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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 18, Issue 4 - Dec 2013
Volume 18, Issue 3 - Sep 2013
Volume 18, Issue 2 - Jun 2013
Volume 18, Issue 1 - Mar 2013
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ANALYSIS OF UNSTEADY OSCILLATING FLOW AROUND TWO DIMENSIONAL AIRFOIL AT HIGH ANGLE OF ATTACK
Yoo, J.K. ; Kim, J.S. ;
Journal of computational fluids engineering, volume 18, issue 1, 2013, Pages 1~6
DOI : 10.6112/kscfe.2013.18.1.001
Missile and fighter aircraft have been challenged by low restoring nose-down pitching moment at high angle of attach. The consequence of weak nose-down pitching moment can be resulting in a deep stall condition. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance and safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed at high angle of attack up to 50 degrees around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.3 and Reynolds number of
. The lift, drag, pressure, entropy distribution, etc. are analyzed according to the angle of attack. The results of average lift coefficients are compared with other results according to the angle of attack. From a certain high angle of attack, the strong vortex formed by the leading edge are flowing downstream as like Karman vortex around a circular cylinder. The primary and secondary oscillating frequencies are analyzed by the effects of these unsteady aerodynamic characteristics.
NUMERICAL STUDY OF NON-UNIFORM TIP CLEARANCE EFFECTS ON THE PERFORMANCE AND FLOW FIELD IN A CENTRIFUGAL COMPRESSOR
Jung, Y.H. ; Park, J.Y. ; Choi, M. ; Baek, J.H. ;
Journal of computational fluids engineering, volume 18, issue 1, 2013, Pages 7~12
DOI : 10.6112/kscfe.2013.18.1.007
This paper presents a numerical investigation of the influences of various non-uniform tip clearances on the performance and flow field in a centrifugal compressor. Numerical simulations were conducted for three centrifugal compressor impellers in which the tip clearance height varied linearly from the leading edge to the trailing edge. The numerical result was compared with the experimental data for validation. Although the performance improved for low tip clearances, a smaller tip clearance at the trailing edge reduced the overall tip leakage flow more effectively than a smaller tip clearance at the leading edge. Therefore, a smaller tip clearance at the trailing edge lowered the mixing loss caused by interactions between the tip leakage flow and the main passage flow.
NUMERICAL ANALYSIS OF VENTILATED CAVITATION WITH FREE SURFACE EFFECTS
Jin, M.S. ; Kim, H.Y. ; Ha, C.T. ; Park, W.G. ;
Journal of computational fluids engineering, volume 18, issue 1, 2013, Pages 13~21
DOI : 10.6112/kscfe.2013.18.1.013
Cavitating flow is usually formed on the surface of a high speed underwater object. When a object moves near a free surface at very high speed, the cavity signature becomes one of the major factors to be overcome by sensors of military satellite. The present work was to study the free surface effect on the ventilated cavitation. The governing equations were Navier-Stokes equations based on a homogeneous mixture model. The multiphase flow solver used an implicit preconditioning method in the curvilinear coordinate system. The cavitation model used here was the one first presented by Merkle et al.(2006) and redeveloped by Park & Ha(2009). Computations considered the free surface effects were carried out with a NACA0012 hydrofoil and the corresponding results were compared with the experimental data to have a good agreement. Calculations were then performed considering the ventilated cavitation, including the effect of non-condensable gas under the free surface effects.
TWO-DIMENSIONAL COMPUTATIONAL AEROACOUSTICS SIMULATION OF SOUND GENERATED BY FLOW AROUND A CIRCULAR CYLINDER
Park, I.C. ; Go, Y.J. ; Choi, J.S. ; Kim, B.S. ;
Journal of computational fluids engineering, volume 18, issue 1, 2013, Pages 22~27
DOI : 10.6112/kscfe.2013.18.1.022
Researches in the area of aeroacoustics have been conducted by two methods. In the first method theoretical formula or experimentation are utilized, and in the second method flow field analysis and acoustic analogy are utilized. In contrast to the first method, the second method does not need new experiments for every individual change of flow configurations and conditions, and it can predict their effects by the flow field analysis, which makes the second method preferred than the first one. In this paper numerical analysis to predict noise generated by a turbulent flow about a two dimensional circular cylinder by use of CAA (Computational Aeroacoustics) method is conducted and the results are compared to the available experimental data.
