• Title/Summary/Keyword: Axi-Symmetric flow

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Motion of a Horizontal Vortex Under a Background Rotation (배경회전 하의 수평 보텍스의 거동)

  • Suh Yong Kweon;Yeo Chang-Ho
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.10 s.241
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    • pp.1101-1110
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    • 2005
  • In this paper we present the numerical results of the behavior of the horizontal vortex generated by ejecting a liquid vertically upward from an orifice into the bulk fluid above the orifice. The numerical calculation has been performed for the axi-symmetric Navier-Stokes equation. A simple flow-visualization experiment was also conducted to qualitatively verify the numerical solutions. Three cases of the flow configurations studied in this paper are; firstly, the vortex was generated without any background rotation, secondly, the vortex was made under a full background rotation, and thirdly, the vortex was made during the spin-up process such that only the region adjacent to the side wall was set into motion viewed in the inertial frame of reference. It was shown that the swirl flow at the inlet boundary affects considerably the formation and development of the vortex for the second case. In the third case, it was remarkable to see that the vortex cannot penetrate into the region near to the side wall of the tank, because of the strong swirl flow and corresponding high pressure gradient in the region.

Numerical Simulation of In-Cylinder Flow for the Axi-symmetric Model Engine by Low Reynolds Number k-ε Turbulence Model (저레이놀즈수 k-ε 난류모형에 의한 축대칭 모형기관 실린더내 유동의 수치해석)

  • Kim, W.K.;Choi, Y.D.
    • Transactions of the Korean Society of Automotive Engineers
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    • v.2 no.1
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    • pp.38-50
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    • 1994
  • To improve the efficiency of internal combustion engines, it is necessary to understand mixed air-fuel in-cylinder flow processes accurately at intake and compression strokes. There is experimental and numerical methods to analyse in-cylinder flow process. In numerical method, standard $k-{\varepsilon}$ model with wall function was mostly adopted in in-cylinder flow process. But this type model was not efficiently predicted in the near wall region. Therefore in the present study, low Reynolds number $k-{\varepsilon}$ model was adopted near the cylinder wall and standard $k-{\varepsilon}$ model in other region. Also QUICK scheme was used for convective difference scheme. This study takes axisymmetric reciprocating model engine motored at 200rpm with a centrally located valve, incorporated 60 degree seat angie, and flat piston surface excluding inlet port. Because in-cylinder flow processes are undergoing unsteady and compressible, averaged cylinder pressure and inlet velocity at arbitrary crank angle are determined from thermodynamic analytic method and incylinder states at that crank angle are iteratively determined from the numerical analytic method.

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Analysis of Unstable Shock-Induced Combustion over Wedges and Conical Bodies (쐐기 및 원추 주위의 불안정한 충격파 유도연소 해석)

  • Jeong-Yeol Choi
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2003.05a
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    • pp.32-33
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    • 2003
  • Mechanism of a periodic oscillation of shock-induced combustion over a two- dimensional wedges and axi-symmetric cones were investigated through a series of numerical simulations at off-attaching condition of oblique detonation waves(ODW). A same computational domain over 40 degree half-angle was considered for two-dimensional and axi-symmetric shock-induced combustion phenomena. For two-dimensional shock-induced combustion, a 2H2+02+17N2 mixture was considered at Mach number was 5.85with initial temperature 292 K and initial pressureof 12 KPa. The Rankine-Hugoniot relation has solution of attached waves at this condition. For axi-symmetric shock-induced combustion, a H2+2O2+2Ar mixture was considered at Mach number was 5.0 with initial temperature 288 K and initial pressure of 200 mmHg. The flow conditions were based on the conditions of similar experiments and numerical studies.[1, 3]Numerical simulation was carried out with a compressible fluid dynamics code with a detailed hydrogen-oxygen combustion mechanism.[4, 5] A series of calculations were carried out by changing the fluid dynamic time scale. The length wedge is varied as a simplest way of changing the fluid dynamic time scale. Result reveals that there is a chemical kinetic limit of the detached overdriven detonation wave, in addition to the theoretical limit predicted by Rankine-Hugoniot theory with equilibrium chemistry. At the off-attaching condition of ODW the shock and reaction waves still attach at a wedge as a periodically oscillating oblique shock-induced combustion, if the Rankine-Hugoniot limit of detachment isbut the chemical kinetic limit is not.Mechanism of the periodic oscillation is considered as interactions between shock and reaction waves coupled with chemical kinetic effects. There were various regimes of the periodicmotion depending on the fluid dynamic time scales. The difference between the two-dimensional and axi-symmetric simulations were distinct because the flow path is parallel and uniform behind the oblique shock waves, but is not behind the conical shock waves. The shock-induced combustion behind the conical shockwaves showed much more violent and irregular characteristics.From the investigation of characteristic chemical time, condition of the periodic instability is identified as follows; at the detaching condition of Rankine-Hugoniot theory, (1) flow residence time is smaller than the chemical characteristic time, behind the detached shock wave with heat addition, (2) flow residence time should be greater than the chemical characteristic time, behind an oblique shock wave without heat addition.

