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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 19, Issue 4 - Dec 2014
Volume 19, Issue 3 - Sep 2014
Volume 19, Issue 2 - Jun 2014
Volume 19, Issue 1 - Mar 2014
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NUMERICAL STUDY OF UNSTEADY HEAT TRANSFER ON MICRO HEATER UNDER HALF-CYCLE SINUSOIDAL HEAT LOAD
Kim, M.J. ; Lee, H.J. ;
Journal of computational fluids engineering, volume 19, issue 4, 2014, Pages 1~7
DOI : 10.6112/kscfe.2014.19.4.001
A numerical study of transient conjugate heat transfer on micro heater in a micro-channel substrate under a sinusoidal heat load was conducted. It was found that the time constant is not affected by the maximum heating magnitude of the sinusoidal heat load. However, the time constant increases with low duration of the sinusoidal heating period and low Reynolds number. Moreover, there is a threshold where a heater temperature do not reach to time constant at low thermal diffusivity, low flow rate, and low pulse duration of the sinusoidal heating. The time constant should be considered for transient convective heat transfer under transient sinusoidal heat load in a micro heat sink.
DESIGN OF HELIX PITCH OF A CYCLONE TYPE OIL SEPARATOR FOR A COMPRESSOR
Jang, Seongil ; Ahn, Joon ;
Journal of computational fluids engineering, volume 19, issue 4, 2014, Pages 8~13
DOI : 10.6112/kscfe.2014.19.4.008
A series of numerical simulation has been carried out to study performance of a cyclone type oil separator, which is designed for the compressor of a refrigeration system. Working fluid is R22, which is a typical refrigerant, and mineral oil droplet is supplied. Pitch of the helix is considered as design parameters to make a compact separator. Depending on the helix pitch, separation efficiency varies from 97.5 to 99%, while predicted pressure drop ranges from 5 to 6.5 kPa. Considering both of the pressure drop and separation efficiency, helix pitch of the separator has been designed as 50 mm.
DESIGN OPTIMIZATION AND PERFORMANCE ANALYSIS OF INTERNAL COOLING PASSAGE WITH VARIOUS TYPE OF RIB TURBULATOR FOR HIGH PRESSURE TURBINE NOZZLE
Lee, S.A. ; Rhee, D.H. ; Kang, Y.S. ; Yee, K.J. ; Kim, K.H. ;
Journal of computational fluids engineering, volume 19, issue 4, 2014, Pages 14~19
DOI : 10.6112/kscfe.2014.19.4.014
This study conducts shape optimization of rib turbulator on the internal cooling passage that has triangular cross-section of high pressure turbine nozzle. During optimization, various types of rib turbulator including angled, V-shaped, A-shaped and angled rib with intersecting rib are considered. Each type of rib turbulator is parameterized with attack angle(s), rib height, spacing ratio and bending/intersecting location. For optimization, Design of Experiment (DOE) and Kriging surrogate model are used to utilize computational resource more efficiently and Genetic Algorithm (GA) is used to search the optimum points. As a result, Pareto front of each type of rib turbulator with friction factor that relates to pressure drop in cooling passage and spatially averaged Nusselt number that relates to heat transfer on the wall is drawn and optimum points on the Pareto front are suggested.
AN EFFICIENT ALGORITHM FOR INCOMPRESSIBLE FREE SURFACE FLOW ON CARTESIAN MESHES
Go, G.S. ; Ahn, H.T. ;
Journal of computational fluids engineering, volume 19, issue 4, 2014, Pages 20~28
DOI : 10.6112/kscfe.2014.19.4.020
An efficient solution algorithm for simulating free surface problem is presented. Navier-Stokes equations for variable density incompressible flow are employed as the governing equation on Cartesian meshes. In order to describe the free surface motion efficiently, VOF(Volume Of Fluid) method utilizing THINC(Tangent of Hyperbola for Interface Capturing) scheme is employed. The most time-consuming part of the current free surface flow simulations is the solution step of the linear system, derived by the pressure Poisson equation. To solve a pressure Poisson equation efficiently, the PCG(Preconditioned Conjugate Gradient) method is utilized. This study showed that the proper application of the preconditioner is the key for the efficient solution of the free surface flow when its pressure Poisson equation is solved by the CG method. To demonstrate the efficiency of the current approach, we compared the convergence histories of different algorithms for solving the pressure Poisson equation.
LARGE EDDY SIMULATION OF THERMAL STRIPING IN THE UPPER PLENUM OF FAST REACTOR
Choi, S.K. ; Han, J.W. ; Kim, D. ; Lee, T.H. ;
Journal of computational fluids engineering, volume 19, issue 4, 2014, Pages 29~36
DOI : 10.6112/kscfe.2014.19.4.029
A computational study of a thermal striping in the upper plenum of PGSFR(Prototype Generation-IV Sodium-cooled Fast Reactor) being developed at the KAERI(Korea Atomic Energy Research Institute) is presented. The LES(Large Eddy Simulation) approach is employed for the simulation of thermal striping in the upper plenum of the PGSFR. The LES is performed using the WALE (Wall-Adapting Local Eddy-viscosity) model. More than 19.7 million unstructured elements are generated in upper plenum region of the PGSFR using the CFX-Mesh commercial code. The time-averaged velocity components and temperature field in the complicated upper plenum of the PGSFR are presented. The time history of temperature fluctuation at the eight locations of solid walls of UIS(Upper Internal Structure) and IHX(Intermediate Heat eXchanger) are additionally stored. It has been confirmed that the most vulnerable regions to thermal striping are the first plate of UIS. From the temporal variation of temperature at the solid walls, it was possible to find the locations where the thermal stress is large and need to assess whether the solid structures can endure the thermal stress during the reactor life time.
