• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.167-173
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• 2010

In this study, flow structure in a three-stage centrifugal compressor for LNG Plant with the refrigerant, Propane, was numerically investigated at the design point of the compressor using a commercial code. Flow characteristics in the passages of impeller and vaneless diffuser were analyzed in detail including velocity vector, Mach number and pressure contours in blade spanwise and meridional plane for each stage. The estimation on the one-dimensional output from the preliminary design and three-dimensional shape of the impeller blade was performed through the flow analysis. The verification for designed compressor was carried out from three-dimensional Navier-Stokes analysis. The results will be used as reference data for a new design of 3-D impeller shape to improve propane refrigerant compressor performance.

• 한국전산유체공학회지
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• 제17권1호
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• pp.29-35
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• 2012

Fluid-Structure Interaction analysis of a circular cylinder surrounded by incompressible turbulent flow is presented. The fluid flow is modeled by incompressible Navier-Stokes equations in conjunction with large-eddy simulation for turbulent vortical flows. The circular cylinder is modeled as elastic continuum described by elasto-dynamic equation of motion. Finite element method based approach is utilized for unified formulation of fluid-structure interaction analysis. The magnitude and frequency of structural response is analysed in comparison to the driving fluid forces.

• 한국소음진동공학회논문집
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• 제14권5호
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• pp.402-409
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• 2004

Numerical analysis of static and dynamic wind effects on civil engineering structures was performed. Long-span suspension bridges are flexible structures that are highly sensitive to the action of the wind. Aerodynamic effect often becomes a governing factor in the design process of bridges and aeroelastic stability boundary becomes a prime criterion which should be confirmed during the structural design stage of bridges because the long-span suspension bridges are prone to the aerodynamic instabilities caused by wind. If the wind velocity exceeds the critical velocity that the bridge can withstand, then the bridge fails due to the phenomenon of flutter. Buffeting caused by turbulence results in structural fatigue, which could lead to the failure of a bridge. Navier-Stokes equations are used for the aeroelastic analysis of bridge girder section. The aeroelastic simulation is carried out to study the aeroelastic stability of bridges using both Computational Fluid Dynamic (CFD) and Computational Structural Dynamic (CSD) schemes.

• 한국소음진동공학회논문집
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• 제24권3호
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• pp.205-212
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• 2014

이 연구에서 현대자동차의 단순실험모델(HSM)에 대한 썬루프 버페팅에 대한 수치해석이 수행되었다. 검증을 위하여 HSM 목부위의 경계층에 대한 속도분포 해석결과를 실험결과와 비교하였다. 썬루프 해석은 두 단계로 이루어졌다. 첫 번째로 난류 RANS 모델을 이용하여 정상상태 해석이 수행되었으며, 해석결과는 CAA++의 입력값으로 사용된다. 두 번째 단계는 유동속도에 대한 1차 최대 압력피크와 버페팅 주파수 해석을 위한 비정상상태 해석이 CAA++에서 이루어졌다. 주파수와 음향압력의 수치해석 결과는 타당한 물리적 현상을 보여주고 있으며, 현대 자동차의 실험결과와 잘 일치하는 결과를 보여주었다.

• 한국수소및신에너지학회논문집
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• 제26권4호
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• pp.386-392
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• 2015

Flow characteristics inside a 10 inch ball valve have been analyzed using three-dimensional numerical analysis and experiments. Continuity and three-dimensional Reynolds-averaged Navier-Stokes equations have been used as governing equations for the numerical analysis. The numerical model has been constructed through the grid dependency test and validation with the results of experiments to ensure reliability and numerical effectiveness. The shear stress transport (SST) model has been used as the turbulence closure. The experimental test-rig has been constructed to measure pressure, temperature and flow rate along the pipeline. Some valve opening angles have been tested to evaluate the flow characteristics inside the ball valve and pipeline. The results show that the rapid pressure variations is observed while the valve opening angle decreases, which caused by flow separation at the downstream of the ball valve.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.343-349
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• 2011

A loosely coupling method is adopted to combine a computational fluid dynamics (CFD) solver and the comprehensive structural dynamics (CSD) code, CAMRAD II, in a systematic manner to correlate the airloads, vortex trajectories, blade motions, and structural loads of the HART I rotor in descending flight condition. A three-dimensional compressible Navier-Stokes solver, KFLOW, using chimera overlapped grids has been used to simulate unsteady flow phenomena over helicopter rotor blades. The number of grids used in the CFD computation is about 24 million for the isolated rotor and about 37.6 million for the rotor-fuselage configuration while keeping the background grid spacing identical as 10% blade chord length. The prediction of blade airloads is compared with the experimental data. The current method predicts reasonably well the BVI phenomena of blade airloads. The vortices generated from the fuselage have an influence on airloads in the 1st and 4th quadrants of rotor disk. It appeared that presence of the pylon cylinder resulted in complex turbulent flow field behind the hub center.

