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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 13, Issue 4 - Dec 2008
Volume 13, Issue 3 - Sep 2008
Volume 13, Issue 2 - Jun 2008
Volume 13, Issue 1 - Mar 2008
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A STUDY ON THE FLOW CHARACTERISTICS OF AIR-KNIFE USING A CONSTANT EXPANSION RATE NOZZLE
Lee, Dong-Won ; Kang, Nam-Cheol ; Kim, Guen-Young ; Kwon, Young-Doo ; Kwon, Soon-Bum ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 1~7
In the process of continuous hot-dip galvanizing, it is well known that the gas wiping through an air knife system is most effective because of its uniformity in coating thickness, possibility of thin coating, workability in high speed, and simplicity of control. However, gas wiping used in the galvanizing process brings about a problem of splashing at the strip edge above a certain high speed of process. It is also known that the problem of edge splashing is more harmful than that at the mid strip surface. For a given liquid(of a certain viscosity and surface tension), the onset of splashing mainly depends upon the strip velocity, the gas-jet pressure, and the nozzle's stand-off distance. In these connections in the present study, we proposed three kinds of air knife system having nozzles of constant expansion rate, and compared the jet structures issuing from newly proposed nozzle systems with the result by a conventional one. In numerical analysis, the governing equations are consisted of two-dimensional time dependent Navier-Stokes equations, and the standard k-
turbulence model is employed to solve turbulence stress and so on. As the result, it is found that we had better use the constant expansion-rate nozzle which can be interpreted from the point view of the energy saving for the same coating thickness. Also, we better reduce the size of separation bubble and enhance the cutting ability at the strip surface, by using an air-knife having constant expansion-rate nozzle.
PERFORMANCE EVALUATION OF PASSENGERS' EVACUATION FOR SMOKE-CONTROL MODES IN A SUBWAY STATION
Park, Won-Hee ; Chang, Hee-Chul ; Jung, Woo-Sung ; Lee, Han-Su ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 8~12
Heat/smoke detectors are installed in most subway platforms in Korea to detect fire. Subway platform is divided by smoke-control zones for efficient smoke-control. Once the detectors detect heat or smoke, the smoke-control ventilation system in the platform and concourse is activated according to the smoke-control ventilation mode. Smoke-control mode during fires in Korean subway platforms is that the smoke zones operate by exhausting smoke while other zones in the platform and in the concourse which is the upper floor of the platform operate by supplying air or stopping any ventilation. This study is conducted to evaluate performance of passengers' evacuation for various smoke control modes in the subway station. Distribution of smoke and heat due to fire on the platform is analyzed by using Fire Dynamics Simulator(FDS V 4.06) of NIST. Various smoke-control ventilation modes and locations of fire are considered. Evacuation and movement of passengers within the platform is simulated by building EXODUS V.4.0.
HERMITE BICUBIC STREAM FUNCTION METHOD FOR INCOMPRESSIBLE FLOW COMPUTATIONS IN TWO DIMENSIONS
Kim, J.W. ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 13~23
This paper is an extension of previous study on a development of a divergence-free element method using a hermite interpolated stream function. Divergence-free velocity bases defined on rectangles derived herein produce pointwise divergence-free flow fields. Hence the explicit imposition of continuity constraint is not necessary and the Galerkin finite element formulation for velocities does not involve the pressure. The divergence-free element of the previous study employed hermite (serendipity) cubic for interpolation of stream function, and it has been noted a possible discontinuity in variables along element interfaces. This deficiency can be removed by use of a hermite bicubic interpolated stream function, which requires four degrees-of-freedom at each element corners. Those degrees-of-freedom are the unknown variable, its x- and y-derivatives and its cross derivative. Detailed derivations are presented for both solenoidal and irrotational basis functions from the hermite bicubic interpolated stream function. Numerical tests are performed on the lid-driven cavity flow, and results are compared with those from hermite serendipity cubics and a stabilized finite element method by Illinca et al.
STUDY ON PREDICTION OF THE INDUCED TEMPERATURE IN ENVIRONMENTAL TEST
Lee, J.Y. ; Baek, S.H. ; Park, S.J. ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 24~32
Environmental test is divided into operation test and storage test. The temperature of storage test is induced temperature which is considered with all sort of the heat source. Induced temperature is the temperature to be adapted to each item and platform and can be induced by computer simulation, laboratory, and real field test. We considered the induced temperature to be associated with solar heat source. In this research. First, we compared the induced temperature which be occurred by one experiment for thin plate in solar test chamber with the other one which be occurred by computer simulation to be SolidWorks 2007 COSMOS FloWorks. After this verification, we showed induced temperature which can be occurred when the test item is stored. Especially, we bring out the induced temperature by applying the ambient temperatures which is presented by MIL-STD-810F and brought out in preceding research.
