, Pages 101~108
We present a new finite-element scheme for direct numerical simulation of particle suspensions in simple shear flow of a viscoelastic fluid in 3D. The sliding tri-periodic representative cell concept has been combined with DEVSS/DG finite element scheme by introducing constraint equations along the domain boundary. Rigid body motion of the freely suspended particle is described by the rigid-shell description and implemented by Lagrangian multipliers on particle boundaries. We present the bulk rheology of suspensions through the numerical examples of single-, two- and many-particle problems, which represent a large number of such systems in simple shear flow. We report the steady bulk viscosity and the first normal stress coefficient, which show shear-thickening behavior for both properties.