A STUDY ON THERMAL MODEL REDUCTION AND DYNAMIC RESPONSE
Jun, Hyoung Yoll ; Kim, Jung-Hoon ;
Journal of computational fluids engineering, volume 19, issue 4, 2014, Pages 37~44
DOI : 10.6112/kscfe.2014.19.4.037
A detailed satellite panel thermal model composed of more than thousands nodes can not be directly integrated into a spacecraft thermal model due to its node size and the limitation of commercial satellite thermal analysis programs. For the integration of the panel into the satellite thermal model, a reduced thermal model having proper accuracy is required. A thermal model reduction method was developed and validated by using a geostationary satellite panel. The temperature differences of main components between the detailed and the reduced thermal model were less than
in steady state analysis. Also, the dynamic responses of the detailed and the reduced thermal model show very similar trends. Thus, the developed reduction method can be applicable to actual satellite thermal design and analysis with resonable accuracy and convenience.
NUMERICAL SIMULATION OF INITIAL FIREBALL AFTER NUCLEAR EXPLOSION
Song, Seungho ; Lee, Changhoon ; Choi, Jung-Il ;
Journal of computational fluids engineering, volume 19, issue 4, 2014, Pages 45~51
DOI : 10.6112/kscfe.2014.19.4.045
We develop a numerical method for solving the radiation hydrodynamic equations in one-dimensional spherical coordinates. The present method is validated through simulations of shock tube, thermal radiative diffusion and point explosion problems. The transient growth of the fireball is investigated by varying explosion yields. The present study clearly captures well-known breakaway phenomena related to the shock separation between pressure waves and thermal shock front. The fireball radius at the breakaway point is roughly increased by the yield to power of 0.4.
NUMERICAL SIMULATION OF TSUNAMI WITH VOF METHOD BASED ON FVM
Myong, Hyon Kook ; Park, Jin Woo ;
Journal of computational fluids engineering, volume 19, issue 4, 2014, Pages 52~60
DOI : 10.6112/kscfe.2014.19.4.052
Recently, coastal structures have been built to protect coastal areas. However, if a tidal wave caused by an earthquake hits the coast, it would cause catastrophic damages. It is important to analyze the basics and the characteristics of a tsunami to reduce damages caused by natural disasters. In this study, a tsunami passing over different topographical changes is simulated with VOF method based on FVM(Finite Volume Method). The reduction of both scale and velocity is accomplished by similarity analysis, and an initial energy is generated by increasing the water level as needed to create a tsunami as if it is caused by a crustal movement. It is found that the present method is appropriate to simulate the tsunami with its mechanism.
NUMERICAL STUDY ON THE CHARACTERISTICS OF NON-NEWTONIAN FLUID FLOW OVER OBSTACLE
Kim, Hyung Min ;
Journal of computational fluids engineering, volume 19, issue 4, 2014, Pages 61~67
DOI : 10.6112/kscfe.2014.19.4.061
Since the most of the existing non-Newtonian models are not adequate to apply to the lattmce Boltzmann method, it is a challenging task from both the theoretical and the numerical points of view. In this research the hydro-kinetic model was modified and applied to the 3-D moving sphere in the circular channel flow and the characteristics of the shear thinning effect by the HK-model was evaluated and the condition of
in the model was suggested for the stable simulation to generate non-trivial prediction in three dimension strong shear flows. On the wall boundaries of circular channel the curved wall surface treatment with constant velocity condition was applied and the bounceback condition was applied on the sphere wall to simulate the relative motion of the sphere. The condition is adequate at the less blockage than 0.7 but It may need to apply a multi-scale concept of grid refinement at the narrow flow region. to obtain the stable numerical results.
COMPUTATIONAL MODELING AND SIMULATION OF METAL PLASMA GENERATION BETWEEN CYLINDRICAL ELECTRODES USING PULSED POWER
Kim, K. ; Kwak, H.S. ; Park, J.Y. ;
Journal of computational fluids engineering, volume 19, issue 4, 2014, Pages 68~74
DOI : 10.6112/kscfe.2014.19.4.068
This computational study features the transient compressible and inviscid flow analysis on a metallic plasma discharge from the opposing composite electrodes which is subjected to pulsed electric power. The computations have been performed using the flux corrected transport algorithm on the axisymmetric two-dimensional domain of electrode gap and outer space along with the calculation of plasma compositions and thermophysical properties such as plasma electrical conductivity. The mass ablation from aluminum electrode surfaces are modeled with radiative flux from plasma column experiencing intense Joule heating. The computational results shows the highly ionized and highly under-expanded supersonic plasma discharge with strong shock structure of Mach disk and blast wave propagation, which is very similar to muzzle blast or axial plasma jet flows. Also, the geometrical effects of composite electrodes are investigated to compare the amount of mass ablation and penetration depth of plasma discharge.