BLOCKAGE EFFECT ON FLOWS AROUND A ROTATIONALLY OSCILLATING CIRCULAR CYLINDER
Kang, Seung-Hee ; Kwon, Oh-Joon ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 33~38
For study on the unsteady blockage effect, flows around a rotationally oscillating circular cylinder with relatively low forcing frequency in closed test-section wind tunnels have been numerically investigated by solving compressible Navier-Stokes equations. The numerical scheme is based on a node-based finite-volume method with the Roe's flux-difference splitting and an implicit time-integration method coupled with dual time-step sub-iteration. The computed results of the oscillating cylinder in the test section showed that the fluctuations of lift and drag are augmented by the blockage effects. The drag further increases because of low base pressure. The pressure on the test section wall shows the harmonics having the oscillating and the shedding frequencies contained in the blockage effect.
CHARACTERISTICS OF UNSTEADY PLANAR-SYMMETRIC AND ASYMMETRIC FLOWS OVER A SPHERE
Kim, Dong-Joo ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 39~44
Numerical simulations of laminar flow over a sphere are conducted to investigate the effect of the Reynolds number on the characteristics of vortex shedding. The Reynolds numbers considered are between 300 and 475, covering unsteady planar-symmetric and asymmetric flows. Results show that the unsteady planar-symmetric flow can be categorized into two different regimes: single-frequency regime and multiple-frequency regime. The former has a single frequency component due to periodic shedding of the vortices with the same strength in every shedding cycle, while the latter has multiple frequency components due to cycle-to-cycle variation in the strength of shed vortices with the shedding angle fixed. The multiple-frequency planar-symmetric flow, which is newly found in the present study, occurs at Re=330
360 between the single-frequency planar-symmetric flow and the asymmetric flow. On the other hand, the asymmetric flow occurs at Re
365, where the vortices shed from the sphere show variation both in strength and shedding angle unlike the planar-symmetric flow. Also, it is shown that the breaking of planar symmetry is closely related to the imbalance of vortical strength between a pair of streamwise vortices.
PERFORMANCE ANALYSIS OF HOVERING UH-60A ROTOR BLADE
Park, Y.M. ; Choi, I.H. ; Chang, B.H. ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 45~49
The present paper describes the results of performance analysis for UH-60A rotor blade in hover. For the numerical simulations, commercial CFD software, FLUENT was used with Spalart-Allmaras turbulence model. The flow solver was based on node based scheme and second order spatial accuracy options was used for simulations. For the enhancement of wake capturing capability, high resolution grid was used around tip vortex region. Granting that somewhat over-prediction of thrust was observed near blade tip region, performance was well correlated with experimental data within 3% accuracy in the operating region. Finally it was shown that the present flow solver can be used as a preliminary performance analysis tool for hovering helicopter rotor blades.
NUMERICAL ANALYSIS OF NON-EQUILIBRIUM HYDRATE PELLET DECOMPOSITION
Kang, Jung-Ho ; Nam, Jin-Hyun ; Kim, Charn-Jung ; Song, Myung-Ho ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 50~57
The prediction of hydrate pellet decomposition characteristics is required to design the regasification process of GTS (gas to solid) technology, which is considered as an economic alternative for LNG technology to transport natural gas produced from small and stranded gas wells. Mathematical model based on the conservation principles, the phase equilibrium relation, equation of gas state and phase change kinetics was set up and numerical solution procedure employing volume averaged fixed grid formulation and extended enthalpy method are implemented. Initially, porous methane hydrate pellet is at uniform temperature and pressure within hydrate stable region. The pressure starts to decrease with a fixed rate down to the final pressure and is kept constant afterwards while the bounding surface of pellet is heated by convection. The predicted convective heat and mass transfer accompanied by the decomposed gas flow through hydrate/ice solid matrix is reported focused on the comparison of spherical and cylindrical pellets having the same effective radius.
