• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.2
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• pp.98-107
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• 2002

An experimental and numerical study of aerodynamic charateristics of KSR-III and jet impingement on a deflector during launch has been conducted. To investigate aerodynamic characteristics of KSR-III configuration, wind tunnel tests using 6.4% scale model were performed by 4x4 feet ADD trisonic wind tunnel on the Mach number range of 0.4~3.8. Solutions of Three dimensional Euler equations were also obtained and compared with test result. For the study of KSR-III jet impingement flowfield on a deflector during launch operation, unsteady computation using CFD-FASTRAN was performed.

• Nuclear Engineering and Technology
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• v.26 no.2
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• pp.212-224
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• 1994

A numerical method has been developed for studying the dynamics of a flexible cylinder in a coaxial cylindrical duct, immersed in inviscid flow. The unsteady inviscid fluid-dynamic force acting on the oscillating cylinder has been estimated more rigorously by means of a spectral collocation method without simplification of governing equations. This numerical approach is applicable to the system haying wider annular gap and/or shorter length of cylinder as compared to existing potential theory. The governing equation of the unsteady flow was obtained from Laplace equation. The equation of cylinder motion coupled with the fluid motion was discretized by Galerkin's method, from which the dynamic behaviour of the system has been evaluated. The effect of the length of the cylinder and the annular gap on the critical flour velocity, where the system loses stability by buckling, was investigated. To validate the numerical method, the potential flow theory developed by Hobson based on thin film approximation has been improved. Typical results of the present numerical theory on the dynamics and stability of the system are compared with those of available existing theory and the present approximate results. Good agreement was found between the results. It was also found that a nondimensional critical flow velocity becomes larger as increasing the annular gap and decreasing the length of cylinder.

• Journal of the Korea Institute of Military Science and Technology
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• v.2 no.2
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• pp.279-286
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• 1999

Wall-bounded 유동과 달리 자유 전단 유동은 Hyperbolic Tangent Profile을 가지고 비점성 불안정에 의해 지배된다. 따라서 자유 전단 유동에서 난류로의 천이과정은 비점성 불안정성 이론에 의해 해석되어 진다. 본 연구는 분리판(Splitter plate)에 의해 분리된 속도가 다른 자유 유속의 혼합에 의해 형성되는 혼합층에서 와류병합과정에 대한 속도비의 영향에 대하여 연구한다. 속도비는, R, $ \frac{U_1-U_2}{U_1+U_2}$ 로 정의되며, 여기서 $U_1$은 분리판 위에서의 자유 유속을 그리고 $U_2$ 는 분리판 아래에서의 자유 유속을 나타낸다. 본 연구에서 와류구조의 병합작용을 분석하기 위하여 2차원 비정상 Large-Eddy Simulation 방법을 적용하였다. 속도비의 변화에 따라 혼합층에서 불안정 Wave가 성장하게 되고, 유체는 2차원 와류구조에서 Roll-up한다. 이러한 2차원 와류구조는 주위의 다른 와류구조와 상호작용을 하게 되고 하나의 커다란 와류구조를 형성하는 것을 볼 수 있다. 혼합층에서 와류병합과정은 반복적으로 일어나는 것을 알 수 있었고, 이 결과를 이용하여 혼합층의 성장을 제어할 수 있다.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.1268-1271
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• 2007

트렌치 수로에서 동수압을 고려한 자유수면 흐름을 해석하고 난류 모형의 적용성을 제시하였다. 본 연구에 사용된 지배방정식으로 비정상 상태의 비압축성 유체에 대한 연속방정식과 비점성 Navier-Stokes 방정식을 사용하였다. 난류완결문제를 해결하기 위해서 $\kappa-\varepsilon$방정식을 사용하여서 난류 와점성을 구할 수 있다. 자유수면과 동수압을 고려하기 위하여 3단계로 나누어서 해석하였다. 제 1단계에서는 운동량방정식을 연직방향에 대해 음해적으로 차분하였다. 제2단계에서는 유속과 동수압 보정항으로 이루어진 식을 연속방정식에 대입하여 타원형 방정식인 동수압-포와송 방정식을 해석하여 얻어지는 유속은 질량보존법칙을 만족하게 된다. 마지막으로 자유수면과 최종유속을 보정 및 계산하였다. 본 연구에서 제시한 수치모형을 검증하기 위해서, 트렌치 수로에서 난류의 흐름에 변화를 고려하기 위해 수치모의를 하였다. 전반적으로 수치모의에 의한 결과와 실험 자료가 일치하는 경향을 보였다.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.11
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• pp.1168-1179
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• 2006

