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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of computational fluids engineering
Journal Basic Information
Journal DOI :
Korea Society of Computational Fluids Engineering
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Volume & Issues
Volume 20, Issue 4 - Dec 2015
Volume 20, Issue 3 - Sep 2015
Volume 20, Issue 2 - Jun 2015
Volume 20, Issue 1 - Mar 2015
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CAVITATION ANALYSIS IN A CENTRIFUGAL PUMP USING VOF METHOD
Lee, W.J. ; Lee, J.H. ; Hur, N. ; Yoon, I.S. ;
Journal of computational fluids engineering, volume 20, issue 4, 2015, Pages 1~6
DOI : 10.6112/kscfe.2015.20.4.001
Centrifugal pumps consume considerable amount of energy in various industrial applications. Therefore, improvement of the efficiency of these machines has become a major challenge. Cavitation is a phenomenon which decreases the pump efficiency and even causes structural demage. Hence, the goal of this paper is to investigate the cavitation problem in the single-stage and double-stage centrifugal pumps. The Volume of Fraction (VOF) method has been used for the numerical simulations together with Rayliegh-Plesset model for the gas-liquid two-phase flow inside the pump. In order to capture the turbulent phenomena, the standard k-
turbulence model has been adopted, and the simulations have been done as unsteady cases. In addition, the motion of the rotating parts has been simulated using Multi Reference Frame(MRF) method. The results are presented and compared in terms of hydraulic head and NPSH for both the single-stage and double-stage pumps. The H-Q curves show the effects of cavitation on decreasing the pumps performances.
A PARAMETRIC STUDY OF CONICAL FRUSTUM GEOMETRY FOR IMPROVEMENT OF COOLING PERFORMANCE OF VORTEX TUBE
Koo, H.B. ; Park, J.Y. ; Sohn, D.Y. ; Choi, Y.H. ;
Journal of computational fluids engineering, volume 20, issue 4, 2015, Pages 7~13
DOI : 10.6112/kscfe.2015.20.4.007
Vortex tube is a thermal static device that separates compressed air into hot and cold streams. In general, the cooling efficiency of vortex tubes is lower than that of traditional air conditioning equipment and vortex tubes are mainly used for industrial spot cooling applications because of their quick responses. In this study, conical frustums are employed in the nozzle chamber to improve the cooling performance. Conical frustums can be used to decrease the ineffective mass fraction that directly passes through the cold exit without energy separation. The shape optimization of conical frustums has been performed using full factorial design. It is found that the height of frustums has the largest main effects on the cooling performance. Computational results show that the cooling performance can be increased by about 10% within the considered range of the design parameters. This is because the ineffective mass fraction toward the cold exit is decreased by about 20%.
NATURAL CIRCULATION ANALYSIS CONSIDERING VARIABLE FLUID PROPERTIES WITH THE CUPID CODE
Lee, S.J. ; Park, I.K. ; Yoon, H.Y. ; Kim, J. ;
Journal of computational fluids engineering, volume 20, issue 4, 2015, Pages 14~20
DOI : 10.6112/kscfe.2015.20.4.014
Without electirc power to cool down the hot reactor core, passive systems utilizing natural circulation are becoming a big specialty of recent neculear systems after the severe accident in Fukusima. When we consider the natural circulation in a pool, thermal mixing phenomena may start from single phase circulation and can continue to two phase condition. Since the CUPID code, which has been developed for two-phase flow analysis, can deal with the phase transition phenomena, the CUPID would be pertinent to natural convection problems in single- and two-phase conditions. Thus, the CUPID should be validated against single- and two-phase natural circulation phenomena. For the first step of the validation process, this study is focused on the validation of single-phase natural circulation. Moreover, the CUPID code solves the fluid properties by the relationship to pressure and temperature from the steam table considering non-condensable gas effects, so that the effects from variable properties are included. Simple square thermal cavity problems are tested for laminar and turbulent conditions against numerical and experimental data. Throughout the investigation, it is found that the variable properties can affect the flow field in laminar condition, but the effect becomes weak in turbulence condition, and the CUPID code implementing steam table is capable of analyzing single phase natural circualtion phenomena.