A NUMERICAL ANALYSIS ON ELECTROHYDRODYNAMICS (EHD) OF THE FLOW AND THE COLLECTION MECHANISMS INSIDE AN ELECTROSTATIC PRECIPITATOR WITH A SPIRAL SPIKE ELECTRODE
Lee, Sang-Hyuk ; Hur, Nahm-Keon ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 58~65
In the present study, a numerical analysis on electrohydrodynamics (EHD) of the flow and the collection mechanisms inside a electrostatic precipitator with a spiral spike electrode were investigated. The phenomena of the electrostatic precipitator include complex interactions between the electric field, the fluid flow and the particle motion. To validate the numerical method, the numerical computation for the electric field of a simple wire-pipe type electrostatic system having an analytic solution were performed. Using this numerical method, the electric field of the spiked electrostatic precipitator was simulated. And the fluid flow and the particle motion inside the spiked electrostatic precipitator were numerically analyzed.
NUMERICAL AERODYNAMIC ANALYSIS OF A TRANSONIC COMMERCIAL AIRPLANE ACCORDING TO THE ANGLE OF ATTACK AND MACH NUMBER
Kim, Y.K. ; Kim, S.C. ; Choi, J.W. ; Kim, J.S. ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 66~71
This research computes the viscous flow field and aerodynamics around the model of a commercial passenger airplane, Boeing 747-400, which cruises in transonic speed. The configuration was realized through the reverse engineering based on the photo scanning measurement. In results, the pressure coefficients at the several wing section on the wing surface of the airplane was described and discussed to obtain the physical meaning. The lift coefficient increased almost linearly up to
. Here the maximum lift occurred at
according to the angle of attack. And the minimum drag is expected at
. The maximum lift coefficient occurred at the Mach number 0.89, and the drag coefficient rapidly increased after the Mach number of 0.92. Also shear-stress transport model predicts slightly lower aerodynamic coefficients than other models and Chen's model shows the highest aerodynamic values. The aerodynamic performance of the airplane elements was presented.
PERFORMANCE IMPROVEMENT OF A RANGE HOOD SIROCCO FAN BY CFD FLOW ANALYSIS
Han, B.Y. ; Park, J.W. ; Lee, M.S. ; Park, H.K. ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 72~79
This study is to investigate the air flow around a sirocco fan which is used in a range hood. The main object of the study is to improve the flow rate of the fan by analysis of unsteady 3-dimensional incompressible flow. Overall analysis is carried out using CFD method. For this, we used a commercial code, SC/Tetra, and used a sliding mesh method to give the same condition as an actual state. First, verification of the CFD results is done by comparing the experimental data with the numerical data for the suction flow rate. It is confirmed that two results are well consistent. Then for the improvent of flow rate, the effect of shape factors such as diameter ratio of fan, geometry of case, cut-off aperture and guide angle of case exit on the suction flow rate was considered. Especially, for a new design of housing, the principle of Archimedes spiral was used. The overall analysis was applied to a new design of housing, and the result showed an increase of flow rate by 10.7%.
NUMERICAL STUDY OF AN EXTERNAL STORE RELEASED FROM A FIGHTER AIRCRAFT
Yoon, Young-Hyun ; Cho, Hwan-Kee ; Chung, H.S. ; Lee, S.H. ; Han, C.H. ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 80~85
The prediction of the separation trajectories of external stores released from a military aircraft is an important task in the aircraft design area having the objective to define the operational and release envelopes. This paper presents the results obtained for store separation by employing commercial softwares, FLUENT and CFD-FASTRAN. FLUENT treats the rigid body motion by employing a remeshing scheme. CFD-FASTRAN uses Chimera(overset) grid and interpolations. It was found that, for the prediction of the trajectories and behavior of the stores separated from the wing, both codes show the good agreement with the experimental results.
NUMERICAL METHOD FOR TWO-PHASE FLOW ANALYSIS USING SIMPLE-ALGORITHM ON AN UNSTRUCTURED MESH
Kim, Jong-Tae ; Park, Ik-Kyu ; Cho, Hyung-Kyu ; Kim, Kyung Doo ; Jeong, Jae-Jun ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 86~95
For analyses of multi-phase flows in a water-cooled nuclear power plant, a three-dimensional SIMPLE-algorithm based hydrodynamic solver CUPID-S has been developed. As governing equations, it adopts a two-fluid three-field model for the two-phase flows. The three fields represent a continuous liquid, a dispersed droplets, and a vapour field. The governing equations are discretized by a finite volume method on an unstructured grid to handle the geometrical complexity of the nuclear reactors. The phasic momentum equations are coupled and solved with a sparse block Gauss-Seidel matrix solver to increase a numerical stability. The pressure correction equation derived by summing the phasic volume fraction equations is applied on the unstructured mesh in the context of a cell-centered co-located scheme. This paper presents the numerical method and the preliminary results of the calculations.
