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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 21, Issue 3 - Sep 2016
Volume 21, Issue 2 - Jun 2016
Volume 21, Issue 1 - Mar 2016
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PERFORMANCE OF LIMITERS IN MODAL DISCONTINUOUS GALERKIN METHODS FOR 1-D EULER EQUATIONS
Karchani, A. ; Myong, R.S. ;
Journal of computational fluids engineering, volume 21, issue 2, 2016, Pages 1~11
DOI : 10.6112/kscfe.2016.21.2.001
Considerable efforts are required to develop a monotone, robust and stable high-order numerical scheme for solving the hyperbolic system. The discontinuous Galerkin(DG) method is a natural choice, but elimination of the spurious oscillations from the high-order solutions demands a new development of proper limiters for the DG method. There are several available limiters for controlling or removing unphysical oscillations from the high-order approximate solution; however, very few studies were directed to analyze the exact role of the limiters in the hyperbolic systems. In this study, the performance of the several well-known limiters is examined by comparing the high-order(
) approximate solutions with the exact solutions. It is shown that the accuracy of the limiter is in general problem-dependent, although the Hermite WENO limiter and maximum principle limiter perform better than the TVD and generalized moment limiters for most of the test cases. It is also shown that application of the troubled cell indicators may improve the accuracy of the limiters under some specific conditions.
A STUDY ON THE IMPROVEMENT OF κ-εTURBULENCE MODEL FOR PREDICTION OF THE RECIRCULATION FLOW
Lee, Y.M. ; Kim, C.W. ;
Journal of computational fluids engineering, volume 21, issue 2, 2016, Pages 12~24
DOI : 10.6112/kscfe.2016.21.2.012
models are adopted to improve the prediction performance on the recirculating flow. In this paper, the backward facing step flows are used to assess the prediction performance of the recirculation zone. The model constants of turbulence model are obtained by the experimental results and they have a different value according to the flow. In the case of an isotropic flow situation, decaying of turbulent kinetic energy should follow a power law behavior. In accordance with the power law, the coefficients for the dissipation rate of turbulent kinetic energy are not universal. Also, the other coefficients as well as the dissipation coefficient are not constant. As a result, a suitable coefficients can be varied according to each of the flow. The changes of flow over the backward facing step in accordance with model constants of the
models show that the reattachment length is dependent on the growth rate(
) and the
models can be improved the prediction performance by changing the model constants about the recirculating flow. In addition, it was investigated for the curvature correction effect of the
models in the recirculating flow. Overall, the curvature corrected
models showed an excellent prediction performance.
DEVELOPMENT OF OPENFOAM GRID GENERATION PROGRAM FOR TWO-DIMENSIONAL FLOW ANALYSIS
Kim, W.H. ; Kim, B.S. ;
Journal of computational fluids engineering, volume 21, issue 2, 2016, Pages 25~31
DOI : 10.6112/kscfe.2016.21.2.025
In this paper, a study on the development of OpenFOAM grid generation program for two-dimensional flow analysis is described. By using the pre-processor(eMEGA) of EDISON_CFD system, grids for OpenFOAM flow calculation were obtained. Resultant two-dimensional grids were used to calculate flow fields by applying simpleFoam, one of the OpenFOAM`s popular solvers, and the obtained flow results were compared with theoretical and experimental data available. Also grids generated by present program were compared with grids by a commercial pre-processor Pointwise for the purpose of verification. Verification work includes three cases(single block, O-type single block, and multi block grid), and all results show reasonable matches. According to the current achievement, it can be concluded that OpenFOAM grid can be constructed conveniently by using eMEGA with GUI.
NUMERICAL SIMULATION ON CONTROL OF HUMIDITY AND AIR TEMPERATURE IN THE GRADIENT BIOME
Jeong, S.M. ;
Journal of computational fluids engineering, volume 21, issue 2, 2016, Pages 32~39
DOI : 10.6112/kscfe.2016.21.2.032
The Gradient Biome is a unique and large greenhouse(length 200 m, width 50 m, height:40 m) in which the elements of the weather, such as temperature and humidity, are controlled and reproduced in such a way as to create a continuous gradient from the tropical to frigid zones along specified longitudinal or transvers lines on the earth. One of the main purposes of the Gradient Biome is to observe the possible responses of the ecosystems (mainly plants), which are to be corresponding to each test climate and be introduced in the Biome, to the expected global warming. As one of the expected responses is the shift of the ecosystem(s) toward the region of suitable environment, there should be no artificial obstacles, which can prevent the shift, inside the facility. However, it is important but not so easy to find the ways of how the temperature and humidity in the Biome could be reproduced since the environmental variables tends to be homogeneous. In this paper, numerical simulations were carried out to find the effective control methods for air temperature and humidity inside the real scale Biome. One of the contributed solvers of OpenFOAM, which is an open source physics simulation code, was modified and used for the simulations.