COMPUTATION OF FLOW AROUND A SHIP USING A SURFACE INTERPOLATED FROM STATION LINES
Kim, Hyun-Sik ; Shin, Sangmook ;
Journal of computational fluids engineering, volume 20, issue 4, 2015, Pages 21~27
DOI : 10.6112/kscfe.2015.20.4.021
Flow field around the KRISO 3600TEU container ship is computed using a surface generated based on interpolations of station lines, which are given in a body plan of the ship, without using any CAD program. An interpolation method is suggested based on inscribed circles to generate curves between two neighboring station lines. The interpolated surface is saved in a STL format to use the snappyHexMesh utility of the openfoam. Computed resistance of the ship is compared with experimental and other computational results and the effects of the interpolation of neighboring station lines on the computed resistance are investigated. The suggested method is applied to calculate the flow field around a submarine with appendages. The surface triangulations for the hull and the appendages are generated without consideration of each other, then those surface triangulations are simply combined to provide a grid generator with the body boundary. The junctures of the hull and the appendages are identified automatically during the grid generation procedure. Tip vortex is captured, which travels downstream from the tip of the appendages.
BARAM: VIRTUAL WIND-TUNNEL SYSTEM FOR CFD SIMULATION
Kim, Min Ah ; Lee, Joong-Youn ; Gu, Gibeom ; Her, Young-Ju ; Lee, Sehoon ; Park, Soo Hyung ; Kim, Kyu Hong ; Cho, Kumwon ;
Journal of computational fluids engineering, volume 20, issue 4, 2015, Pages 28~35
DOI : 10.6112/kscfe.2015.20.4.028
BARAM system that means 'wind' in Korean has been established as a virtual wind tunnel system for aircraft design. Its aim is to provide researchers with easy-to-use, production-level environment for all stages of CFD simulation. To cope with this goal an integrated environment with a set of CFD solvers is developed and coupled with an highly-efficient visualization software. BARAM has three improvements comparing with previous CFD simulation environments. First, it provides a new automatic mesh generation method for structured and unstructured grid. Second, it also provides real-time visualization for massive CFD data set. Third, it includes more high-fidelity CFD solvers than commercial solvers.
TRANSITIONAL FLOW ANALYSIS OVER DOUBLE COMPRESSION RAMP WITH NOSE BLUNTNESS IN SUPERSONIC FLOW
Shin, Ho Cheol ; Sa, Jeong Hwan ; Park, Soo Hyung ; Byun, Yung Hwan ;
Journal of computational fluids engineering, volume 20, issue 4, 2015, Pages 36~43
DOI : 10.6112/kscfe.2015.20.4.036
Accurate prediction of supersonic transition is required for the heat transfer estimation over supersonic double compression ramp flows. Correlation-based transition models were assessed for a supersonic double ramp problem. Numerical results were compared with experimental data from RWTH Aachen University. A parametric study on the nose bluntness was performed using a selected transition model. As the nose bluntness increases, the boundary layer thickness is increased and the triple point of shock interactions moves downstream. The peak magnitude of the heat transfer is consequently decreased with the nose bluntness.
IMPROVEMENT OF FLOW SIMULATIONS METHOD WITH MULTI-RESOLUTION ANALYSIS BY BOUNDARY TREATMENT
Kang, H.M. ;
Journal of computational fluids engineering, volume 20, issue 4, 2015, Pages 44~50
DOI : 10.6112/kscfe.2015.20.4.044
The computational efficiency of flow simulations with Multi-resolution analysis (MRA) was enhanced via the boundary treatment of the computational domain. In MRA, an adaptive dataset to a solution is constructed through data decomposition with interpolating polynomial and thresholding. During the decomposition process, the basis points of interpolation should exceed the boundary of the computational domain. In order to resolve this problem, the weight coefficients of interpolating polynomial were adjusted near the boundaries. By this boundary treatment, the computational efficiency of MRA was enhanced while the numerical accuracy of a solution was unchanged. This modified MRA was applied to two-dimensional steady Euler equations and the enhancement of computational efficiency and the maintenance of numerical accuracy were assessed.