THEORETICAL STUDIES ON FRICTION DRAG REDUCTION CONTROL WITH THE AID OF DIRECT NUMERICAL SIMULATION - A REVIEW
Fukagata, Koji ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 96~106
We review a series of studies on turbulent skin friction drag reduction in wall-turbulence recently conducted in Japan. First, an identity equation relating the skin friction drag and the Reynolds shearstress (the FIK identity) is introduced. Based on the implication of the FIK identity, a new analytical suboptimal feedback control law requiring the streamwise wall-shear stress only is introduced and direct numerical simulation (DNS) results of turbulent pipe flow with that control is reported. We also introduce DNS of an anisotropic compliant surface and parameter optimization using an evolutionary optimization technique.
NUMERICAL SIMULATION OF FLOW AND HEAT TRANSFER IN A COOLING CHANNEL WITH STAGGERED V-SHAPED RIBS
Myong, H.K. ; Kim, K.Y. ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 107~113
The present study numerically simulates the flow and heat transfer characteristics of rib-induced secondary flow in a square cooling channel with staggered V-shaped ribs, extruded on both walls. The rib pitch-to-height ratio (p/h) varies from 2.8 to 10 with the rib-height-to-hydraulic diameter ration (h/
)of 0.07 and the Reynolds number of 50,000. Shear stress transport (SST) turbulence model is used as a turbulence model. Computational results show that complex secondary flow patterns are generated in the channel due to the snaking flow in the streamwise direction for all tested cases. In the range of p/h=5 to 10 the staggered V-shaped rib gives about 3 times higher heat transfer augmentation than the reference smooth pipe with high heat transfer on both front side and the area around the leading edge of the ribs, while the former cases give about 18 times higher streamwise pressure drop than the latter ones. However, for the thermal performances, based on the equal pumping power condition, the case of p/h=2.8 gives the best result among three cases, mainly due to relatively low streamwise pressure drop, although it gives relatively low heat transfer augmentation.
HUGE DIRECT NUMERICAL SIMULATION OF TURBULENT COMBUSTION - TOWARD PERFECT SIMULATION OF IC ENGINE -
Tanahashi, Mamoru ; Seo, Takehiko ; Sato, Makoto ; Tsunemi, Akihiko ; Miyauchi, Toshio ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 114~125
Current state and perspective of DNS of turbulence and turbulent combustion are discussed with feature trend of the fastest supercomputer in the world. Based on the perspective of DNS of turbulent combustion, possibility of perfect simulations of IC engine is shown. In 2020, the perfect simulation will be realized with 30 billion grid points by 1EXAFlops supercomputer, which requires 4 months CPU time. The CPU time will be reduced to about 4 days if several developments were achieved in the current fundamental researches. To shorten CPU time required for DNS of turbulent combustion, two numerical methods are introduced to full-explicit full-compressible DNS code. One is compact finite difference filter to reduce spatial resolution requirements and numerical oscillations in small scales, and another is well-known point-implicit scheme to avoid quite small time integration of the order of nanosecond for fully explicit DNS. Availability and accuracy of these numerical methods have been confirmed carefully for auto-ignition, planar laminar flame and turbulent premixed flames. To realize DNS of IC engine with realistic kinetic mechanism, several DNS of elemental combustion process in IC engines has been conducted.
A THREE DIMENSIONAL LEVEL SET METHOD FOR TWO PHASE FLOWS
Kang, D.J. ; Ivanova, Ivelina Ivanova ;
Journal of computational fluids engineering, volume 13, issue 4, 2008, Pages 126~134
We developed a three dimensional Navier-Stokes code based on the level set method to simulate two phase flows with high density ratio. The Navier-Stokes equations with consideration of the surface tension effects are solved by using SIMPLE algorithm on a non-staggered grid. The present code is validated by simulating two test problems. First one is to simulate a rising bubble inside a cube. The thickness of the interface of the bubble is shown to affect the pressure distribution around the interface. As the thickness decreases, the pressure field around the interface becomes more oscillatory. As the bubble rises, a ring vortex is shown to form around the interface and the bubble eventually develops into an ellipsoidal shape. Merge of two bubbles inside a container is secondly tested to show the robustness of the present code for two phase flow simulation. Numerical results show stable and reliable behavior during the process of merging of two bubbles. The velocity and pressure fields around the interface of bubbles are shown oscillation free during the merging of two bubbles.