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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 2 - Jun 2016
Volume 21, Issue 1 - Mar 2016
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COMPUTATIONAL ANALYSIS OF AN ELECTRO-THERMAL ICE PROTECTION SYSTEM IN ATMOSPHERIC ICING CONDITIONS
Raj, L.P. ; Myong, R.S. ;
Journal of computational fluids engineering, volume 21, issue 1, 2016, Pages 1~9
DOI : 10.6112/kscfe.2016.21.1.001
Atmospheric icing may have significant effects not only on safety of aircraft in air, but also on performance of wind turbine and power networks on ground. Thus, ice protection measure should be developed to protect these systems from icing hazards. A very efficient method is the electro-thermal de-icing based on a process by which ice accretion is melted and blown away through aerodynamic forces. In this computational study, a state-of-the-art icing code, FENSAP-ICE, was used for the analysis of electro thermal de-icing system. Computational results including detailed conjugate heat transfer analysis were then validated with experimental data. Further, the computational model was applied to the DU21 airfoil section of NREL 5MW wind turbine with calculated heater parameters.
AN UNSTRUCTURED STEADY COMPRESSIBLE NAVIER-STOKES SOLVER WITH IMPLICIT BOUNDARY CONDITION METHOD
Baek, C. ; Kim, M. ; Choi, S. ; Lee, S. ; Kim, C.W. ;
Journal of computational fluids engineering, volume 21, issue 1, 2016, Pages 10~18
DOI : 10.6112/kscfe.2016.21.1.010
Numerical boundary conditions are as important as the governing equations when analyzing the fluid flows numerically. An explicit boundary condition method updates the solutions at the boundaries with extrapolation from the interior of the computational domain, while the implicit boundary condition method in conjunction with an implicit time integration method solves the solutions of the entire computational domain including the boundaries simultaneously. The implicit boundary condition method, therefore, is more robust than the explicit boundary condition method. In this paper, steady compressible 2-Dimensional Navier-Stokes solver is developed. We present the implicit boundary condition method coupled with LU-SGS(Lower Upper Symmetric Gauss Seidel) method. Also, the explicit boundary condition method is implemented for comparison. The preconditioning Navier-Stokes equations are solved on unstructured meshes. The numerical computations for a number of flows show that the implicit boundary condition method can give accurate solutions.
VALIDATION OF A DESIGN CODE FOR SODIUM-TO-SODIUM HEAT EXCHANGERS BY UTILIZING COMPUTATIONAL FLUID DYNAMICS
Kim, D. ; Eoh, J.H. ; Lee, T.H. ;
Journal of computational fluids engineering, volume 21, issue 1, 2016, Pages 19~29
DOI : 10.6112/kscfe.2016.21.1.019
A Prototype Gen-IV Sodium-cooled Fast Reactor which is one of the
generation nuclear reactors is in development by Korea Atomic Energy Research Institute. The reactor is composed of four main fluid systems which are categorized by its functions, i.e., Primary Heat Transport System, Intermediate Heat Transport System, Decay Heat Removal System and Sodium-Water Reaction Pressure Relief System. The coolant of the reactor is liquid sodium and sodium-to-sodium heat exchangers are installed at the interfaces between two fluid systems, Intermediate Heat Exchangers between the Primary Heat Transport System and the Intermediate Heat Transport System and Decay Heat Exchangers between the Primary Heat Transport System and the Decay Heat Removal System. For the design and performance analysis of the Intermediate Heat Exchanger and the Decay Heat Exchanger, a computer code was written during previous step of research. In this work, the computer code named "SHXSA" has been validated preliminarily by computational fluid dynamics simulations.
COARSE GRID LARGE-EDDY SIMULATION OF FLOW OVER A HEAVY VEHICLE
Lee, S. ; Kim, M. ; You, D. ; Kim, J.J. ; Lee, S.J. ;
Journal of computational fluids engineering, volume 21, issue 1, 2016, Pages 30~35
DOI : 10.6112/kscfe.2016.21.1.030
In order to investigate effects of grid resolution on large-eddy simulation of flow over a heavy vehicle, large-eddy simulations over the vehicle with coarse grid and fine grid are conducted. In addition, comparison of drag coefficients with the experimental data obtained by a wind tunnel experiment is conducted. Both of the drag coefficients of coarse grid and fine grid large-eddy simulation show good agreement with the experimental data. Flow fields obtained by the coarse and the fine grid large-eddy simulation are compared in the vehicle frontal-face region, the vehicle rear wheel region, and the vehicle base region. Coarse grid large-eddy simulation shows good agreement with the fine grid large-eddy simulation in the vehicle front face region and the vehicle rear wheel region, since the flow over the present vehicle is dominated by flow separation which is geometrically pre-determined, not by the skin friction which is known to be sensitive to grid resolution.