NUMERICAL SIMULATION OF FLOW PAST A SQUARE CYLINDER SUBMERGED UNDER THE FREE SURFACE
Ahn, Hyungsu ; Yang, Kyung-Soo ; Park, Doohyun ;
Journal of computational fluids engineering, volume 20, issue 4, 2015, Pages 51~57
DOI : 10.6112/kscfe.2015.20.4.051
In the present study, two-dimensional numerical investigation of flow past a square cylinder beneath the free surface has been performed to identify the effects of presence of the free surface. An immersed boundary method was adopted for implementation of the cylinder cross-section in a Cartesian grid system. Also, a level-set method was used to capture the interface of two fluids. To prevent transition to three-dimensional flow, Reynolds number chosen for this simulation was 150. The cases for Froude number 0.2 and gap ratio(h/D) between 0.25 and 5.00 were examined. At the specific Reynolds number, we study the effects of gap ratio on flow characteristics around a square cylinder by computing flow fields, force coefficients and Strouhal number.
HOMOCLINIC ORBITS IN TRANSITIONAL PLANE COUETTE FLOW
Lustro, Julius Rhoan T. ; Kawahara, Genta ; van Veen, Lennaert ; Shimizu, Masaki ;
Journal of computational fluids engineering, volume 20, issue 4, 2015, Pages 58~62
DOI : 10.6112/kscfe.2015.20.4.058
Recent studies on wall-bounded shear flow have emphasized the significance of the stable manifold of simple nonlinear invariant solutions to the Navier-Stokes equation in the formation of the boundary between the laminar and turbulent regions in state space. In this paper we present newly discovered homoclinic orbits of the Kawahara and Kida(2001) periodic solution in plane Couette flow. We show that as the Reynolds number decreases a pair of homoclinic orbits move closer to each other until they disappear to exhibit homoclinic tangency.
STUDY ON A EFFECTIVE THERMAL CONDUCTIVITY OF THE CFRP COMPOSITE STRUCTURE BY A SIMPLIFIED MODEL
Kim, D.G. ; Han, K.I. ; Choi, J.H. ; Lee, J.J. ; Kim, T.K. ;
Journal of computational fluids engineering, volume 20, issue 4, 2015, Pages 63~69
DOI : 10.6112/kscfe.2015.20.4.063
The thermal balance test in vacuum chamber for satellite structures is an essential step in the process of satellite development. However, it is technically and economically difficult to fully replicate the space environment by using the vacuum chamber. To overcome these limitations, the thermal analysis through a computer simulation technique has been conducted. The CFRP composite material has attracted attention as satellite structures since it has advantages of excellent mechanical properties and light weight. However, the nonuniform nature of the thermal conductivity of the CFRP structure should be noted at the step of thermal analysis of the satellite. Two different approaches are studied for the thermal analyses; a detailed numerical modeling and a simplified model expressed by an effective thermal conductivity. In this paper, the effective thermal conductivities of the CFRP composite structures are extracted from the detailed numerical results to provide a practical thermal design data for the satellite fabricated with the CFRP composite structure. Calculation results of the surface temperature and the thermal conductivities along x, y, z directions show fairly good agreements between the detailed modeling and the simplified model for all the cases studied here.
INVESTIGATION OF THE OPERATIONAL PRINCIPLE AND PARAMETRIC STUDY ON A DRY PASTE SEPARATOR EQUIPED WITH A ROTOR - I. THEORETICAL STUDY
Park, S.U. ; Kang, Y.S. ; Kang, S. ; Suh, Y.K. ;
Journal of computational fluids engineering, volume 20, issue 4, 2015, Pages 70~80
DOI : 10.6112/kscfe.2015.20.4.070
Construction waste is known to include a large part of coarse and fine aggregates, which can be recirculated in the industry. Separating those aggregates economically from the waste has been thus considered to be one of the most important issues in this field. In particular, paste mixed in the waste causes significant complain from the inhabitants living near the place where waste-processing equipments are built and operated. In this study, we investigate the operational principle of a newly developed paste separator by using theoretical (in this first part) and CFD (in the second part) analysis. The separator consists of a rotor which turned out to play a significant role in separating those pastes from the aggregates. Under suitable assumptions regarding the air flow velocity as well as the particle velocity, we show that particles can be stagnant at the outlet of the roto channel for a wide range of parameter values, which allow the particles to get enough time to settle down via the gravitation. We also demonstrate such phenomenon by using a simple numerical simulation.
