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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 12, Issue 4 - Dec 2007
Volume 12, Issue 3 - Sep 2007
Volume 12, Issue 2 - Jun 2007
Volume 12, Issue 1 - Mar 2007
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A STUDY ABOUT FLOW CONTROL CHARACTERISTICS USING A SYNTHETIC JET
Hong, Woo-Ram ; Kim, Sang-Hoon ; Kim, Woo-Re ; Kim, Yu-Shin ; Kim, Chong-Am ;
Journal of computational fluids engineering, volume 12, issue 2, 2007, Pages 1~7
To develop an aerodynamic performance, two groups of studies have been achieved widely. One is about the geometric design of vehicles and the other is about aerodynamic devices. Geometric design is a credible and stable method. However, it is not flexible and each part is related interactively. Therefore, if one part of geometry is modified, the other part will be required to redesign. On the other hand, the flow control by aerodynamic devices is flexible and modulized method. Even though it needs some energy, a relatively small amount of input makes more advanced aerodynamic performance. Synthetic jet is one of the method in the second group. The device repeats suctions and blowing motions in constant frequency. According to the performance, the adjacent flow to flight surface are served momentum. This mechanism can reduce the aerodynamic loss of boundary layer and separated flow. A synthetic jet actuator has several parameters, which influences the flow control. This study focuses on the parameter effects of synthetic jet - orifice geometry, frequency, jet speed and etc.
DEVELOPMENT OF GENERAL PURPOSE THERMO/FLUID FLOW ANALYSIS PROGRAM NUFLEX
Hur, Nahm-Keon ; Won, Chan-Shik ; Ryou, Hong-Sun ; Son, Gi-Hun ; Kim, Sa-Ryang ;
Journal of computational fluids engineering, volume 12, issue 2, 2007, Pages 8~13
A general purpose program NUFLEX for the analysis 3-D thermo/fluid flow and pre/post processor in complex geometry has been developed, which consists of a flow solver based on FVM and GUI based pre/post processor. The solver employs a general non-orthogonal grid system with structured grid and solves laminar and turbulent flows with standard/RNG
turbulence model. In addition, NUFLEX is incorporated with various physical models, such as interfacial tracking, cavitation, MHD, melting/solidification and spray models. For the purpose of evaluation of the program and testing the applicability, many actual problems are solved and compared with the available data. Comparison of the results with that by STAR-CD or FLUENT program has been also made for the same flow configuration and grid structure to test the validity of NUFLEX.
AN IMMERSED BOUNDARY METHOD WITH FEEDBACK FORCING FOR SIMULATION OF FLOW AROUND AN ARBITRARILY MOVING BODY
Shin, S.J. ; Huang, W.X. ; Sung, H.J. ;
Journal of computational fluids engineering, volume 12, issue 2, 2007, Pages 14~20
We present an improved immersed boundary method for computing incompressible viscous flow around an arbitrarily moving body on a fixed computational grid. The main idea is to incorporate feedback forcing scheme of virtual boundary method with Peskin's regularized delta function approach in order to use large CFL number and transfer quantities between Eulerian and Lagrangian domain effectively. From the analysis of stability limits and effects of feedback forcing gains, optimum regions of the feedback forcing are suggested.
NUMERICAL ANALYSIS OF MULTIPHASE FLOW BY NUFLEX
Yu, Tae-Jin ; Suh, Young-Ho ; Son, Gi-Hun ; Hur, Nahm-Keon ;
Journal of computational fluids engineering, volume 12, issue 2, 2007, Pages 21~25
A general purpose program NUFLEX has been extended for two-phase flows with topologically complex interface and cavitation flows with liquid-vapor phase change caused by large pressure drop. In analysis of two-phase flow, the phase interfaces are tracked by employing a LS(Level Set) method. Compared with the VOF(Volume-of-Fluid) method based on a non-smooth volume-fraction function, the LS method can calculate an interfacial curvature more accurately by using a smooth distance function. Also, it is quite straightforward to implement for 3-D irregular meshes compared with the VOF method requiring much more complicated geometric calculations. Also, the cavitation process is computed by including the effects of evaporation and condensation for bubble formation and collapse as well as turbulence in flows. The volume-faction and continuity equations are adapted for cavitation models with phase change. The LS and cavitation formulation are implemented into a general purpose program for 3-D flows and verified through several test problems.