NUMERICAL STUDY ON THE IMPROVEMENT OF VENTURI FLOWMETER WITH FOULING EFFECT
Kim, W.H. ; Lee, Y.J. ; Yang, J.S. ; Kim, Y.B. ; Kim, B.S. ;
Journal of computational fluids engineering, volume 21, issue 2, 2016, Pages 40~46
DOI : 10.6112/kscfe.2016.21.2.040
In the paper, a study on the analysis of fouling effect of the venturi flowmeter is described. In the research flow field solutions about the venturi flowmeter with fouling are obtained and then the effects on fouling states by inserting a ring into the throat of venturi flowmeter are studied. As the result shows, it is found that the inserted ring reduces the fouling effect due to the flow separation occurring at the ring. Consequently, a venturi flowmeter with ring shows smaller pressure loss differences than the original configuration with no ring on fouling state. This research suggests an efficient and economic method of inserting a ring to reduce the pressure loss effects due to fouling.
ANALYSIS ON FLOW FIELDS IN AIRFLOW PATH OF CONCRETE DRY STORAGE CASK USING FLUENT CODE
Kang, G.U. ; Kim, H.J. ; Cho, C.H. ;
Journal of computational fluids engineering, volume 21, issue 2, 2016, Pages 47~53
DOI : 10.6112/kscfe.2016.21.2.047
This study investigated natural convection flow behavior in airflow path designed in concrete dry storage cask to remove the decay heat from spent nuclear fuels. Using FLUENT 16.1 code, thermal analysis for natural convection was carried out for three dimensional, 1/4 symmetry model under the normal condition that inlet ducts are 100% open. The maximum temperatures on other components except the fuel regions were satisfied with allowable values suggested in nuclear regulation-1536. From velocity and temperature distributions along the flow direction, the flow behavior in horizontal duct of air inlet and outlet duct, annular flow-path and bent pipe was delineated in detail. Theses results will be used as the theoretical background for the composing of airflow path for the designing of passive heat removal system by understanding the flow phenomena in airflow path.
ANALYSIS OF HEAT TRANSFER ON SPENT FUEL DRY CASK DURING SHORT-TERM OPERATIONS
Kim, H. ; Lee, D.G. ; Kang, G.U. ; Cho, C.H. ; Kwon, O.J. ;
Journal of computational fluids engineering, volume 21, issue 2, 2016, Pages 54~61
DOI : 10.6112/kscfe.2016.21.2.054
When spent fuel assemblies from the reactor of nuclear power plants(NPPs) are transported, the assemblies are exposed to short-term operations that can affect the peak cladding temperature of spent fuel assemblies. Therefore, it needs to perform the analysis of heat transfer on spent fuel dry cask during the operation. For 3 dimensional computational fluid dynamnics(CFD) simulation, it is proposed that the short-term operation is divided into three processes: Wet, dry, and vacuum drying condition. The three processes have different heat transfer mode and medium. Metal transportation cask, which is Korea Radioactive Waste Agency(KORAD)`s developing cask, is evaluated by the methods proposed in this work. During working hours, the boiling at wet process does not occur in the cask and the peak cladding temperatures of all processes remain below
. The maximum peak cladding temperature is
at vacuum drying process and the temperature rise of dry, and vacuum drying process occurs steeply.
RANS ANALYSES OF THE TIP VORTEX FLOW OF A MARINE PROPELLER
Park, I.R. ;
Journal of computational fluids engineering, volume 21, issue 2, 2016, Pages 62~69
DOI : 10.6112/kscfe.2016.21.2.062
It has been highly demanded to improve the accuracy of CFD(Computational Fluid Dynamics) methods for the assessment of the hydrodynamic performance of marine propellers in cavitating and non-cavitating flows. This paper presents a validation study on the numerical simulation of the tip vortex flow of a non-cavitating marine propeller SVA VP1304. The calculations are carried out by using the Reynolds averaged Navier-Stokes(RANS) approach, where the Reynolds Stress Model(RSM) is used for turbulence closure. The present paper contains a grid dependence test for the propeller open water simulations and a special emphasis is placed on conducting a local grid adaptation on the blade tip and in the tip vortex to reasonably reproduce the velocity and the pressure in the tip vortex flow field. The numerical results are compared with the experimental validation data, which are published in the second International Symposium on Marine Propulsors 2011(SMP`11). The present numerical results show a reasonable agreement with the experiments.