A STUDY ON THE GRID GENERATION FOR TWO-DIMENSIONAL FLOW USING A POTENTIAL SOLVER
Lee, J. ; Jung, K. ;
Journal of computational fluids engineering, volume 21, issue 1, 2016, Pages 36~42
DOI : 10.6112/kscfe.2016.21.1.036
One of the obstacles on the grid generation for complex geometries with multi-block structured grids is the domain decomposition. In this paper, the domain decomposition for two-dimensional flow is studied using the flow characteristics. The potential flow equation with the source distribution on the panel surface is solved to extract the information of the flow. The current approach is applied to a two-dimensional cylinder and Bi-NACA0012 problems. The generated grids are applied to generic flow solvers and reasonable results are obtained. It can be concluded that the current methods is useful in the domain decomposition for the multi-block structured grid.
THE CHARACTERISTICS OF HEAT TRANSFER AND CHEMICAL REACTION FOR THERMAL CRACKING OF ETHANE IN TUBULAR REACTOR
Shin, C.Y. ; Ahn, J. ;
Journal of computational fluids engineering, volume 21, issue 1, 2016, Pages 43~49
DOI : 10.6112/kscfe.2016.21.1.043
Thermal cracking is commonly modeled as plug flow reaction, neglecting the lateral gradients present. In this paper, 2-dimensional computational fluid dynamics including turbulence model and molecular reaction scheme are carried out. This simulation is solved by means of coupled implicit scheme for stable convergence of solution. The reactor is modeled as an isothermal tube, whose length is 1.2 m and radius is 0.01 m, respectively. At first, The radial profile of velocity and temperature at each point are predicted in its condition. Then the bulk temperature and conversion curve along the axial direction are compared with other published data to identify the reason why discussed variations of properties are important to product yield. Finally, defining a new non-dimensional number, Effect of interaction with turbulence, heat transfer and chemical reaction are discussed for design of thermal cracking furnace.
NUMERICAL STUDY ON THE FLOW CHARACTERISTICS OF A HYDRAULIC PISTON PUMP BASED ON THE ANGLE OF THE SWASH-PLATE AND THE DISCHARGE PRESSURE
Yoon, J.H. ; Lee, K. ; Kang, M.C. ;
Journal of computational fluids engineering, volume 21, issue 1, 2016, Pages 50~57
DOI : 10.6112/kscfe.2016.21.1.050
In various industries related with construction and military machinery, a large amount of power is normally required because such machinery operations, such as digging or breaking, take place under difficult working conditions in a rough environment. Thus, a hydraulic system needs to be applied as the major power transfer system. To produce and supply hydraulic power depending on the various load conditions, a hydraulic piston pump is utilized as a typical power source for a hydraulic system. In the present study, numerical simulations were conducted using the commercial program, Ansys CFX 14.5. To lubricate the moving parts as the pump starts to operate, a small amount of oil leaks out through the clearance between the orifice in the piston-shoe and the recess at the swash-plate. Taking this into consideration, a cylindrically shaped computational domain was modeled to maintain the same equivalent leakage area. To validate the numerical method applied herein, the numerical results of the flow rate at the discharge port were compared with the experimental data, and a good agreement between them was shown. Using the verified method, the effects of the discharge pressure and the angle of the swash-plate were also evaluated under several load conditions. The results of the present study can be useful information for a hydraulic piston pump used in many different manufacturing industries.