STUDY ON THE EFFECTS OF AIRFOIL TRAILING EDGE SHAPE ON THE WING AERODYNAMICS
Kim, W.H. ; Ryu, G.M. ; Kim, B.S. ;
Journal of computational fluids engineering, volume 19, issue 4, 2014, Pages 75~79
DOI : 10.6112/kscfe.2014.19.4.075
In the paper, a study on the analysis of the effects of trailing edge thickness on the aerodynamic characteristics of an airfoil is described. In this research, modification of the formula representing NACA symmetric airfoil is studied to change the airfoil shape with different trailing edge thickness of user`s choice. According to the result of aerodynamic characteristics, as the trailing edge thickness increases the maximum lift coefficient increases while the lift-to-drag ratio decreases. In this paper flow calculation results are demonstrated and the analysis on those results and findings on the effects of non-zero thickness of trailing edge are suggested.
AN INVESTIGATION ON HVLS FAN PERFORMANCE WITH DIFFERENT BLADE CONFIGURATIONS
Moshfeghi, Mohammad ; Hur, Nahmkeon ; Kim, Young Joo ; Kang, Hyun Wook ;
Journal of computational fluids engineering, volume 19, issue 4, 2014, Pages 80~85
DOI : 10.6112/kscfe.2014.19.4.080
High-volume low-speed (HVLS) fans are one category of ceiling fan installed in large enclosings such as warehouses, large barns and health clubs in order to generate comfortable air circulation. As a rotary blade, aerodynamic performance of a HVLS fan is predominantly related to its airfoil(s), and the pitch and twist angles. This paper first, investigates the effects of airfoil on the performances of three different HVLS fans with NACA 5414, 6413 and 7415 airfoils. The fans have six untwisted blades with the diameter of 6 m and rotate at 60 RPM. The blades pitch angels are
, respectively. The results are presented in the form of the aerodynamic forces and moments, volumetric flow rate and streamlines. Regarding the volumetric flow of air, the results show that the model with NACA 7415 has the best performance. Hence, two other HVLS fans with the same airfoil but, with four and five blades are studied in order to investigate the effects of number of blades. From the point of view of air circulation still the six-bladed fan is the best one; however, the five-bladed fan is more efficient in power consumption.
EFFECT OF THE CHANNEL STRUCTURE ON THE COOLING PERFORMANCE OF RADIATOR FOR TRANSFORMER OF NATURAL CONVECTION TYPE
Kim, D.E. ; Kang, S. ; Suh, Y.K. ;
Journal of computational fluids engineering, volume 19, issue 4, 2014, Pages 86~93
DOI : 10.6112/kscfe.2014.19.4.086
Increased demand of power-transformer`s capacity inevitably results in an excessive temperature rise of transformer components, which in turn requires improved radiator design. In this paper, numerical simulation of the cooling performance of an ONAN-type (Oil Natural Air Natural) radiator surrounded by air was performed by using CFX. The natural convection of the air was treated with the full-model. The present parametric study considers variation of important variables that are expected to affect the cooling performance. We changed the pattern and cross-sectional area of flow passages, the fin interval, the flow rate of oil and shape of flow passages. Results show that the area of flow passage, the fin interval, the flow rate of oil and shape of flow passages considerably affect the cooling performance whereas the pattern of flow passages is not so much influential. We also found that for the case of the fin interval smaller than the basic design, the temperature drop decreases while a larger interval gives almost unchanged temperature drop, indicating that the basic design is optimal. Further, as the flow rate of oil increases, the temperature drop slowly decreases as expected. On the other hand, when the shape of flow passages are changed, temperature drop is increased, indicating that the cooling performance is enhanced thereupon.
AERODYNAMIC CHARACTERISTICS OF NACA64-418 AIRFOIL WITH BLUNT TRAILING EDGE ACCORDING TO THE SHAPE OF TRAILING EDGE
Yoo, H.S. ; Lee, J.C. ;
Journal of computational fluids engineering, volume 19, issue 4, 2014, Pages 94~99
DOI : 10.6112/kscfe.2014.19.4.094
The aerodynamic performance of a modified NACA64-418 with blunt trailing edges of irregular shape was investigated. As the trailing edge of the airfoil was thickened, the drag of the airfoil was increased due to development of a re-circulation bubble in the wake region. To reduce the drag of the airfoil with a blunt trailing edge, the optimum shape of the trailing edge for a modified NACA64-418 was investigated. The numerical results showed that the drag of the protruding shape was much more decreased than that of the retreating shape, but the lift was almost the same regardless of shape. In addition, the pitching moment of the modified NACA64-418 with a protruding sharp trailing edge was the smallest at the given angle of attack.