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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 15, Issue 4 - Dec 2010
Volume 15, Issue 3 - Sep 2010
Volume 15, Issue 2 - Jun 2010
Volume 15, Issue 1 - Mar 2010
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DEVELOPMENT OF A MODIFIED
TURBULENCE MODEL FOR VISCO-ELASTIC FLUID AND ITS APPLICATION TO HEMODYNAMICS
Ro, K.C. ; Ryou, H.S. ;
Journal of computational fluids engineering, volume 15, issue 4, 2010, Pages 1~8
This article describes the numerical investigation of turbulent blood flow in the stenosed artery bifurcation under periodic acceleration of the human body. Numerical analyses for turbulent blood flow were performed with different magnitude of periodic accelerations using a modified turbulence model which was considering drag reduction of non-Newtonian fluid. The blood was considered to be a non-Newtonian fluid which was based on the power-law viscosity. In order to validate the modified
model, numerical simulations were compared with the standard
model and the Malin's low Reynolds number turbulence model for power-law fluid. As results, the modified
model represents intermediate characteristics between laminar and standard
model, and the modified
model showed good agreements with Malin's verified power law model. Moreover, the computing time and computer resource of the modified
model were reduced about one third than low Reynolds number model including Malin's model.
NUMERICAL STUDY ON THE MIXER TYPES OF UREA-SCR SYSTEM FOR FLOW MIXING IMPROVEMENT
Lee, J.W. ; Choi, H.K. ; Yoo, G.J. ;
Journal of computational fluids engineering, volume 15, issue 4, 2010, Pages 9~16
To alleviate NOx emission, a variety of approaches has been applied. In marine diesels, the application of SCR systems has been considered an effective exhaust aftertreatment method for NOx emission control. Most current SCR systems use a various catalyst for the reaction of ammonia with NOx to form nitrogen and water. In theory, it is possible to achieve 100% NOx if the
-to-NOx ratio is 1:1. However, the reaction has a limited non-uniformity of the exhaust gas flow and ammonia concentration distribution. Therefore, it is necessary to investigate the optimum flow conditions. In order to achieve uniform flow at monolith front face, we are equipped with a various mixed devices. In this paper, it is presented that the mixed devices play an important role improvement of flow patterns and particle distributions of
by numerical simulation.
STUDY ON PROPERTIES OF INTERIOR BALLISTICS ACCORDING TO SOLID PROPELLANT POSITION IN CHAMBER
Jang, J.S. ; Sung, H.G. ; Lee, S.B. ; Roh, T.S. ;
Journal of computational fluids engineering, volume 15, issue 4, 2010, Pages 17~24
Using the numerical code for the interior ballistics, the performance of the interior ballistics with the characteristics according to the position of the solid propellant in chamber has been investigated. In existing research, propellants have been evenly distributed in the chamber. In this study, however, several cases of the existence of empty space in the chamber at which the propellants are not evenly distributed are considered. The 7-perforated propellant configuration has been used in this research. The results have shown the change of performance of the interior ballistics according to solid propellant positions in the chamber.
NUMERICAL STUDY ON DROPLET SPREAD MOTION AFTER IMPINGEMENT ON THE WALL USING IMPROVED CIP METHOD
Son, S.Y. ; Ko, G.H. ; Lee, S.H. ; Ryou, H.S. ;
Journal of computational fluids engineering, volume 15, issue 4, 2010, Pages 25~31
Interface tracking of two phase is significant to analyze multi-phase phenomena. The VOF(Volume of Fluid) and level set are well known interface tracking method. However, they have limitations to solve compressible flow and incompressible flow at the same time. CIP(Cubic Interpolate Propagation) method is appropriate for considering compressible and incompressible flow at once by solving the governing equation which is divided up into advection and non-advection term. In this article, we analyze the droplet impingement according to various We number using improved CIP method which treats nonlinear term once more comparison with original CIP method. Furthermore, we compare spread radius after droplet impingement on the wall with the experimental data and original CIP method. The result using improved CIP method shows the better result of the experiments, comparison with result of original CIP method, and it reduces the mass conservation error which is generated in the numerical analysis comparison with original CIP method.
