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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 17, Issue 4 - Dec 2012
Volume 17, Issue 3 - Sep 2012
Volume 17, Issue 2 - Jun 2012
Volume 17, Issue 1 - Mar 2012
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FLOW CHARACTERISTICS OF A SYSTEM WHICH HAS TWO PARALLEL PUMPS
Park, J.G. ; Park, J.H. ; Park, Y.C. ;
Journal of computational fluids engineering, volume 17, issue 4, 2012, Pages 1~8
DOI : 10.6112/kscfe.2012.17.4.001
During a reactor normal operation, two parallel 50% capacity cooling pumps circulate primary coolant to remove the fission reaction heat of the reactor through heat exchangers cold by a cooling tower. When one pump is failure, the other pump shall continuously circulate the coolant to remove the residual heat generated by the fuels loaded in the reactor after reactor shutdown. It is necessary to estimate how much flow rate will be supplied to remove the residual heat. We carried out a flow network analysis for the parallel primary pumps based on the piping network of the primary cooling system in HANARO. As result, it is estimated that the flow rate of one pump increased about 1.33 times the rated flow of one pump and was maintained within the limit of the cavitation critical flow.
A STUDY ON THERMAL MODEL REDUCTION ALGORITHM FOR SATELLITE PANEL
Kim, Jung-Hoon ; Jun, Hyoung Yoll ; Kim, Seung Jo ;
Journal of computational fluids engineering, volume 17, issue 4, 2012, Pages 9~15
DOI : 10.6112/kscfe.2012.17.4.009
Thermal model reduction algorithms and techniques are introduced to condense a huge satellite panel thermal model into the simplified model on the purpose of calculating the thermal responses of a satellite on orbit. Guyan condensation algorithm with the substitution matrix manipulation is developed and the mathematical procedure is depicted step by step. A block-form LU decomposition method is also invited to compare the developed algorithm. The constructed reduced thermal model induced from the detailed model based on a real satellite panel is satisfying the correlation criterion of
for the validity accuracy. Guyan condensation algorithm is superior to the block-form LU decomposition method on computation time.
HEAT-TREATMENT OF LARGE-SCALE GLASS BACKPLANES IN A MUFFLE FURNACE
Kim, D.H. ; Son, G. ; Hur, N. ; Kim, B.K. ; Kim, H.J. ; Park, S.H. ;
Journal of computational fluids engineering, volume 17, issue 4, 2012, Pages 16~23
DOI : 10.6112/kscfe.2012.17.4.016
Current display manufacturing processes apply thermal treatment of glass backplanes widely for hydrogen degassing, crystallization of thin-films, tempering, forming, and precompaction. Estimation of the characteristics of transient heating stages and thermal non-uniformities on a single glass substrate or in a stack of glasses are extremely helpful to understand non-homogeneity of mechanical and electronic features of nano/micro structures of end products. Based on simple heat transfer models and using an electric muffle furnace, temperature variations in a glass stack were predicted and measured for glass backplanes of
in size and 0.7 mm in thickness. Except for the period of putting glass backplanes into the furnace, thermal radiation was the major heating mechanism for the treatment and theoretical predictions agreed well to the experimental temperatures on the backplanes. Using the theoretical model, thermal fields for a glass stack of glass-size,
, and of the number of sheets, 1 to 12, were calculated for practical design and manufacturing of the muffle furnace for large-scale displays, e.g. up to
EFFECT OF LENGTH-SCALE IN DDES FOR BACKWARD-FACING STEP FLOW
Lee, C.Y. ; Sa, J.H. ; Park, S.H. ; Lee, E.S. ; Lee, J.I. ; Lee, K.S. ;
Journal of computational fluids engineering, volume 17, issue 4, 2012, Pages 24~31
DOI : 10.6112/kscfe.2012.17.4.024
Effects of the subgrid length-scale in the Delayed-Detached Eddy Simulation(DDES) are investigated based on the Spalart-Allmaras(S-A) and the k-
Shear Stress Transport(SST) turbulence models. Driver & Seegmiller's experimental results are used to validate numerical results. Grid convergence with grid resolution and subgrid length-scale is investigated. The simulation results show that the volume method for the subgrid length-scale is more resistant to unfavorable effects of the grid size in the periodic direction than the maximum method. Using a sufficient grid resolution and an appropriate subgrid length-scale, both S-A based DDES and SST based DDES methods can provide a good correlation with the experimental data.