The validity of an unsteady two-dimensional(2-D) numerical hydrodynamic and pollutant dispersion model(2DNHPDM) was evaluated using the data obtained from I-sa streams in Sooncheon, Chonnam, during rain-fall run-off. Field observations was conducted for 35 hours during the 10 hours rainfall event on 7th May 2005. The water level, 2-D velocity, flow field, and COD at seven points selected along the river were measured at intervals of one hour. The model was applied to describe two-dimensional movement of dissolved pollutants in meandering non-uniform river. Major physical processes affecting the lateral and horizontal mixing of the river flow were simulated. The model was proved effective in describing the hydrodynamics and dispersion of the river pollutants from its major tributaries as well as non-point sources.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.343-346
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• 2005

Three dimensional structures of detonation wave propagating through a square-shaped duct were investigated using computational method and parallel processing. Inviscid fluid dynamics equations coupled with $variable-{\gamma}$ formulation and simplified one-step Arrhenius chemical reaction model were analysed by MUSCL-type TVD scheme and four stage Runge-Kutta time integration. The unsteady computational results in three dimension show the detailed mechanism of transverse mode and diagonal mode of detonation wave instabilities resulting same cell length but different cell width in smoked-foil record.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1088-1092
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• 2006

낙동강은 대표적인 수지상 하천망의 형태로서 댐 방류량, 낙동강 하구언의 수위조절, 지류 유입량, 비점원 유입량 등 계산영역 경계에서의 비정상상태의 수리조건과 수질관리 계획에 의해 일률적으로 오염이 부하되는 정상상태의 수질조건이 공존하고 있는 실정이다. 따라서 본 연구에서는 부정류 수질해석의 선행연구로 갈수기 및 저수기에서 안정한 해를 제공할 수 있는 부정류 수리모형을 개발하였으며, 낙동강에서 실측된 유량자료를 활용하여 개발된 모형의 적용성를 검증하였다. 또한 기존 범용 부등류 수질모형의 수리해석 결과와 비교하여 부정류 수리해석의 필요성을 확인하였다. 낙동강 물환경연구소에서 2004년, 2005년 환경기초조사사업의 일환으로 실측한 유량자료에 의한 본 모형의 모의결과, 동적 저유량의 낙동강 본류 유량 변동 특성을 정확히 모의하고 있는 것으로 판단되었으나 기존 정적 수질 모형에 의한 해석결과는 실측유량, 유속과 수리수심 등에 있어서 동적 해석 결과와 차이를 보이고 있으며, 이는 오염물의 종방향이송과 종확산계수 및 재포기계수 산정에 큰 영향을 미치는 유속, 수리수심 등의 수리량이 실제값과 상이하게 계산되어 수질해석의 불확실성을 가중시키는 결과를 도출하게 될 것으로 판단된다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.8
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• pp.37-45
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• 2002

A two-dimensional unsteady, inviscid flow solver has been developed for the simulation of airfoil-vortex interactions on unstructured dynamically adapted meshes. The Euler solver is based on a second-order accurate implicit time integration using a point Gauss-Seidel relaxation scheme and a dual time-step subiteration. A vertex-centered, finite-volume discretization is used in conjunction with the Roe's flux-difference splitting. An unsteady solution-adaptive dynamic mesh scheme is used by adding and deleting mesh points to take account of both spatial and temporal variations of the flow field. The effect of vortex interaction on the aeroelastic displacement of an airfoil attached to the idealized two degree-of-freedom spring system is investigated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.10
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• pp.939-946
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• 2008

Euler codes or Navier-Stokes codes for compressible flows suffer severe degradation in convergence as Mach number approaches zero. The convergence problem arose from the wide disparity in characteristic speeds can be solved using preconditioning methods without large modifications. In this paper, a preconditioned RANS(Reynolds Averaged Navier-Stokes) solver is developed for analysis of low Mach number flows. In order to validate the method, computational examples are chosen and the results are compared with the experimental data and the existing computed results showing a good accuracy and convergence characteristics for steady inviscid, laminar and turbulent flows at low Mach number.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.3
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• pp.211-219
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• 2008

A three-dimensional inviscid flow solver has been developed based on unstructured meshes for the investigation of the effect of the external stores on the tail surfaces of a generic fighter aircraft. The numerical method is based on a vertex-centered finite-volume discretization and an implicit point Gauss-Seidel time integration. The calculations were made for a steady flow and the computed results were compared with experimental data to validate the flow solver. An unsteady time-accurate computation of the generic fighter aircraft with external stores at transonic flight conditions showed that the external stores cause unsteady loading on the horizontal tail surface due to the mutual interference between their wake and the horizontal tail surface. It was shown that downward deflection of the trailing edge flap significantly reduces the undesirable interference effect.