NUMERICAL STUDY OF MODULATED TAYLOR-COUETTE FLOW
Kang, Chang-Woo ; Yang, Kyung-Soo ; Mutabazi, Innocent ;
Journal of computational fluids engineering, volume 15, issue 4, 2010, Pages 32~39
In this study, we consider Taylor-Couette flow with the outer cylinder at rest and the inner one oscillating with a mean angular velocity. Varying the mean angular velocity, amplitude and frequency of the oscillation, we investigate the characteristics of modulated Taylor vortices. At a constant mean angular velocity, Taylor vortices intensify as the amplitude increases and frequency decreases. The axial wavenumber is calculated by spectral analysis. When the frequency varies, the axial wavenumber does not change at a constant mean angular velocity and amplitude. But, the axial wavenumber increases, as the mean angular velocity increases.
SIMULATION OF A MICROPUMP WITH STEP ELECTRODES
Kim, Byoung-Jae ; Lee, Seung-Hyun ; Sung, Hyung-Jin ;
Journal of computational fluids engineering, volume 15, issue 4, 2010, Pages 40~45
The flow rate is higher in ACEO micro-pumps with step electrodes than in micro-pumps with planar asymmetric electrodes. In the present study, numerical simulations were made of a ACEO micro-pump with step electrodes to investigate the effects of electrode design parameters on the pumping flow rate. The electrical charge at the electrodes, the fluid flow, and potential were solved, taking into account the finite size of ions, that is, the steric effect. This effect is recognized to be capable of quantifying the electrical charge more accurately in the electrical double layer subject to high voltages. Geometrical parameters such as heights, widths, and gaps of three-dimensional electrodes were optimized to enhance the pumping flow rate. Moreover, the effect of amplitude and frequency of AC was studied.
FLOW CONTROL ON ELLIPTIC AIRFOILS USING SYNTHETIC JET
Kim, S.H. ; Kim, C.W. ;
Journal of computational fluids engineering, volume 15, issue 4, 2010, Pages 46~52
In the present work, the aerodynamic characteristics of elliptic airfoils which have a 12% thickness ratio are numerically investigated based on Reynolds-averaged Navier-Stokes equations and a transition SST model at a Reynolds number 8.0
105. The numerical simulation of a synthetic jet actuator which is a well-known zero-net-mass active flow control actuator located at x/c = 0.00025, was performed to control massive flow separation around the leading edge of the elliptic airfoils. Four cases of non-dimensional frequencies were simulated at an angle of attack of 12 degree. It is found that the size of the vortex induced by synthetic jets was getting smaller as the jet frequency becomes higher. Comparison of the location of synthetic jets between x/c = 0.00025 (around the leading edge) and x/c = 0.9 (near the separation) shows that the control near the leading edge induces closed recirculation flow regions caused by the interaction of the synthetic jet with the external flow, but the control applied at 0.9c (near the trailing edge) induces a very small and weak vortex which quickly decays due to weak intensity.
NUMERICAL STUDY ON WIND TUNNEL GROUND PLATE WITH A PRESSURE CONTROL DEVICE
Lee, M.J. ; Kim, C.W. ;
Journal of computational fluids engineering, volume 15, issue 4, 2010, Pages 53~59
Preliminary design of a ground plate, a device installed close to the aircraft model for wind tunnel test to simulate the ground effect, was performed by a numerical simulation. A two-dimensional numerical study was performed initially to decide the optimal leading edge and flap configurations. Then, three-dimensional studies were conducted to decide the optimal flap deflection angle for pressure distribution reduction since the plate and the plate supporting system generate static pressure difference between the upper and lower flow regions. Three-dimensional simulation additionally studied the effect of the clearance between the plate and the wind tunnel side wall. For the efficiency of computation, half model was simulated and a symmetric boundary condition was applied on the center plane. Based on the preliminary design, a ground plate was designed, manufactured and tested at the Korea Aerospace Research Institute(KARI) wind tunnel. The measured pressure differences versus flap deflection angle agreed well with the predicted results.