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Three-dimensional Effects of an Axi-symmetric Pintle Nozzle (축대칭 핀틀노즐의 3차원 효과 분석)

  • Lee, Gang-Min;Sung, Hong-Gye
    • Journal of the Korean Society of Propulsion Engineers
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    • v.22 no.6
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    • pp.47-55
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    • 2018
  • In order to determine whether three-dimensional effects exist in a pintle nozzle of axisymmetric shape, a three-dimensional numerical analysis was performed. The compressibility correction was implemented with the k-${\omega}$ SST turbulence model to predict the complex flow separation transition in acceptable accuracy. Recirculation zones were observed at both the front end and rear faces of the pintle, and the flow through the pintle nozzle conveyed complex shock wave structures. Three-dimensional effects that resulted from the reasonable flow separation location were noted, and a trace of the transient pressure increase was observed, mismatched by a two-dimensional axi-symmetric analysis.

Study on the unidirectional compaction of terminal cables in the CICC joint

  • 남현일;이호진;박재학;홍계원
    • Progress in Superconductivity
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    • v.3 no.2
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    • pp.218-223
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    • 2002
  • The void volume fraction of cables is one of the effective parameters to characterize the joints of superconducting magnet. Because electrical resistance and cooling stability in the CICC (Cable-in-Conduit Conductors) joint are governed by the void volume fraction, it should be controlled constantly in the termination of cable. The change of cross-section shape in the cable was fecund during the unidirectional compaction of terminal sleeve. The non-uniform thickness of the sleeve after compaction is expected because the loading is not taxi-symmetric, and the plastic flow is also not axi-symmetric. The CICC was compacted from 45% void volume fraction to 15% by using two-piece compaction jig, which could be pressed mini-directionally. Commercial code, ABAQUS, was used to analyze the plastic flow in the sleeve during the unidirectional compaction. The increment of radius of curvature of compaction jig could minimize the change of the deformed shape of cables. The calculated results were agreed with the experimental observations.

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SIMULATION OF CAVITATING FLOW PAST CYLINDERS WITH STRONG SIDE-FLOW (측류유동을 고려한 실린더 주위의 캐비테이션 유동 현상 해석)

  • Lee, B.W.;Park, W.G.;Lee, K.C.
    • Journal of computational fluids engineering
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    • v.14 no.4
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    • pp.78-85
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    • 2009
  • Cavitating flow simulation is of practical importance for many engineering systems, such as marine propellers, pump impellers, nozzles, injectors, torpedoes, etc. The present work has focused on the simulation of cavitating flow past cylinders with strong side flows. The governing equation is the Navier-Stokes equation based on the homogeneous mixture model. The momentum and energy equation is in the mixture phase while the continuity equation is solved liquid and vapor phase, separately. An implicit dual time and preconditioning method are employed for computational analysis. For the code validation, the results from the present solver have been compared with experiments and other numerical results. A fairly good agreement with the experimental data and other numerical results have been obtained. After the code validation, the strong side flow was applied to include the wake flow effects of the submarine or ocean tide.