EXPERIMENTAL REPRODUCTION AND NUMERICAL ANALYSIS OF THE SIDE FORCE ON AN OGIVE FOREBODY AT A HIGH ANGLE OF ATTACK
Lee, E.S. ; Lee, J.I. ; Lee, K.S. ;
Journal of computational fluids engineering, volume 18, issue 1, 2013, Pages 28~35
DOI : 10.6112/kscfe.2013.18.1.028
Behavior of the side force generated at high angles of attack by two ogive-cylinder bodies of revolution with nose fineness ratio of 2.3 (B1) and 3.5 (B2) and the effect of a strip placed close the nose tip of each body (B1S and B2S) are analyzed through the wind tunnel test at ReD=200,000 and a=42~60 deg. The side force generated by B1 is increased by placing a strip. The side force generated by B2 is in the starboard direction and its magnitude is higher than that of the B1S. The effect of the strips with various dimensions placed on B2 is investigated. It is found that the 4-layer strip placed on the starboard reversed the direction of the side force into port direction. It is confirmed by numerical simulations that the strip promotes the flow separation and increases the average pressure on the side where it is placed and consequently produces the side force in the corresponding direction.
NUMERICAL ANALYSIS FOR SUPPRESSING UNSTEADY WAKE FLOW ON WIND TURBINE TOWER USING EDISON_CFD
Kim, S.Y. ; Jin, D.H. ; Lee, K.B. ; Kim, C. ;
Journal of computational fluids engineering, volume 18, issue 1, 2013, Pages 36~42
DOI : 10.6112/kscfe.2013.18.1.036
The performance of the wind turbine is determined by wind speed and unsteady flow characteristics. Unsteady wake flow causes not only the decline in performance but also structural problems of the wind turbine. In this paper, conceptual designs for the wind turbine tower are conducted to minimize unsteady wake flow. Numerical simulations are performed to inspect the shape effect of the tower. Through the installation of additional structures at the rear of the tower, the creation of Karman vortex is delayed properly and vortex interactions are reduced extremely, which enhance the stability of the wind turbine. From the comparative analysis of lift and drag coefficients for each structure, it is concluded that two streamwise tips with a splitter plate have the most improved aerodynamic characteristics in stabilizing wake flow.
NUMERICAL SIMULATION ON CONTROL OF ENVIRONMENTAL VARIABLES FOR ENVIRONMENT REPRODUCTION SYSTEM USING OPENFOAM
Jeong, S.M. ; Kagemoto, Hiroshi ; Park, J.C. ;
Journal of computational fluids engineering, volume 18, issue 1, 2013, Pages 43~48
DOI : 10.6112/kscfe.2013.18.1.043
The feasibility of a unique greenhouse, named as Gradient Biome, is now being examined extensively in the University of Tokyo. It is a large chamber (length:200m, width:50m, height:40m) in which the weather, such as temperature and humidity, of the tropical zone through to that of the frigid zone on the earth is reproduced with continuous gradient. In the Gradient Biome, ecosystems (mainly plants) corresponding to each weather are introduced and the possible responses of this ecosystems to the expected global warming are to be observed. Since 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 Biome. This requirement is not so easy to be satisfied since the environment tends to be homogeneous. This paper presents the results of the numerical studies conducted to find the ways of how the temperature and humidity in the Gradient Biome could be reproduced. One of the contributed solvers of OpenFOAM, which is an open source physics simulation code, was modified and used for the numerical simulations.