NUMERICAL ANALYSIS OF UNSTEADY FLOW FIELD AND AEROACOUSTIC NOISE OF AN AXIAL FLOW FAN
Kim, Wook ; Hur, Nahm-Keon ; Jeon, Wan-Ho ;
Journal of computational fluids engineering, volume 15, issue 4, 2010, Pages 60~66
Unsteady Reynolds Averaged Navier-Stokes(URANS) and Large Eddy Simulation(LES) simulation of an axial flow fan are calculated upon same conditions and computational grids in order to study aeroacoustic noise of an axial flow fan numerically. Results of computed performance and predicted noise are compared with those of measurement. Both performances show accurate results with a significant difference of less than 5%. However, noise of LES result is more close to measured noise qualitatively than URANS. Levels of tonal noises of both LES and URANS are quite similar with those of measured at BPF(Blade Passing Frequency) in sound spectrum. However, as leading edge separation and tip vortex shedding phenomena of LES are showed more clearly than those of URANS, sound level of broadband noise of LES corresponds better than that of URANS, especially.
NUMERICAL METHOD FOR EVALUATION OF HYDROGEN FLAME ACCELERATION IN A COMPARTMENT OF A NUCLEAR POWER PLANT
Kim, Jong-Tae ; Kim, Sang-Baik ; Kim, Hoo-Joong ;
Journal of computational fluids engineering, volume 15, issue 4, 2010, Pages 67~75
Hydrogen safety is one of important issues for future public usage of hydrogen. When hydrogen is released in a compartment, the occurrence of detonation must be prohibited. In order to evaluate the possibility of DDT (Deflagration to Detonation Transition) in the compartment with the hydrogen release, sigma-lambda criteria which were developed from experimental data are commonly used. But they give a little conservative results because they do not consider the detailed geometrical effect of the compartment. This is the main reason of the need to mechanistic combustion model for evaluation of hydrogen flame propagation and acceleration. In this study, sigma-lambda criteria and combustion model were systematically applied to evaluate a possibility of DDT in a IRWST compartment of APR1400 nuclear power plant during a hypothetical accident. A combustion model in an open source CFD code OpenFOAM has been applied for analyses of hydrogen flame propagation. The model was validated by evaluating the flame acceleration tests conducted in FLAME facility. And it was applied to evaluate the characteristics of a hydrogen flame propagation in the IRWST compartment of APR1400.
DEVELOPMENT OF EFFICIENT HARMONIC BALANCE METHOD WITH THE MULTIGRID METHOD
Im, D.K. ; Park, S.H. ; Kwon, J.H. ;
Journal of computational fluids engineering, volume 15, issue 4, 2010, Pages 76~84
In order to analyze the periodic unsteady flow problem efficiently the partially implicit harmonic balance (PIHB) method was developed. Contrary to the existing harmonic balance method, this method handles the harmonic source term explicitly and deals with flux terms implicitly. This method has a good convergence in comparison with the full explicit harmonic method and it is easy to apply this method because there is no need to calculate the complicated flux Jacobian term by comparing with the full implicit harmonic method. With the multigrid method about the each harmonic it turns out that this method has a good convergence regardless of the number of harmonics. The oscillating flows over NACA0012 airfoil is considered to verify this method then the result correponsed to both the result of dual time stepping and explicit Runge-Kutta method.
