• Journal of computational fluids engineering
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• v.11 no.2 s.33
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• pp.1-7
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• 2006

An unstructured overset mesh method has been developed for the simulation of unsteady viscous flow fields around multiple bodies in relative motion. For this purpose, a robust and fast search technique is proposed for both triangle and high-aspect ratio quadrilateral cell elements. The interpolation boundary is defined for data communication between grid systems and an interpolation method is suggested for viscous and inviscid cell elements. This method has been applied to calculate the flow fields around 2-D airfoils involving relative motion. Validations were made by comparing the predicted results with those of experiments or other numerical results. It was demonstrated that the present method is efficient and robust for the prediction of unsteady time-accurate flow fields involving multiple bodies in relative motion.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.3
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• pp.233-240
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• 2017

The flowfield around transonic wing-body configuration was simulated using in-house CFD code and compared with the experimental data to understand the influence of several features of CFD(Computational Fluid Dynamics) ; grid dependency, turbulence models, spatial discretization, and viscosity. The wing-body configuration consists of a simple planform RAE Wing 'A' with an RAE 101 airfoil section and an axisymmetric body. The in-house CFD code is a compressible Euler/Navier-Stokes solver based on unstructured grid. For the turbulence model, the $k-{\omega}$ model, the Spalart-Allmaras model, and the $k-{\omega}$ SST model were applied. For the spatial discretization method, the central differencing scheme with Jameson's artificial viscosity and Roe's upwind differencing scheme were applied. The results calculated were generally in good agreement with experimental data. However, it was shown that the pressure distribution and shock-wave position were slightly affected by the turbulence models and the spatial discretization methods. It was known that the turbulent viscous effect should be considered in order to predict the accurate shock wave position.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.1
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• pp.11-23
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• 1989

A computer code has been developed to simulate three-dimensional viscous flows over a ship-stern. Semi-elliptic forms of Reynolds equations are adopted and numerically generated body-fitted coordinate systems are used to resolve complex geometries of the ship-hull. A standard form of $k-\varepsilon$ turbulence model is adopted for evaluation of the Reynolds stresses. Turbulent flows on a model with 3:1 elliptic sections and the SSPA-720 container ship model are predicted by using the code. Calculated pressure distributions of hull-surfaces and mean velocity distributions are generally in good agreements with measured values in wind-tunnels. But turbulent kinetic energies tend to be over-estimated near the stern in comparison with measured data.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.3
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• pp.8-17
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• 2002

In this paper, the computational analysis of open-water characteristics for three model propellers(P4119, P4842 and 3 podded propeller of KRISO) is done by using a viscous-flow method based on Reynolds-Averaged Navier-Stokes equations. The results are presented for open-water performances, blade-section pressures, and circumferentially-averaged velocity profiles for the all three propeller models. Overall close agreements with available experimental data are shown. However, some discrepancies are also found in the pressure near the leading edge of the propeller blade and the open-water performance of the podded propellers.

• Journal of Navigation and Port Research
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• v.37 no.1
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• pp.1-7
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• 2013

In this paper the developed prediction technique of wave-making resistance performance for a ship attached with a vertical blade had been verified. Numerical analysis program as a prediction technique had been developed using the Rankine source panel method and the vortex lattice method(VLM). The nonlinearity of the free surface conditions was fully taken into account using the iterative method and the trim and the sinkage of the ship were also considered in the numerical analysis program. Panel cutting method was applied to get hull surface panels. Numerical computations were carried out for a 4000TEU container carrier and the vertical blade was attached 6 different locations astern. To investigate the validity of the numerical analysis program the commercial viscous flow field analysis program FLUENT was used to obtain the viscous flow field around the ship and the model test was performed. The model test results were compared with the numerical analysis results.