APPLICATION OF AN IMMERSED BOUNDARY METHOD TO SIMULATING FLOW AROUND TWO NEIGHBORING UNDERWATER VEHICLES IN PROXIMITY
Lee, K. ; Yang, K.S. ;
Journal of computational fluids engineering, volume 18, issue 1, 2013, Pages 49~57
DOI : 10.6112/kscfe.2013.18.1.049
Analysis of fluid-structure interaction for two nearby underwater vehicles immersed in the sea is quite challenging because simulation of flow around them is very difficult due to the complexity of underwater vehicle shapes. The conventional approach using body-fitted or unstructured grids demands much time in dynamic grid generation, and yields slow convergence of solution. Since an analysis of fluid-structure interaction must be based on accurate simulation results, a more efficient way of simulating flow around underwater vehicles, without sacrificing accuracy, is desirable. An immersed boundary method facilitates implementation of complicated underwater-vehicle shapes on a Cartesian grid system. An LES modeling is also incorporated to resolve turbulent eddies. In this paper, we will demonstrate the effectiveness of the immersed boundary method we adopted, by presenting the simulation results on the flow around a modeled high-speed underwater vehicle interacting with a modeled low-speed one.
STUDY ON THE PREVENTION METHOD FOR HEAT ACCUMULATION FOR PERSONAL RAPID TRANSIT (PRT) VEHICLE UNDER BODY
Kwon, S.B. ; Song, J.H. ; Kang, S.W. ; Jeong, R.G. ; Kim, H.B. ; Lee, C.H. ; Seo, D.K. ;
Journal of computational fluids engineering, volume 18, issue 1, 2013, Pages 58~62
DOI : 10.6112/kscfe.2013.18.1.058
Personal Rapid Transit (PRT) is the emerging personal transport vehicle operating on the loop automatically. The PRT system utilize the electrical power from super capacity or battery, it is important to manage the power or energy. In this regards, the management of high temperature occurred by the operation of system is significantly important to prevent from serious damage of component. In this study, we studied the adequate shape of underbody which can reduce the heat accumulation by pickup coil and condenser using natural air cooling. We suggested the additional air pathway, air inlet and flow separator to decrease the temperature of the heat source components. It was found that suggested system can decrease the temperature of PRT under body by 16% during the static mode and by 10% during the running mode at 30km/h. It is expected that the findings of this study will feed into final design of newly built Korean PRT vehicle.
THE EFFECTS OF RADIAL HEAT SINK GEOMETRY AND SURFACE COATINGS ON THE LED COOLING PERFORMANCE FOR HIGH POWER LED LAMP
Kim, H.S. ; Park, S.H. ; Kim, D. ; Kim, K. ;
Journal of computational fluids engineering, volume 18, issue 1, 2013, Pages 63~68
DOI : 10.6112/kscfe.2013.18.1.063
The purpose of this study is to investigate the cooling performance of radial heat sink used for high power LED lightings by natural convection cooling with surrounding air. Experimental and numerical analyses are carried out together. Parametric studies are performed to compare the effects of geometric parameters in radial heat sink such as the number of fins, fin height, fin length, and thickness of fin base as well as the surface coatings of radial heat sink. In this study, the cooling of 60 W LED lamp is examined with radiative heat transfer considered as well as natural convection. Numerical results show the optimum condition when the number of fin is 40, heat sink height is 120 mm, fin length is 15 mm, and fin base thickness is 3 mm. The difference in temperature of the LED metal PCB is within
between numerical analyses and experimental results. Also, the CNT coating on the heat sink surface is found to increase the cooling performance significantly.