FLOW ANALYSIS OF THE IMPELLER WITH DIFFERENT INLET ANGLES IN THE CENTRIFUGAL PUMP
Lee, S.H. ; Lee, D.R. ;
Journal of computational fluids engineering, volume 21, issue 1, 2016, Pages 58~63
DOI : 10.6112/kscfe.2016.21.1.058
This research is to investigate the performance analysis for efficient design with four different inlet angles of the centrifugal pump impeller. Assuming that the rotation speed and exit angle are fixed, Four cases of the centrifugal pumps were numerically analyzed using ANSYS FLUENT. According to the numerical results, head and pump efficiency at inlet angle of 20 degrees was highest. There is no big difference of efficiency at inlet angle of 20 degrees compared to the inlet angle 30 degrees. About 15% of efficiency at inlet angle of 20 degrees is higher than inlet angle of 40 degrees and 31% higher than inlet angle oof 50 degrees. Because there is liner functional relationship between speed and flow rate, suction flow rate at inlet angle of 20 degrees is superior to the inlet angle of 30 degrees as much as 0.89%, inlet angle of 40 degrees as 13%, inlet angle of 50 as 28.4%. Head at inlet angle of 20 degrees is superior to the inlet angle of 30 degrees as much as 0.4%, inlet angle of 40 degrees as 2.7%, inlet angle of 50 degrees as 3.2%. There should exist highest efficiency and also optimal design shape at inlet angle of 20 degrees.
STUDY ON COOLING PERFORMANCE BY CONVECTIVE HEAT TRANSFER WITH DIFFERENT DISK BRAKE SHAPES
Park, C.W. ; Lee, D.R. ;
Journal of computational fluids engineering, volume 21, issue 1, 2016, Pages 64~71
DOI : 10.6112/kscfe.2016.21.1.064
This research is to numerically investigate the convective cooling performance in the Disk brake. Research concentrates on the heat transfer coefficient and cooling performance which are selected with cooling local locations. Cooling performance of the Hole disk has been compared by Ventilated Disk. According to the results of heat transfer on the disk brake, activated velocity distributions more appear in the Hole disk. This is due to the fact that a number of hole units have exactly 120 on the surface of the hole disk. Therefore, velocity distributions of hole disk brake is better activated than Ventilated disk. According to the calculations of Nusselt number between surface and atmosphere in the interested cooling area, average value of cooling effect has been increased 13.5% by the hole disk at driving of speed 65 km/h situation and grown 18% by the hole disk at driving speed of 100 km/h. Due to the flow of air through the hole route, cooling performance of the hole disk was very excellent. In addition, cooling effect on edge of the bottom is better than the vicinity of center.
NUMERICAL STUDY ON DPS THRUSTER-HULL INTERACTION WITH DIFFERENT AXIS TILTING ANGLE
Jin, D.-H. ; Lee, S.-W. ;
Journal of computational fluids engineering, volume 21, issue 1, 2016, Pages 72~77
DOI : 10.6112/kscfe.2016.21.1.072
In this study, effects of thurster axis tilting angle on the thruster-hull interaction and propulsion performance in a dynamic positioning system of offshore plant are numerically investigated. Straight and 7-degree tilted downward thruster models as a form of ducted propeller are considered. For numerical simulations, Reynolds averaged Navier-Stokes equations with SST turbulence model are solved by using STAR-CCM+. Results show that thruster-hull interaction is reduced in 7-degree tilted thruster model with lower vortex strength between thruster and hull bottom, although the propulsion performance does not have noticeable difference in a bollard condition.
MOTION DESIGN OPTIMIZATION OF AUV DOUBLE HYDROFOIL FOR IMPROVEMENT OF THRUST AND EFFICIENCY
So, H.K. ; Jo, T.H. ; Lee, Y.H. ; Kim, J.S. ; Han, J.H. ; Koo, B.C. ; Lee, D.H. ;
Journal of computational fluids engineering, volume 21, issue 1, 2016, Pages 78~85
DOI : 10.6112/kscfe.2016.21.1.078
While most AUV researches have concerned about single hydrofoil, practical AUV's are generally operated with multiple hydrofoils. Double hydrofoil study attempts to evaluate thrust and efficiency with various flapping motions, and carries out design optimization using parametric analysis. Flow patterns such as vortex shedding and wake-body interaction are carefully investigated during design variable sensitivity analysis. The purpose of this design optimization is to find out the optimal motion that yields maximum thrust and efficiency. The design optimization employes several techniques such as table of orthogonal arrays, Kriging method, ANOVA analysis and MGA. Throughout this research, it is possible to find the optimal values of heaving ratio, heaving shift and pitch shift: Heaving ratio 0.950, heaving shift
and pitch shift
are found to be optimal values in double hydrofoil motions. Thrust and efficiency are 16.7% and 35.1% higher than existing AUV that did not consider nonlinear dependency of motion parameters. This results may offer an effective framework that is applicable to various AUV motion analyses and designs.