Numerical simulation of thermo-fluid flow in the blast furnace (고로내 열유동 현상의 수치해석 사례(I))

  • Jin, Hong-jong;Choi, Sang-Min
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2038-2043
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    • 2007
  • Analysis of the internal state of the blast furnace is needed to predict and control the operating condition. Especially, it is important to develop modeling of blast furnace for predicting cohesive zone because shape of cohesive zone influences on overall operating condition of blast furnace such as gas flow, temperature distribution and chemical reactions. Because many previous blast furnace models assumed cohesive zone to be fixed, they can't evaluate change of cohesive zone shape by operation condition such as PCR, blast condition and production rate. In this study, an axi-symmetric 2-dimensional steady state model is proposed to simulate blast furnace process using the general purpose-simulation code. And Porous media is assumed for the gas flow and the potential flow for the solid flow. Velocity, pressure and temperature distribution for gas and solid are displayed as the simulation results. The cohesive zones are figured in 3 different operating conditions.

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Formability of Flow Turning Process (플로우 터닝 공정에서의 성형성 연구)

  • Choi S.;Kim S. S.;Na K. H.;Cha D. J.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2001.10a
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    • pp.195-199
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    • 2001
  • The flow turning process, an incremental forming process, is a cost-effective forming method for axi-symmetric intricate parts to net shape. However, the flow turning process shows a fairly complicated deformation, it is very difficult to obtain satisfactory results. Therefore extensive experimental and analytical research has not been carried out. In this study, an fundamental experiment was conducted to improve productivity with process parameters such as tool path, angle of roller holder($\alpha$), feed rate(v ) and comer radius of forming roller(Rr). These factors were selected as variables in the experiment because they were most likely expected to have an effect on spring back. The clearance was controlled in order to achieve the precision product which is comparable to deep drawing one. And also thickness and diameter distributions of a multistage cup obtained by flow turning process were observed and compared with those of a commercial product produced by conventional deep drawing.

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CFD Model of the Base Flow on Axi-symmetric Nacelle Using Singularities (축대칭 나셀에서 특이점을 이용한 베이스 유동의 전산해석적인 모델)

  • Baik Doo Sung;Han Young Chool
    • Journal of computational fluids engineering
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    • v.6 no.2
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    • pp.1-8
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    • 2001
  • Despite the massive effort which has been given to the analysis of the base flows, one commonly occurring case seems to be overlooked. This is for base (rearward facing surface) which is between a subsonic flow and supersonic flow. Potential flows of the air and gas streams are computed for the flow past a separated wake. Then a viscous jet mixing is superimposed on this inviscid solution. Conservation of mass, momentum and energy is achieved by multiple iterations. Despite the iterations, the wake flow field is computed with modest computer requirements.

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A Numerical Study on the Performance of a Two-Stage Ejector-Diffuser System

  • Kong, Fanshi;Kim, Heuy Dong
    • Journal of Advanced Marine Engineering and Technology
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    • v.39 no.5
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    • pp.548-553
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    • 2015
  • The conventional ejector-diffuser system makes use of high pressure primary stream to propel the secondary stream through pure shear action for the purposes of transport or compression of fluid. It has been widely used in many industrial applications such as seawater desalination, solar refrigeration, marine engineering, etc. The present study is performed numerically to study the performance of a two-stage ejector-diffuser system. The detailed flow phenomenon of the ejector-diffuser system has been critically predicted by means of the numerical approach using compressible Reynolds averaged Navier-Stokes (RANS) equations. The axi-symmetric supersonic ejector-diffuser flow has been solved by a fully implicit finite volume scheme with a two-equation k-omega turbulence model. The numerical results are validated with existing experimental data. Detailed flow physics and their contributions on ejector performance are detected to compare both single-stage and two-stage ejectors. The performance improvement on the ejector-diffuser system is discussed in terms of the mass flux ratio and the coefficient of power.