INVESTIGATION OF THE OPERATIONAL PRINCIPLE AND PARAMETRIC STUDY ON A DRY PASTE SEPARATOR EQUIPED WITH A ROTOR -II. CFD ANALYSIS
Park, S.U. ; Kang, Y.S. ; Kang, S. ; Suh, Y.K. ;
Journal of computational fluids engineering, volume 20, issue 4, 2015, Pages 81~92
DOI : 10.6112/kscfe.2015.20.4.081
Construction waste mainly consists of concrete aggregates of various size. Improper handling of concrete waste would be a major environmental problem whereas its recycling would be both economically useful and environmentally friendly. Bigger concrete aggregates are crushed and converted to medium and fine particles to make them recyclable. An apparatus to separate the concrete aggregates by their size is thus needed for their effective recycling. In this work, segregation of concrete particles in air flows from a newly designed rotary separator having three stages of blades is simulated using a commercial software, ANSYS-CFX. Both 2-D and 3-D models with 360, 240 and 180 blades in each stage are considered. Fundamental mechanism of separation of particles(pase) and the effect of design parameters such as particle size, rotor speed, air flow rate etc. on the performance of the separator are investigated. Critical size of particles that can be separated by the developed separator is also presented in this work. Simulation results are overall in good agreement with data predicted from the theoretical model previously reported in the companion paper.
NUMERICAL ANALYSIS OF THE FLOW AROUND THE HULL AND THE PROPELLER OF A SHIP ADVANCING IN SHALLOW WATER
Park, I.R. ;
Journal of computational fluids engineering, volume 20, issue 4, 2015, Pages 93~101
DOI : 10.6112/kscfe.2015.20.4.093
This paper provides numerical results of the simulation for the flow around the hull and the propeller of KCS model ship advancing in shallow water conditions. A finite volume method is used to solve the unsteady Reynolds averaged Navier-Stokes(RANS) equations, where the wave-making problem is solved by using a volume-of-fluid(VOF) method. The wave formed near the hull surface in shallow water conditions shows a deep trough dominant pattern that causes the loss of buoyancy followed by hull squat. The flow past the hull increases as the depth of water decreases. However, the axial flow velocity around the stern shows a reduction in magnitude by the effect of shallow water accompanied by the hull-propeller interaction. As a results, the thrust and torque coefficient increase about 8.3% and 6.2%, respectively for a depth of h/T=3.0 corresponding to a depth Froude number of
. The resistance coefficient increases about 11.6% at this Froude number condition.
HONEYCOMB LABYRINTH SEAL LEAKAGE CHARACTERISTIC ANALYSIS WITH ACTUAL OPERATING CONDITIONS ON THE COMPRESSOR OF GAS TURBINE
Lim, S.B. ; Kim, M.K. ; Kang, Y.H. ; Park, W.G. ;
Journal of computational fluids engineering, volume 20, issue 4, 2015, Pages 102~108
DOI : 10.6112/kscfe.2015.20.4.102
Recently, There are many studies in progress in order to improve the efficiency of the gas turbine. Leakage in losses of the gas turbine account for the largest proportion. Seal is a sealing device to reduce the flow from leaking by the pressure difference inside the turbine. Compressor has another value according to the shape and pressure conditions in each stage. Thus, it is necessary to seal design for boundary conditions in order to minimize leakage. At the actual operating conditions of the compressor, numerical analysis of honeycomb labyrinth seal was performed in accordance with pressure, temperature, rotor speed for CFD. As a result, when the temperature increases, the leakage is decreased. Also, when the pressure increases linearly with increased leakage, and there was no effect of the rotation speed.
STOKES FLOW THROUGH A MICROCHANNEL WITH PROTUBERANCES OF STAGGERED ARRANGEMENT
Son, Jeong Su ; Jeong, Jae-Tack ;
Journal of computational fluids engineering, volume 20, issue 4, 2015, Pages 109~115
DOI : 10.6112/kscfe.2015.20.4.109
In this study, the Stokes flow in the microchannel is analysed where the semicircular protuberances with constant spacing are attached on the upper and lower walls with staggered arrangement. For the low Reynolds number flow in microchannel, Stokes approximation is used and the periodicity and symmetry of the flow are considered to determine the stream function and pressure distribution in the flow field by using the method of least squared error. As results, the streamline patterns and pressure distributions in the flow field are shown for some specific values of the size and spacing of the protuberances, and shear stress distributions on the surface of semicircular protuberances are plotted. Especially, for an important physical property, the average pressure gradient along the microchannel is obtained and compared with that for the case of in-phase arrangement of the upper and lower protuberances. And, for the small clearance between the protuberances of upper and lower walls or between the protuberances and the opposite wall, the average pressure gradient is derived from the lubrication theory and compared with that of the present study.