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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 2, Issue 2 - Dec 1997
Volume 2, Issue 1 - Apr 1997
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Numerical calculation of Laminar flow in a Square Duct of 90° Bend
Kim H. T. ; Kim J. J. ;
Journal of computational fluids engineering, volume 2, issue 1, 1997, Pages 1~7
A FA-FD hybrid method, developed for solving three-dimensional incompressible Navier-Stokes equations, is applied to calculate three-dimensional laminar flows through a square duct with a 90° bend. The method discretizes the convective terms in the primary flow direction with 3rd-order upwind finite-differences and the convective and diffusive terms in the transverse directions with the two-dimensional finite analytic method. The non-staggered grid system is used and the pressure-velocity coupling is achieved by a global iteration procedure based on the PISO algorithm. Detailed comparisons between the computed solutions and the available experimental data are given mainly for the velocity distributions at cross-sections in a 90° bend of a square duct with both fully developed and developing entry flows. Although the computational result shows generally a good agreement with the experimental data, there are some significant discrepancies underlining the necessity of more accurate numerical methods as well as reliable experimental data for their validation.
Development of a Three-Dimensional Euler Solver for Analysis of Basic Contraction Flow
Kim J. ; Kim H. T. ;
Journal of computational fluids engineering, volume 2, issue 1, 1997, Pages 8~12
The three-dimensional Euler equations are solved numerically for the analysis of contraction flows in wind or water tunnels. A second-order finite difference method is used for the spatial discretization on the nonstaggered grid system and the 4-stage Runge-Kutta scheme for the numerical integration in time. In order to speed up the convergence, the local time stepping and the implicit residual-averaging schemes are introduced. The pressure field is obtained by solving the pressure-Poisson equation with the Neumann boundary condition. For the evaluation of the present Euler solver, numerical computations are carried out for three contraction geometries, one of which was adopted in the Large Cavitation Channel for the U.S. Navy. The comparison of the computational results with the available experimental data shows good agreement
Numerical Simulations of Nonlinear Waves Generated by Submerged Bodies
Kang Kuk-Jin ;
Journal of computational fluids engineering, volume 2, issue 1, 1997, Pages 13~20
A fundamental study for the numerical scheme to simulate unsteady nonlinear waves by solving Euler equations is presented. First a conservation form and a non-conservation form of the Euler equations with a free surface fitted coordinate system are compared. Next, a time splitting fractional step method and an alternating direction implicit(ADI) method for the time integration are compared. For the comparative study, flow calculations around a bottom bump in a channel and a NACA 0012 hydrofoil in a flume are performed. The results show that the ADI method with a third order upwind differencing scheme is very efficient in reducing the computing time with keeping the accuracy, And, there is no distinct difference between two expression forms except that the non-conservative form shows faster wave propagating velocity than the conservation form. Some results are compared with experiments and show good agreement.
Numerical Simulation of 2-D Estuaries and Coast by Multi-Domain and the Interpolating Matrix Method
Chae H. S. ;
Journal of computational fluids engineering, volume 2, issue 1, 1997, Pages 21~28
This paper presents a two-dimensional horizontal implicit model to general circulation in estuaries and coastal seas. The model is developed in non-orthogonal curvilinear coordinates system, using the Interpolating Matrix Method (IMM), in combination with a technique of multi-domain. In the propose model, the Saint-Venant equations are solved by a splitting-up technique, in the successive steps; convection, diffusion and wave propagation. The ability of the proposed model to deal with full scale nature is illustrated by the interpretation of a dye-tracing experiment in the Gironde estuary.