COMPUTATIONAL ANALYSIS OF THERMAL FLOW WITH VARYING THE DIAMETER AND THE NUMBER OF TUBES IN PULSATING HEAT PIPES
Han, S.H. ; Choi, J.W. ; Kim, S.C. ;
Journal of computational fluids engineering, volume 21, issue 1, 2016, Pages 86~93
DOI : 10.6112/kscfe.2016.21.1.086
In this paper, heat transfer characteristics of pulsating heat pipes are investigated with the diameter and the number of tubes through the computational analysis of thermal flow. The numerical simulation includes the phase change precess with VOF model using OpenFOAM software. The numerical code is modified for the phase change to occur with saturation temperature. The numerical results are compared with the previous ones to validate the present code. The resonable results have been obtained based on the mass transfer time relaxation parameter considering the density ratio. When the ratio of length to diameter and the number of tubes are on the decrease, the thermal resistances also tends to decrease in the pulsating heat pipes. These numerical results will supply the base line data to design and to manufacture the pulsating heat pipe.
ACCURACY IMPROVEMENT OF THE BLEED BOUNDARY CONDITION WITH THE EFFECTS OF POROSITY VARIATIONS AND EXPANSION WAVES
Kim, G. ; Choe, Y. ; Kim, C. ;
Journal of computational fluids engineering, volume 21, issue 1, 2016, Pages 94~102
DOI : 10.6112/kscfe.2016.21.1.094
The present paper deals with accuracy improvement of a bleed boundary condition model used to improve the performance of supersonic inlets. In order to accurately predict the amount of bleed mass flow rates, this study performs a scaling of sonic flow coefficient data for 90-degree bleed holes in consideration of Prandtl-Meyer expansion theory. Furthermore, it is assumed that porosity varies with stream-wise location of the porous bleed plate to accurately predict downstream boundary layer profiles. The bleed boundary condition model is demonstrated through Computational Fluid Dynamics(CFD) simulations of bleed flows on a flat plate with/without an oblique shock. As a result, the bleed model shows the improved accuracy of bleed mass rates and downstream boundary layer profiles.
DESIGN OF A CENTRIFUGAL BLOOD PUMP FOR ECMO DEVICE THROUGH NUMERICAL ANALYSES
Choi, S. ; Hur, N. ; Moshfeghi, M. ; Kang, S. ; Kim, W. ; Kang, S.H. ;
Journal of computational fluids engineering, volume 21, issue 1, 2016, Pages 103~109
DOI : 10.6112/kscfe.2016.21.1.103
With the rapid increase in the number of patients with cardiopulmonary diseases, more cardiopulmonary circulatory assist devices are also needed. These devices can be employed when heart and/or lung function poorly. Due to the critical role they take, these devices have to be designed optimally from both mechanical and biomechanical aspects. This paper presents the CFD results of a baseline model of a centrifugal blood pump for the ECMO condition. The details of flow characteristics of the baseline model together with the performance curves and the modified index of hemolysis(MIH) are investigated. Then, the geometry of baseline impeller and the volute are modified in order to improve the biomechanical performance and reduce the MIH value. The numerical simulations of two cases represent that when impeller radius and prime volume decrease the MIH value also decreases. In addition, the modified geometry shows more uniform pressure distribution inside the volute. The findings provide valuable information for further modification and improvement of centrifugal blood pumps from both mechanical and biomechanical aspects.
CHARACTERISTICS OF INTERFACE BETWEEN TWO-PHASE FLUIDS FLOW IN A FURNACE WITH POROUS MEDIUM
Park, G.M. ; Lee, D.J. ; Lee, J.H. ; Yoon, H.S. ;
Journal of computational fluids engineering, volume 21, issue 1, 2016, Pages 110~116
DOI : 10.6112/kscfe.2016.21.1.110
The present study numerically investigated the deformation of the interface of two-phase fluids flow in a blast furnace. To simulate three-dimensional(3D) incompressible viscous two-phase flow in the furnace filled with the air and molten iron, the volume of fluid(VOF) method based on the finite volume method has been utilized. In addition, the porous medium with the porosity has been considered as the bed of the particles such as cokes and char etc. For the comparison, the single phase flow and the two-phase flow without the porosity have been simulated. The two-phase flow without porosity condition revealed the smooth parabolic profile of the free surface near the outlet. However, the free surface under the porosity condition formed the viscous finger when the free surface was close to the outlet. This viscous finger accelerated the velocity of the free surface falling and the outflow velocity of the fluids near the outlet.