COMPARISON OF THE TREATMENTS OF TURBULENT HEAT FLUX FOR NATURAL CONVECTION WITH THE ELLIPTIC-BLENDING SECOND-MOMENT CLOSURE
Choi, Seok-Ki ; Kim, Seong-O ;
Journal of computational fluids engineering, volume 12, issue 2, 2007, Pages 26~31
A comparative study on the treatment of the turbulent heat flux with the elliptic blending second-moment closure for a natural convection flow is performed. Three cases of different treating the turbulent heat flux are considered. Those are the generalized gradient diffusion hypothesis (GGDH), the algebraic flux model (AFM) and the differential flux model (DFM). The constants in the models are adjusted with a primary emphasis placed on the accuracy of predicting the local Nusselt number. These models are implemented in a computer code specially designed for evaluation of turbulent models. Calculations are performed for a turbulent natural convection in the 1:5 rectangular cavity and the calculated results are compared with the available experimental data. The results show that the three models produce nearly the same accuracy of solutions. These results show that the GGDH, AFM and DFM models for treating the turbulent heat flux are sufficient for this simple shear flow where the shear production is dominant. It is observed that, in the weakly stratified region at the center zone of the cavity, the vertical velocity fluctuation is nearly zero in the GGDH solutions, which shows that the GGDH model may not be suitable for the strongly stratified flow. Thus, further study on the strongly stratified flow should be followed.
NUMERICAL ANALYSIS OF PHASE CHANGE AND SPRAY, MHD FLOW USING A NUFLEX
Ro, Kyoung-Chul ; Ryou, Hong-Sun ; Kang, Kwan-Gu ; Hur, Nahm-Keon ;
Journal of computational fluids engineering, volume 12, issue 2, 2007, Pages 32~36
NUFLEX is a general purpose program for the analysis 3D thermo/fluid flow and pre/post processor in a complex geometry. NUFLEX is composed of various physical models, such as phase change(solidification/melting) and spray, MHD(Magneto Hydraulic Dynamics) models. It is possible to simulate continuous cast iron process and spray droplet breakup/collision phenomenon. For the verification of these models, compared with the experimental data and commercial CFD code's results. The results show good agreements with experimental and comercial CFD codes's results.
NUMERICAL SIMULATION ON FLUID-STRUCTURE INTERACTION OF A TWO-DIMENSIONAL ORBITING FLEXIBLE FOIL
Shin, Sang-Mook ;
Journal of computational fluids engineering, volume 12, issue 2, 2007, Pages 37~45
The hybrid Cartesian/immersed boundary method is applied to simulate fluid-structure interaction of a two-dimensional orbiting flexible foil. The elastic deformation of the flexible foil is modelled based on the dynamic equation of a thin-plate. At each time step, the locations and velocities of the Lagrangian control points on the flexible foil are used to reconstruct the boundary conditions for the flow solver based on the hybrid staggered/non-staggered grid. To test the developed code, the flow fields around a flapping elliptical wing are calculated. The time history of the vertical force component and the evolution of the vorticity fields are compared with recent other computations and good agreement is achieved. For the orbiting flexible foil, the vorticity fields are compared with those of the case without the deformation. The combined effects of the angle of attack and the orbit on the deformation are investigated. The grid independency study is carried out for the computed time history of the deformation at the tip.
INTERNAL FLOW PROPERTIES AND THRUST CHARACTERISTICS OF AXI-SYMMETRIC ANNULAR BELL TYPE EJECTOR-JET
Park, G.H. ; Kwon, S.J. ;
Journal of computational fluids engineering, volume 12, issue 2, 2007, Pages 46~52
An experimental and numerical investigation of the ejector-jets focusing on its geometric parameters that effect on thrust performance was carried out. The area ratio of the primary nozzle that was tested in the present study was 2.17 and 3.18, while the ratio of the length to the diameter of the duct downstream the primary nozzle inlet had values of 3.41, 6.82, and 10.23. Internal flow properties of ejector-jet were estimated by comparison experiment data and CFD analysis for basic study of ejector-jet thrust performance. For examination of thrust performance, the thrust ratios increased with increase in L/D. Especially at AR=2.17, the maximum thrust augmentation was 33 percent for the shortest L/D. It is expected that the increase of mixing duct length of ejector-jet will be helpful in a thrust performance by improving mixing efficiency.
GAS-LIQUID TWO-PHASE HOMOGENEOUS MODEL FOR CAVITATING FLOW
Shin, Byeong-Rog ;
Journal of computational fluids engineering, volume 12, issue 2, 2007, Pages 53~62
A high resolution numerical method aimed at solving cavitating flow is proposed and applied to gas-liquid two-phase shock tube problem. The present method employs a finite-difference 4th-order Runge-Kutta method and Roe's flux difference splitting approximation with the MUSCL TVD scheme. By applying the homogeneous equilibrium cavitation model, the present density-based numerical method permits simple treatment of the whole gas-liquid two-phase flow field, including wave propagation and large density changes. The speed of sound for gas-liquid two-phase media is derived on the basis of thermodynamic relations and compared with that by eigenvalues. By this method, a Riemann problem for Euler equations of one dimensional shock tube was computed. Numerical results such as detailed observations of shock and expansion wave propagations through the gas-liquid two-phase media at isothermal condition and some data related to computational efficiency are made. Comparisons of predicted results and exact solutions are provided and discussed.