• 한국유체기계학회 논문집
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• 제13권6호
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• pp.42-50
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• 2010

The present analysis deals with a numerical procedure for optimizing the shape of elliptical dimples in a cooling channel. The three-dimensional Reynolds-averaged Navier-Stokes (RANS) analysis is employed in conjunction with the SST model for predictions of the turbulent flow and the heat transfer. Three non-dimensional geometric design variables, such as the ellipse dimple diameter ratio, ratio of the dimple depth to the average diameter, and ratio of the distance between dimples to the pitch are considered in the optimization. Twenty-one experimental points within design space are selected by Latin Hypercube Sampling. Each objective function values at these points are evaluated by RANS analysis and producing optimal point using surrogate model. The linear combination of heat transfer coefficient and friction loss related terms with a weighting factor is defined as the objective function. The results show that the optimized elliptical dimple shape improves considerably the heat transfer performance than the circular dimple shape.

• 한국소음진동공학회논문집
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• 제15권2호
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• pp.148-155
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• 2005

As functional requirement of massive digital information storage devices are on a trend for the higher data transfer rate and lower cost, many different technical efforts are being tested and implemented in the industry. FDB(fluid dynamic bearing) is one of the major breakthroughs in rotor design in terms of TMR(track misregistration) budget. Although FDB analysis based on Reynolds' equation is well established and popularly being used for FDB design especially for the estimation of bearing stiffness, there are obvious limitations in the approach due to the inherent assumptions. A generalized analysis tool employing the full Navier-Stokes equation and the energy balance is to be beneficial for detailed FDB design. In this publication, an efficient geometry modeling method is presented that provides fully integrated inputs for general FVM/FDM(finite volume method/ finite difference method) codes. By virtue of the flexibility of the presented method, many different detailed FDB design and analysis are carried over with ease.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.249-249
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• 2011

전력용 개폐장치인 진공차단기의 차단부가 송배전 시스템에 30 [kA] 정도의 커다란 사고전류가 흐르는 것을 방지하기 위하여 동작될 때 차단부 내부 전극 사이에 25,000 [K] 이상의 아크 플라즈마가 발생하게 된다. 두 전극 사이에 발생된 아크 플라즈마는 약 10 ms~20 ms 동안 지속되다가 교류전원의 전류영점 부근에서 회복된 절연성능으로 인하여 자연스럽게 소멸되지만, 대전류 구간동안 아크 플라즈마의 집중 현상 등에 의하여 전극의 심각한 손상 등이 발생되면 절연성능이 요구된 만큼 회복되지 못하여 사고전류를 차단하지 못하며 시스템에 연결된 기기들에게 심각한 손상을 입히고 정전사고를 일으킨다. 본 연구에서는 전자계-열유동 연성해석기법을 이용한 축자계 진공차단부에서 발생하는 아크 플라즈마의 3차원 수치해석을 통하여 전극의 심각한 손상을 입히는 아크플라즈마의 집중 현상에 관한 축자계의 영향을 고찰하고자 한다. 수치해석을 위한 아크 영역은 양극과 음극의 직경과 같은 직경의 원기둥으로 가정하였고, 전자계 해석으로부터 얻어진 로렌츠 힘과 줄열을 열유동 해석을 위한 Navier-Stokes 방정식의 파라미터로 입력하여 해석을 수행함으로써 전자계와 유체역학적인 영역을 동시에 연계한 순차적 일방향 연성해석 기법을 적용하였다. 컵형 축자계 진공차단부 내 아크영역에서의 로렌츠 힘의 특성과 온도분포에 대하여 수치해석을 수행하였고, 크기가 다른 두 로렌츠 힘에 의하여 양극표면으로 집중되는 온도분포의 크기를 비교함으로써 진공아크 플라즈마의 집중현상에 영향을 미치는 주요 요소를 규명할 수 있었다.

• International Journal of Aeronautical and Space Sciences
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• 제14권3호
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• pp.201-209
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• 2013

Much numerical and experimental research has been done for the flow around an oscillating airfoil. The main research topics are vortex shedding, dynamic stall phenomenon, MAV's lift and thrust generation. Until now, researches mainly have been concentrated on analyzing the wake flow for the variation of frequency and amplitude at a low angle of attack. In this study, wake structures and acoustic wave propagation characteristics were studied for a plunging airfoil at high angle of attack. The governing equations are the Navier-Stokes equation with LES turbulence model. OHOC (Optimized High-Order Compact) scheme and 4th order Runge-Kutta method were used. The Mach number is 0.3, the Reynolds number is, and the angle of attack is from $20^{\circ}$ to $50^{\circ}$. The plunging frequency and the amplitude are from 0.05 to 0.15, and from 0.1 to 0.2, respectively. Due to the high resolution numerical method, wake vortex shedding and pressure wave propagation process, as well as the propagation characteristics of acoustic waves can be simulated. The results of frequency analysis show that the flow has the mixed characteristics of the forced plunging frequency and the vortex shedding frequency at high angle of attack.