A STUDY ON CONSTRAINED EGO METHOD FOR NOISY CFD DATA
Bae, H.G. ; Kwon, J.H. ;
Journal of computational fluids engineering, volume 17, issue 4, 2012, Pages 32~40
DOI : 10.6112/kscfe.2012.17.4.032
Efficient Global Optimization (EGO) method is a global optimization technique which can select the next sample point automatically by infill sampling criteria (ISC) and search for the global minimum with less samples than what the conventional global optimization method needs. ISC function consists of the predictor and mean square error (MSE) provided from the kriging model which is a stochastic metamodel. Also the constrained EGO method can minimize the objective function dealing with the constraints under EGO concept. In this study the constrained EGO method applied to the RAE2822 airfoil shape design formulated with the constraint. But the noisy CFD data caused the kriging model to fail to depict the true function. The distorted kriging model would make the EGO deviate from the correct search. This distortion of kriging model can be handled with the interpolation(p=free) kriging model. With the interpolation(p=free) kriging model, however, the search of EGO solution was stalled in the narrow feasible region without the chance to update the objective and constraint functions. Then the accuracy of EGO solution was not good enough. So the three-step search method was proposed to obtain the accurate global minimum as well as prevent from the distortion of kriging model for the noisy constrained CFD problem.
COMPUTATIONAL FLUID DYNAMICS ANALYSIS OF THERMAL STRATIFICATION IN THE UPPER PLENUM OF THE MONJU FAST BREEDER REACTOR
Choi, S.K. ; Lee, T.H. ;
Journal of computational fluids engineering, volume 17, issue 4, 2012, Pages 41~48
DOI : 10.6112/kscfe.2012.17.4.041
A numerical analysis of thermal stratification in the upper plenum of the MONJU fast breeder reactor was performed. Calculations were performed for a 1/6 simplified model of the MONJU reactor using the commercial code, CFX-13. To better resolve the geometrically complex upper core structure of the MONJU reactor, the porous media approach was adopted for the simulation. First, a steady state solution was obtained and the transient solutions were then obtained for the turbine trip test conducted in December 1995. The time dependent inlet conditions for the mass flow rate and temperature were provided by JAEA. Good agreement with the experimental data was observed for steady state solution. The numerical solution of the transient analysis shows the formation of thermal stratification within the upper plenum of the reactor vessel during the turbine trip test. The temporal variations of temperature were predicted accurately by the present method in the initial rapid coastdown period (~300 seconds). However, transient numerical solutions show a faster thermal mixing than that observed in the experiment after the initial coastdown period. A nearly homogenization of the temperature field in the upper plenum is predicted after about 900 seconds, which is a much shorter-term thermal stratification than the experimental data indicates. This discrepancy is due to the shortcoming of the turbulence models available in the CFX-13 code for a natural convection flow with thermal stratification.
3D GEOMETRY EFFECTS ANALYSIS ON PROPAGATION OF PRESSURE WAVE GENERATED BY HIGH-SPEED TRAIN TRAVELING IN A TUNNEL USING CFD
Shin, D.Y. ; Lee, S.G. ; Oh, H.J. ; Kim, H.G. ; Yoon, S.H. ; Kim, C.J. ;
Journal of computational fluids engineering, volume 17, issue 4, 2012, Pages 49~55
DOI : 10.6112/kscfe.2012.17.4.049
Research has importance in proposing the design of a tunnel with a vertical vent to secure passengers in a comfortable environment and safe against pressure. Using several analysis methods, the magnitude of the pressure induced by the vertical vent in the tunnel can be analyzed. In addition to the 3-dimensional method, the 2-dimensional method and the 2-dimensional axis-symmetric method are also used to analyze the strong and weak points of each so that the optimum analysis method can be obtained. As a result, it appears that the 2-dimensional axis-symmetric method is the most suitable in analyzing tunnel pressure consider to accuracy and time effective aspect. Also, the 3-dimensional method is disadvantageous in that it takes longer in calculating results, but is more effective in predicting phenomena around the vertical vent in the tunnel.