ANALYSIS ON THE COMPOSITION EFFECT OF FOREST FOR DAMAGE PREVENTION USING CFD
Park, T.W. ; Chang, S.M. ; Kim, S.Y. ; Lee, Y.J. ; Yoon, H.J. ;
Journal of computational fluids engineering, volume 18, issue 1, 2013, Pages 69~76
DOI : 10.6112/kscfe.2013.18.1.069
To reduce the damage from the coastal disaster such as typhoon and tsunami, a possible option is the eco-friendly approach to minimize the destruction of ecological system. One of feasible idea is the forest for damage prevention artificially arranged along the beach. To understand a precise physics on the flow before and after the forest, we use a CFD method. In this paper, a three-dimensional numerical model has been constructed based on tree cases in a real forest located at Byin-myeon, Seocheon-gun, Chungnam. The CFD computation using a commercial code COMSOL multiphysics is performed for the distribution of real spatial coordinate of each tree. Through this investigation, the CFD techniques are shown to be applied to the research of forest composition plan. The physics in the regime from laminar to turbulent flow is qualitatively explained, and the obtained data are compared one another quantitatively.
NUMERICAL ANALYSIS OF CONJUGATE HEAT TRANSFER INSIDE A THERMAL BOUNDARY LAYER CONSIDERING THE EFFECTS OF A FREE STREAM VELOCITY AND A THERMOCOUPLE POSITION
Jeon, B.J. ; Lee, J.A. ; Choi, H.G. ;
Journal of computational fluids engineering, volume 18, issue 1, 2013, Pages 77~82
DOI : 10.6112/kscfe.2013.18.1.077
The error in measuring temperature profiles by thermocouple inside boundary layer mostly comes from the conduction heat transfer of the thermocouple. The error is not negligible when the conductivity of the thermocouple is very high. In this study, the effect of conduction heat transfer of the thermocouple on the temperature profile inside boundary layer was examined by considering both free-stream velocity and a thermocouple position. The conduction error of an E-type thermocouple was investigated by numerical analysis of three-dimensional conjugate heat transfer for various velocity profiles of boundary layer and thermocouple positions.
OPENMP PARALLEL PERFORMANCE OF A CFD CODE ON MULTI-CORE SYSTEMS
Kim, J.K. ; Jang, K.J. ; Kim, T.Y. ; Cho, D.R. ; Kim, S.D. ; Choi, J.Y. ;
Journal of computational fluids engineering, volume 18, issue 1, 2013, Pages 83~90
DOI : 10.6112/kscfe.2013.18.1.083
OpenMP is becoming more and more useful as a simple parallel processing paradigm on SMP (Shared Memory Multi-Processors) computing environment with the development of multi-core processors. However, very few data is available publically regarding the OpenMP performance in CFD (Computational Fluid Dynamics). In the present study a CFD test suite is prepared for the performance evaluation of OpenMP on various multi-core systems. The test suite is composed of two-dimensional numerical simulations for inviscid/viscous and reacting/non-reacting flows using three different levels of grid systems. One to five test runs were carried out on various systems from dual-core dual threads to 16-core 32-threads systems by changing the number of threads engaged for each test up to 80. The results exhibit some interesting results and the lessons learned from the tests would be quite helpful for the further use of OpenMP for CFD studies using multi-core processor systems.
PREDICTION OF AERODYNAMIC PERFORMANCE LOSS OF A WIND TURBINE BLADE SECTION DUE TO CONTAMINANT ACCUMULATION
Yang, T.H. ; Choi, J.H. ; Yu, D.O. ; Kwon, O.J. ;
Journal of computational fluids engineering, volume 18, issue 1, 2013, Pages 91~97
DOI : 10.6112/kscfe.2013.18.1.091
In the present study, the effects of contaminant accumulation and surface roughness on the aerodynamic performance of wind turbine blade sections were numerically investigated by using a flow solver based on unstructured meshes. The turbulent flow over the rough surface was modeled by a modified
SST turbulence model. The calculations were made for the NREL S809 airfoil with varying contaminant sizes and positions at several angles of attack. It was found that as the contaminant size increases, the degradation of the airfoil performance becomes more significant, and this trend is further amplified near the stall condition. When the contaminant is located at the upper surface near the leading edge, the loss in the aerodynamic performance of the blade section becomes more critical. It was also found that the surface roughness leads to a significant reduction of lift, in addition to increased drag.