AERODYNAMIC ANALYSIS AND COMPARISON OF EXPERIMENTAL DATA FOR 2-BLADED VERTICAL AXIS WIND TURBINE
Hwang, M.H. ; Kim, D.H. ; Lee, J.W. ; Oh, M.W. ; Kim, M.H. ; Ryu, G.J. ;
Journal of computational fluids engineering, volume 15, issue 4, 2010, Pages 85~91
In this study, aerodynamic analyses based on unsteady computational fluid dynamics (CFD) have been conducted for a 2-bladed vertical-axis wind turbine (VAWT) configuration. Reynolds-averaged Navier-Stokes equations with standard
turbulence models are solved for unsteady flow problems. The experiment model of 2-bladed VAWT has been designed and tested in this study. Aerodynamic experiment of the present VAWT model are effectively conducted using the vehicle mounted testing system. The comparison result between the experiment and the computational fluid dynamics (CFD) analysis are presented in order to verify the accuracy of CFD modeling with different turbulent models.
HELIUM CONCENTRATION DECREASE DUE TO AIR ENTRAINMENT INTO GLASS FIBER COOLING UNIT IN A HIGH SPEED OPTICAL FIBER DRAWING PROCESS
Kim, K. ; Kim, D. ; Kwak, H.S. ; Park, S.H. ; Song, S.H. ;
Journal of computational fluids engineering, volume 15, issue 4, 2010, Pages 92~98
In a modern high speed drawing process of optical fibers, it is necessary to use helium as a cooling gas in a glass fiber cooling unit in order to sufficiently cool down the fast moving glass fiber freshly drawn from the heated silica preform in the furnace. Since the air is entrained unavoidably when the glass fiber passes through the cooling unit, the helium is needed to be injected constantly into the cooling unit. The present numerical study investigates and analyzes the air entrainment using an axisymmetric geometry of glass fiber cooling unit. The effects of helium injection rate and direction on the air entrainment rate are discussed in terms of helium purity of cooling gas inside the cooling unit. For a given rate of helium injection, it is found that there exists a certain drawing speed that results in sudden increase in the air entrainment rate, which leads to the decreasing helium purity and therefore the cooling performance of the glass fiber cooling unit. Also, the helium injection in aiding direction is found to be more advantageous than the injection in opposing direction.
FRACTIONAL STEP METHOD COMBINED WITH VOLUME-OF-FLUID METHOD FOR EFFICIENT SIMULATION OF UNSTEADY MULTIPHASE FLOW
Lee, Kyong-Jun ; Yang, Kyung-Soo ; Kang, Chang-Woo ;
Journal of computational fluids engineering, volume 15, issue 4, 2010, Pages 99~108
Fractional Step Methods(FSM) are popular in simulation of unsteady incompressible flow. In this study, we demonstrate that FSM, combined with a Volume-Of-Fluid method, can be further applied to simulation of multiphase flow. The interface between the fluids is constructed by the effective least squares volume-of-fluid interface reconstruction algorithm and advected by the velocity using the operator split advection algorithm. To verify our numerical methodology, our results are compared with other authors' numerical and experimental results for the benchmark problems, revealing excellent agreement. The present FSM sheds light on accurate simulation of turbulent multiphase flow which is found in many engineering applications.
ANALYSIS ON CHARACTERISTICS OF AN AXIAL FLOW FAN THROUGH CFD ANALYSIS INCORPORATED WITH MOTOR CHARACTERISTICS
Kim, J.H. ; Hur, N. ; Kim, W. ;
Journal of computational fluids engineering, volume 15, issue 4, 2010, Pages 109~114
In a fan design, CFD analysis, which is very useful for mechanical design relating to the heat and fluid dynamics, is one of the most popular tools. However, since the CFD analysis is conventionally carried out with the constant fan speed condition, the speed change, induced by the air flow rate and motor characteristics, is hardly modeled. And, consequently, the remarkable difference exist between analysis and experimental results. In this paper, we has proposed a method of setting the varying fan speed as a boundary condition considering air flow rate and motor torque-speed characteristics. The effectiveness of the proposed method is verified by comparison with experimental results.