SHAPE OPTIMIZATION OF UCAV FOR AERODYNAMIC PERFORMANCE IMPROVEMENT AND RADAR CROSS SECTION REDUCTION
Jo, Y.M. ; Choi, S.I. ;
Journal of computational fluids engineering, volume 17, issue 4, 2012, Pages 56~68
DOI : 10.6112/kscfe.2012.17.4.056
Nowadays, Unmanned Combat Air Vehicle(UCAV) has become an important aircraft system for the national defense. For its efficiency and survivability, shape optimization of UCAV is an essential part of its design process. In this paper, shape optimization of UCAV was processed for aerodynamic performance improvement and Radar Cross Section(RCS) reduction using Multi Objective Genetic Algorithm(MOGA). Lift and induced drag, friction drag, RCS were calculated using panel method, boundary layer theory, Physical Optics(PO) approximation respectively. In particular, calculation applied Radar Absorbing Material(RAM) was performed for the additional RCS reduction. Results are indicated that shape optimization is performed well for improving aerodynamic performance, reducing RCS. Further study will be performed with higher fidelity tools and consider other design segments including structure.
CALCULATION OF SHOCK STAND-OFF DISTANCE FOR A SPHERE IN NONEQUILIBRIUM HYPERSONIC FLOW
Furudate, M. Ahn ;
Journal of computational fluids engineering, volume 17, issue 4, 2012, Pages 69~74
DOI : 10.6112/kscfe.2012.17.4.069
Hypersonic flowfields over a sphere is calculated by using a nonequilibrium flow solver. The flow solver features a two-temperature model and finite rate chemical reaction models to describe nonequilibrium thermochemical processes. For the purpose of validation, the calculated shock stand-off distance is compared with the experimental data which is measured in a ballistic range facility. The present nonequilibrium calculation well reproduced the experimental shock stand-off distance in the cases where the experimental flowfields are expected to be nearly equilibrium, as well as in the cases to be nonequilibrium flowfields in the velocity range 4000 to 5500 m/s.
A NUMERICAL ANALYSIS ON THE BEHAVIOR OF LIQUID FILM AROUND A CURVED EDGE
Lee, Geonkang ; Hur, Nahmkeon ; Son, Gihun ;
Journal of computational fluids engineering, volume 17, issue 4, 2012, Pages 75~80
DOI : 10.6112/kscfe.2012.17.4.075
Due to the effect of surface tension, liquid film around a curved edge of solid surface moves from the corner to the flat surface. During this behavior of liquid film, film sagging phenomenon is easily occurred at the solid surface. Behavior of liquid film is determined with the effects of the properties of liquid film and the geometric factors of solid surface. In the present study, 2-D transient CFD simulations were conducted on the behavior of liquid film around a curved edge. The two-phase interfacial flow of liquid film was numerically investigated by using a VOF method in order to predict the film sagging around a curved edge. In the steady state of behavior of liquid film, the liquid film thickness of numerical result showed a good agreement with experimental data. After verifying the numerical results, the characteristics of behavior of liquid film were numerically analyzed with various properties of liquid film such as surface tension coefficient and viscosity. The effects of geometric factors on film sagging were also investigated to reduce the film sagging around a curved edge.