COMPARISON OF COMMERCIAL AND OPEN SOURCE CFD CODES FOR AERODYNAMIC ANALYSIS OF FLIGHT VEHICLES AT LOW SPEEDS
Park, D.H. ; Kim, C.W. ; Lee, Y.G. ;
Journal of computational fluids engineering, volume 21, issue 2, 2016, Pages 70~80
DOI : 10.6112/kscfe.2016.21.2.070
The comparison of two commercial codes(FLUENT and STAR-CCM+) and an open-source code(OpenFOAM) are carried out for the aerodynamic analysis of flight vehicles at low speeds. Tailless blended-wing-body UCAV, main wing and propeller of HALE UAV(EAV-3) are chosen as geometries for the investigation. Using the same mesh, incompressible flow simulations are carried out and the results from three different codes are compared. In the linear region, the maximum difference of lift and drag coefficients of UCAV are found to be less than 2% and 5 counts, respectively and shows good agreement with wind tunnel test data. In a stall region, however, the reliability of RANS simulation is found to become poor and the uncertainty according to code also increases. The effect of turbulence models and meshes generated from different tools are also examined. The transition model yields better results in terms of drag which are much closer to the test data. The pitching moment is confirmed to be sensitive to the existence and the location of transition. For the case of EAV-3 wing, the difference of results with
SST model is increased when Reynolds number becomes low. The results for the propeller show good agreement within 1% difference of thrust. The reliability and uncertainty of three codes is found to be reasonable for the purpose of engineering use. However, the physical validity and reliability of results seem to be carefully examined when
SST model is used for aerodynamic simulation at low speeds or low Reynolds number conditions.
SIMULATION OF PARTICLE DISPERSION AND DEPOSITION IN FLOW AROUND TWO CIRCULAR CYLINDERS IN A SIDE-BY-SIDE ARRANGEMENT
Hwang, Dongjun ; Kim, Dongjoo ;
Journal of computational fluids engineering, volume 21, issue 2, 2016, Pages 81~89
DOI : 10.6112/kscfe.2016.21.2.081
Numerical simulations are carried out for the fluid flow and particle transport around two nearby circular cylinders in a side-by-side arrangement. The present study aims to understand the effects of the particle Stokes number and the spacing between two cylinders on particle dispersion and deposition characteristics. Simulations are based on an Eulerian-Lagrangian approach where the motion of particles is calculated by a Lagrangian approach based on one-way coupling. Results show that the flow structure is very different depending on the cylinder spacing, eventually affecting the overall pattern of particle dispersion significantly. It is also found that particles with smaller Stokes number tend to be distributed more uniformly in the wake of two cylinders, being located even inside the vortex cores. Meanwhile, particle deposition is analyzed in terms of the deposition efficiency and deposition location. The deposition efficiency of particles strongly depends on the Stokes number, whereas it is slightly affected by the cylinder spacing. The deposition location gets wider as the Stokes number increases, and it becomes asymmetric about the center of each cylinder as the cylinders get close.
A NUMERICAL STUDY ON THERMAL DESIGN OF A LARGE-AREA HOT PLATE FOR THERMAL NANOIMPRINT LITHOGRAPHY
Park, G.J. ; Lee, J.J. ; Kwak, H.S. ;
Journal of computational fluids engineering, volume 21, issue 2, 2016, Pages 90~98
DOI : 10.6112/kscfe.2016.21.2.090
A numerical study is conducted on thermal performance of a large-area hot plate specially designed as a heating and cooling tool for thermal nanoimprint lithography process. The hot plate has a dimension of
, in which a series of cartridge heaters and cooling holes are installed. The material is stainless steel selected for enduring the high molding pressure. A numerical model based on the ANSYS Fluent is employed to predict the thermal behavior of the hot plate both in heating and cooling phases. The PID thermal control of the device is modeled by adding user defined functions. The results of numerical computation demonstrate that the use of cartridge heaters provides sufficient heat-up performance and the active liquid cooling in the cooling holes provides the required cool-down performance. However, a crucial technical issue is raised that the proposed design poses a large temperature non-uniformity in the steady heating phase and in the transient cooling phase. As a remedy, a new hot plate in which heat pipes are installed in the cooling holes is considered. The numerical results show that the installation of heat pipes could enhance the temperature uniformity both in the heating and cooling phases.