Calculation of Near and Far Acoustic Fields Due to a Spinning Vortex Pair in Free Field
Koo Sam-Ok ; Ryu Ki-Wahn ; Lee Duck-Joo ;
Journal of computational fluids engineering, volume 2, issue 1, 1997, Pages 29~36
Sound Generation Due to a Spinning Vortex Pair Near the Flat Wall
Koo Sam-Ok ; Ryu Ki-Wahn ; Lee Duck-Joo ;
Journal of computational fluids engineering, volume 2, issue 1, 1997, Pages 37~45
Incompressible Viscous Flow Analysis Around a Three Dimensional Minivan-Like Body
Jung Y. R. ; Park W. G. ; Park Y. J. ; Kim J. S. ; Hong S. H. ;
Journal of computational fluids engineering, volume 2, issue 1, 1997, Pages 46~53
The flow field around a three dimensional minivan-like body has been simulated. This study solves 3-D unsteady incompressible Navier-Stokes equations on a non-orthogonal curvilinear coordinate system using second-order accurate schemes for the time derivatives, and third/second-order scheme for the spatial derivatives. The Marker-and-Cell concept is applied to efficiently solve continuity equation. A H-H type of multi-block grid system is generated around a three dimensional minivan-like body. Turbulent flows have been modeled by the Baldwin-Lomax turbulent model. To validate present procedure, the flows around the Ahmed body with 12.5° of slant angle are simulated. A good agreement with other numerical results is achived. After code validation, the flows around a mimivan-like body are simulated. The simulation shows three dimensional vortex-pair just behind body. The flow separation is also observed on the rear of the body. It has concluded that the results of present study properly agreed with physical flow phenomena.
Analysis of New DI Diesel Combustion Chamber System using New Spray Wall Impaction Model
Chang W. S. ; Kim D. J. ; Park K. ;
Journal of computational fluids engineering, volume 2, issue 1, 1997, Pages 54~65
Wall wetting in diesel engines has been considered as a bad phenomenon because of fuel deposition which makes fuel/air mixing and evaporation worse. In order to avoid the problem, many research works have been carried out. One of the studies is on new combustion chamber systems which are using spray impacting on a wall. In this study a new type of chamber system is analysed using wall impaction model introduced and assessed in the coupled paper. The gas phase is modelled in terms of the Eulerian continuum conservation equations of mass, momentum, energy and fuel vapour fraction, The liquid phase is modelled following the discrete droplet model approach in Lagrangian form. With various conditions the spray distribution, vapor contour and gas flows are analyzed, and then design factors of those combustion systems are recommended.
Implicit/Explicit Finite Element Method for Euler Flows Inside the Optimum Nozzle
Yoon W. S. ; Kho H. ;
Journal of computational fluids engineering, volume 2, issue 1, 1997, Pages 66~72
Optimum nozzle design exploiting the method of characteristic(M.O.C) has been in application as an efficient design methodology targeting a less weighted and short expansion nozzle. This paper treats the optimum nozzle design and the analysis of the inviscid compressible flow inside. Based on traditional Rao's method, the optimum nozzle design is coded with minor modifications for the identification of the control surface across which the mass flux should be conserved. Internal flow field is simulated numerically by M.O.C and implicit/explicit Taylor-Galerkin finite element method(F.E.M) with the aid of adaptive remeshing to capture the shock wave, hence improve the accuracy. Designed and calculated flow fields due to the separate analyses show that the mass flux predicted by optimum nozzle design with M.O.C is not conserved across the control surface and the sonic line should be located upstream of the nozzle throat. Rao's optimum nozzle design methodology exaggerates the momentum thrust and tends to overemphasize the engine performance loss.
An Evaluation of Recent Higher-order Bounded Convection Schemes
Choi Seok Ki ; Lee Yong Bum ;
Journal of computational fluids engineering, volume 2, issue 1, 1997, Pages 73~83
A Grid Generation Technique for the External Flow Fields Utilizing the Predictor-Corrector Scheme
Kim B. S. ;
Journal of computational fluids engineering, volume 2, issue 1, 1997, Pages 84~92
In this paper a new structured grid generation technique is introduced. This new technique utilizes predictor-corrector approach, and is a marching scheme in the global sense as the hyperbolic scheme is. In the predictor step, one layer of grid cells is obtained by using Modified Advancing Front Method which generates a collection of quadrilateral cells simultaneously. In the corrector step, the layer of grid cells that is calculated in the predictor step is adjusted by solving Laplace equations to prevent grid lines from skewing and overlapping in highly curved configurations. It is shown that the resultant algorithm, named a MAP scheme, which combines the Modified Advancing Front Method as a Predictor with an elliptic scheme as a corrector can be used to generate globally smooth and locally near-orthogonal grids for external flow fields even for highly curved configurations. Examples of grid generations for external flow fields about several configurations by use of the present approach are given, and its applicability and flexibility have been demonstrated and discussed.