PERFORMANCE ASSESSMENT OF THE RANS TURBULENCE MODELS IN PREDICTION OF AERODYNAMIC NOISE FOR AIR-CONDITIONER INDOOR UNIT
Min, Y.H. ; Kang, S. ; Hur, N. ; Lee, C. ; Park, J. ;
Journal of computational fluids engineering, volume 17, issue 4, 2012, Pages 81~86
DOI : 10.6112/kscfe.2012.17.4.081
The objective of the present study is to investigate the effects of various turbulence models on the aerodynamic noise of an air-conditioner (AC) indoor unit. The results from URANS (unsteady Reynolds-averaged Navier-Stokes) simulations with the standard k-
shear stress transport (SST) and Spalart-Allmaras (S-A) turbulence models were analyzed and compared with the noise data from the experiments. The frequency spectra of the far-field acoustic pressure were computed using the Farrasat equation derived from the Ffowcs Williams-Hawkings (FW-H) equation based on the acoustic analogy model. Two fixed fan casings and the rotating cross-flow fan were used as the source surfaces of the dipole noise in the Farrasat equation. The result with the standard k-
model showed a much better agreement with the experimental data compared to the k-w SST and S-A models. The differences in the pressure spectra from the different turbulence models were discussed based on the instantaneous vorticity fields. It was found that the over-estimated power spectra with the k-w SST and S-A models are related to the emphasized small-scale vortices produced with these models.
NUMERICAL STUDY OF TRANSIENT CONJUGATE HEAT TRANSFER IN A MICRO-CHANNEL SUBSTRATE
Lee, H.J. ;
Journal of computational fluids engineering, volume 17, issue 4, 2012, Pages 87~92
DOI : 10.6112/kscfe.2012.17.4.087
A numerical study of transient conjugate heat transfer on micro heater in a micro-channel substrate under pulsed heating was conducted. It was found that the time constant is not affected by the pulse heating magnitude at same operating condition. Furthermore, the time constant increases with low substrate thermal diffusivity, low Reynolds number, and large channel diameter. Since the time constant is a dominant parameter to characterize transient heat transfer, it should be considered for transient convective heat transfer coefficient.
THE EFFECTS OF MACH NUMBER AND THICKNESS RATIO OF AIRFOIL ON TRANSONIC FLOW OF MOIST AIR AROUND A THIN AIRFOIL WITH LATENT HEAT TRANSFER
Lee, J.C. ;
Journal of computational fluids engineering, volume 17, issue 4, 2012, Pages 93~102
DOI : 10.6112/kscfe.2012.17.4.093
Once the condensation of water vapor in moist air around a thin airfoil occurs, liquid droplets nucleate. The condensation process releases heat to the surrounding gaseous components of moist air and significantly affects their thermodynamic and flow properties. As a results, variations in the aerodynamic performance of airfoils can be found. In the present work, the effects of upstream Mach number and thickness ratio of airfoil on the transonic flow of moist air around a thin airfoil are investigated by numerical analysis. The results shows that a significant condensation occurs as the upstream Mach number is increased at the fixed thickness ratio of airfoil(
=0.12) and as the thickness ratio of airfoil is increased at the fixed upstream Mach number(
=0.80). The condensate mass fraction is also increased and dispersed widely around an airfoil as the upstream Mach number and thickness ratio of airfoil are increased. The position of shock wave for moist air flow move toward the leading edge of airfoil when it is compared with the position of shock wave for dry air.
COMPUTATION OF SOUND SCATTERING IN 3D COMPLEX GEOMETRY BY BRINKMAN PENALIZATION METHOD
Lee, S.H. ; Lee, J.B. ; Kim, J.U. ; Moon, Y.J. ;
Journal of computational fluids engineering, volume 17, issue 4, 2012, Pages 103~109
DOI : 10.6112/kscfe.2012.17.4.103
Sound scattering in 3D complex geometry is difficult to model with body-fitted grid. Thus Brinkman Penalization method is used to compute sound scattering in 3D complex geometry. Sound propagation of monitor/TV is studied. The sound field for monitor/TV is simulated by applying Brinkman Penalization method to Linearized Euler Equation. Solid Structure and ambient air are represented as penalty terms in Linearized Euler Equation.