NUMERICAL ANALYSIS FOR FLOW CHARACTERISTICS WITH GEOMETRIC SHAPE AND CONTROL CONDITIONS IN SUBSEA BY-PASS VALVE
Lee, J.H. ; Min, C.H. ; Oh, J.W. ; Cho, S. ; Kim, H.W. ;
Journal of computational fluids engineering, volume 21, issue 2, 2016, Pages 99~105
DOI : 10.6112/kscfe.2016.21.2.099
The present study has been carried out to analyze the flow characteristics with geometric shape and control conditions in subsea by-pass valve. The function of by-pass valve is to prevent reverse flow. In this study, the static analysis has been perform for analyzing fluid flow in open state. In order to consider the turbulent effect, the standard
model was used. A variety of parametric studies, such as by-pass valve type or size, volume flow rate, leakage hole size, leakage hole position, block type, block shape, were performed. The pressure difference across the valve in the model broadened the flow channel cross-sectional area was greater than the base model for the same operating conditions. As the pipe diameter in the block decreases the pressure difference is greatly increased. The pressure difference according to block shape such as edge type and round was almost negligible. For the same Reynolds number the pressure difference was little changed according to the size of the valve.
CHANGES IN STAGNATION REGION AND RESIDENCE TIME OF COOLING WATER FOR VARIOUS FLOW CHANNEL GEOMETRY OF WATER COOLING GRATE
Song, D.K. ; Kim, S.B. ; Park, D.W. ;
Journal of computational fluids engineering, volume 21, issue 2, 2016, Pages 106~111
DOI : 10.6112/kscfe.2016.21.2.106
Waste-to-energy facilities including incinerators are known as an efficient method to reduce wastes. In waste-to-energy facilities, more efficient cooling system is still needed for grates as the energy density of waste increased. For better cooling performance with the water-cooled grates, optimal design of cooling water pathways is highly beneficial. We performed numerical investigation on fluid flow and residence time of cooling water with change of the geometry of the cooling water pathway. With addition of round shaped guide vanes in the water pathway, the maximum residence time of flow is reduced(from 4.3 sec. to 2.4 sec.), but there is no significant difference in pressure drop between inlet and outlet, and average residence time at the outlet. Furthermore the flow stagnation region moves to the outlet, as the position of the round shaped guide vanes is located to the neck point of pathways.
MULTI-PHYSICAL SIMULATION FOR THE DESIGN OF AN ELECTRIC RESISTOJET GAS THRUSTER IN THE NEXTSAT-1
Chang, S.M. ; Choi, J.C. ; Han, C.Y. ; Shin, G.H. ;
Journal of computational fluids engineering, volume 21, issue 2, 2016, Pages 112~119
DOI : 10.6112/kscfe.2016.21.2.112
NEXTSat-1 is the next-generation small-size artificial satellite system planed by the Satellite Technology Research Center(SatTReC) in Korea Advanced Institute of Science and Technology(KAIST). For the control of attitude and transition of the orbit, the system has adopted a RHM(Resisto-jet Head Module), which has a very simple geometry with a reasonable efficiency. An axisymmetric model is devised with two coil-resistance heaters using xenon(Xe) gas, and the minimum required specific impulse is 60 seconds under the thrust more than 30 milli-Newton. To design the module, seven basic parameters should be decided: the nozzle shape, the power distribution of heater, the pressure drop of filter, the diameter of nozzle throat, the slant length and the angle of nozzle, and the size of reservoir, etc. After quasi one-dimensional analysis, a theoretical value of specific impulse is calculated, and the optima of parameters are found out from the baseline with a series of multi-physical numerical simulations based on the compressible Navier-Stokes equations for gas and the heat conduction energy equation for solid. A commercial code, COMSOL Multiphysics is used for the computation with a FEM (finite element method) based numerical scheme. The final values of design parameters indicate 5.8% better performance than those of baseline design after the verification with all the tuned parameters. The present method should be effective to reduce the time cost of trial and error in the development of RHM, the thruster of NEXTSat-1.