A Numerical Study On Various Energy and Environmental Systems(Ⅰ) : LPG dispersion, Lake flow, Primary clarifier, Hood ventilation, Cyclone combustor, Dow chlorination reactor.
Jang Dong-Sun ; Kim Gyeong-Mi ; Lee Eun-Ju ; Park Byeong-Su ; Kim Bok-Sun ;
Journal of computational fluids engineering, volume 2, issue 1, 1997, Pages 93~108
This paper describes several computational results on the various energy and environmental problems using Patankar's SIMPLE method. The specific problems included in this study are : pollutant and flammable material dispersions in open and confined areas, buoyancy-driven flow in a lake, primary clarifier for water and waste water treatment, hood ventilation in workplace. cyclone combustor and Dow chlorination reactor. A control-volume based finite-difference method is employed together with the power-law scheme. The pressure-velocity coupling is resolved by the use of the revised version of SIMPLE, says SIMPLER and SIMPLEC. The Reynolds stresses are closed using the standard or RNG κ-ε models. A nonequilibrium turbulent reaction model is developed for the application of the chlorination process in the Dow thermal reactor. Other important empirical models and physical insights appeared in this study are presented and discussed in a brief note. The computational method developed in this study is considered, in general, as a viable tool for the design and determination of the optimal operating condition of various environmental engineering system of interest.
A Study on the Development of Air Pollution Model Applicable to the Complex Terrain
Yoon J. Y. ; Yi S. C. ; Hong M. S. ;
Journal of computational fluids engineering, volume 2, issue 1, 1997, Pages 109~116
The objective of this paper is to develop a computational model for the prediction of the pollutant spread from a mass source over a complex terrain. The model comprises a two-dimensional, steady state flow model and a concentration model which employs the results of the computed flow field. The computational model is applied to predict the spread of pollutants for Sanbon city, and the two cases have been compard with the results of SF/sub 6/ trace experiments.
CFD aided design of the continuous casting tundish
Cho J. R. ; Ha M. Y. ; Lee S. W. ;
Journal of computational fluids engineering, volume 2, issue 1, 1997, Pages 117~128
Effects of dam and weir on the fluid flow and behavior of inclusions in the continuous casting tundish have been studied using the CFD (Computational Fluid Dynamics) technique. Inclusions affecting the quality of steel products have been considered to be passive: the fluid flow has been obtained for unstaggered grid points defined on body-fitted generalized cuvilinear coordinates with no attention on inclusions, and the spatial propagation of inclusions has been determined by using the flow field data. The result show that the dam and weir direct the flow to the free surface and increase the residence time of inclusions significantly, and thereby that inclusions have much more chance to be floated to the free surface of the tundish where it is eliminated. It is also found that they offer more margin on the geometric design of exit nozzles connected to moulds. This finding is particularly important for twin casting operations where the quality of steel products from the two moulds be kept uniformly.
Free surface flow of a Two-Layer fluid over a bump - Hydraulic Fall
Choi J. W. ;
Journal of computational fluids engineering, volume 2, issue 1, 1997, Pages 129~137
We consider long nonlinear waves in the two-layer flow of an inviscid and incompressible fluid bounded above by a free surface and below by a rigid boundary. The flow is forced by a bump on the bottom. The derivation of the forced KdV equation fails when the density ratio h and the depth ratio ρ yields a condition 1＋hρ=(2-h)((1-h)²＋4ρh)/sup 1/2/. To overcome this difficulty we derive a forced modified KdV equation by a refined asymptotic method. Numerical solutions are given and hydraulic fall solution of a two layer fluid is expressed analytically in the case that derivation of the forced KdV(FKdV) equaition fails.