• The Journal of the Acoustical Society of Korea
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• v.33 no.6
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• pp.358-365
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• 2014

When a ship propeller having wing type sections rotates at high speed underwater, local pressure on the blade decreases and various types of the cavitation inevitably occur where the local pressure falls below the vapor pressure. Fundamentally characteristics of the cavitation are determined by the shapes of the blade section and their operating conditions. Underwater noise radiated from a ship propeller is directly connected to the occurrence of the cavitation. In order to design low noise propeller, it is preferentially demanded to figure out key features: how the cavity is generated, developed and collapsed and how the effect of viscosity works in the process. In this study, we first perform inviscid analysis of the partial cavity generated on two dimensional hydrofoil. Secondly, viscous analysis using FLUENT with different turbulence and cavitation models are presented. Results from both approaches are also compared and estimated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.15-20
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• 2005

Two-dimensional incompressible Navier-Stokes flow solver is developed using SIMPLER method to study the unsteady viscous flow physics over two-dimensional ellipses. Unsteady viscous flows over various thickness-to-chord ratios of 0.6, 0.8, 1.0, and 1.2 elliptic cylinders are simulated at different Reynolds numbers of 200, 400, and 1,000. This study is focused on the understanding the effects of Reynolds number and elliptic cylinder thickness on the drag and lift forces. The present numerical solutions are compared with available experimental and numerical results and show a good agreement. Through this study, it is observed that the Reynolds number and the cylinder thickness affect not only the frequency of the force oscillations but also the mean values and the amplitudes of the total drag and lift forces significantly.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.10a
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• pp.487-494
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• 1995

원자력발전소의 안전성 향상을 목적으로 신형원자로 안전주입계통의 축압기 설계에 적용이 고려되고 있는 피동적 유량조절 장치인 vortex 밸브의 유동장을 해석하여 밸브의 특성에 영향을 미치는 주요 인자들을 도출하고 이 인자들의 영향을 분석하였다. 분석 결과 Vortex 밸브의 성능 특성은 수송유량, 제어유량, chamber의 반경, 입구면적, 마찰계수 등의 영향을 받는 것으로 나타났으며 이들 인자 중 chamber의 반경의 영향이 가장 크고 Reynolds수의 영향은 비교적 작은 것으로 파악되었다. 또한 주어진 유동조건에서 제어유량이 작은 경우 점성손실이 vortex 밸브의 유동특성에 미치는 영향이 증대되는 경향을 보였으며 유량이 증가할수록 Reynolds수의 영향은 감소하는 것으로 나타났다.

• 기계와재료
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• v.23 no.3
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• pp.16-29
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• 2011

결정 합금 대비 비정질 합금은 높은 경도를 갖기 때문에 마모 저항성도 좋고 내부 식성 등 환경에 대한 저항성도 월등하며, 또한 과냉된 액상 상태까지 재가열하게 되면 낮은 점성도를 갖게 되므로 복잡한 3차원적인 형상을 가지는 부품을 환경에 대한 저항성, 피로 저항성, 강도 및 경도 등을 모두 고려하여 높은 정밀도를 가지고 제조하는 것이 가능하므로 우수한 물성을 갖는 구조 및 기능성 재료로의 다양한 응용이 타진되고 있다. 이러한 비정질 합금의 변형 거동에 대한 연구는 대부분 유리 천이 온도 이하에서의 전단 및 파단에 이르는 이른바 불균일 변형(Inhomogeneous Deformation) 거동에 대한 이해를 위한 실험 및 해석적 연구에 집중되어 왔다. 반면 상업화의 기반이 되는 고상 기반 2차 정형 성형은 과냉 액상 영역에서의 구조 완화 및 결정화롤 대표되는 미세 구조 제어 균일 변형(Homogeneous Deformation)에 대한 이해 없이는 불가능하므로, 이러한 관점에서 비정질 합금 특유의 점성 유동 특성을 이용한 균일 변형 응용 예시 및 미세구조 변화 연계 해석 기술의 현황을 소개하고자 한다.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.3
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• pp.9-15
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• 2008

Nozzle flow analyses of $30\;ton_f$-class KARI liquid rocket engine for high altitude propulsion are carried out using a chemically frozen and equilibrium flow analysis code developed previously. It is considered that the combined frozen- and shifting- equilibrium analysis is cost-effective regarding the convergence characteristics and modeling uncertainties, though the non-equilibrium analysis is most reliable approach. A dependable performance prediction could be attainable through the present analyses that account for the recombination process and thermal and kinetic energy recovery during the expansion process with viscous effects.