• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.11
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• pp.849-859
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• 2020

The semi-empirical equation and commercial computational tool were used to predict the base drag of a guided missile with free-stream Mach numbers and chamber pressures, and the results were generally agree each other. Differences in flow characteristics and base drags were observed with over/under expansion conditions by the nozzle. Under the over-expansion condition, the base pressure decreased as the expansion fan was generated at upper region of the base, and base pressure decreased further with increasing free-stream Mach number as the expansion becomes strong. Under the under-expansion conditions, a shock wave was generated around the base by the influence of the nozzle flow, which increased the base pressure, and the effect increased as the chamber pressure increased. Under the same chamber pressure condition, as the free-stream Mach number increases, the characteristic that the base pressure decreases as the shock wave generated at the base moves downstream was observed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.10
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• pp.955-966
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• 2009

DES method is applied to an axisymmetric base flow at supersonic mainstream. The model is based on the Spalart-Allmaras (S-A) turbulence model in the RANS mode, and is based on the subgrid scale model in the Large-eddy simulation (LES) mode. Accurate predictions of the base flowfield and base pressure are successfully achieved by using the DES methodology which is less expensive than LES. Flow properties at the edge of base, such as boundary layer thickness, momentum thickness and skin fraction are compared with Dutton et al [experimental data to proper prediction of base flowfiled. From the present results, The DES accurately resolves the physics of unsteady turbulent motions, such as shear layer rollup, large-eddy motions in the downstream region and small eddy motions inside the recirculating region. Moreover, The present results of using an empirical constant $C_{DES}$ of 1.2 shows good agreement with experimental data than conventional empirical constant $C_{DES}$ of 0.65.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.9
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• pp.27-33
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• 2005

This research presents the influence of the base region modeling on the aerodynamic characteristics of a launch vehicle using CFD. The vicinity of a launch vehicle is divided into four zones, and four computational cases are made using these four zones. The aerodynamic coefficients are predicted for the angle-of-attack of 6 degrees and Mach numbers ranging from 0.4 to 2.86. It was found that modeling of the base region should not be neglected for the prediction of the aerodynamic characteristics of a launch vehicle in subsonic and transonic regions. It was also found that the modeling of the sting support used in the wind tunnel test is necessary to get a better agreement with the experiments.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.327-330
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• 2006

Numerical simulations were carried out to investigate the base drag characteristics of a base bleed projectile with a central propulsive jet by considering the base homing process. Overall fluid dynamic process is modeled by Wavier-Stokes equations for reacting flows with two-equation $k-\omega$ SST turbulence closure. The combustion process is modeled by finite-rate chemistry with a given partially burned exit condition of the BBU (base-bleed unit). Besides the demonstrating the capability of the present CFD solver for the base drag and the interaction of the base flow with a rocket plume, present study gives an insight into the fluid dynamics and the combustion process of the hybrid-propulsion projectile.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.3
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• pp.372-377
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• 2010

The objective of this study is to predict the drag of an axisymmetric underwater vehicle with bluff afterbody using CFD. FLUENT, commercial CFD code, is used to simulate high Reynolds number turbulent flows around the vehicle. The computed drag coefficients are compared to available experimental data at various Reynolds numbers. Four widely used two-equation turbulence models are investigated to evaluate their performance of predicting the anisotropic turbulence in a recirculating flow region, which is caused by flow separation arising from the base of the vehicle. The simulations with Realizable ${\kappa}-{\varepsilon}$ and ${\kappa}-{\omega}$ SST turbulence models predict the anisotropic turbulent flows comparatively well and the drag prediction results with those models show good agreements with the experimental data.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.83-86
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• 2007

Turbulent flow analysis is conducted around the multi-stage launch vehicle including base region and detachment motion of strap-on boosters due to resultant aerodynamic forces and gravity is simulated. Aerodynamic solution procedure is coupled with rigid body dynamics for the prediction of separation behavior. An overset mesh technique is adopted to achieve maximum efficiency in simulating relative motion of bodies and various turbulence models are implemented on the flow solver to predict the aerodynamic forces accurately. At first, some preliminary studies are conducted to show the importance of base flow for the exact prediction of detachment motion and to find the most suitable turbulence model for the simulation of launch vehicle configurations. And then, developed solver is applied to the simulation of KSR-III, a three-stage sounding rocket researched in Korea. From the analyses, after-body flow field strongly affects the separation motions of strap-on boosters. Negative pitching moment at initial stage is gradually recovered and a strap-on finally results in a safe separation, while fore-body analysis shows collision phenomena between core rocket and booster. And a slight variation of motion is observed from the comparison between inviscid and turbulent analyses. Change of separation trajectory based on viscous effects is just a few percent and therefore, inviscid analysis is sufficient for the simulation of separation motion if the study is focused only on the movement of strap-ons.

• Proceedings of the KGS Conference
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• 2004.05a
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• pp.54-54
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• 2004

본 연구에서는 광주광역시 지하수의 수질 및 이용형태를 분석하고, 수질의 지화학적 조성을 통해 지하수의 유동기구를 추정하고자 한다. 그 결과를 기초로 지하수의 오염방지 및 지하수 이용에 대한 제반 관리방안을 제시하는데 연구의 목적이 있다. 화강암질 편마암은 광주지역의 기저가 되는 암석으로서 동남부의 일부지역에 부분적으로 분포하고 있으며, 북동부와 남서부의 축을 중심으로 넓게 분포한 화강암은 대부분 쥬라기때 관입한 조립질 흑운모화강암으로서 풍화에 약하여 300m이하의 낮은 능선을 이루고 있다. (중략)

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.1072-1076
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• 2017

In this paper, a numerical study has been performed to analyze flow characteristics of rocket propulsion. Through the ground spin test, combustion chamber pressure was measured. Based on the experimental results, numerical analysis was conducted under various nozzle pressure ratio conditions such as standard, operating and base pressure conditions. And it was compared with quasi-1D solution and experimental result. In addition, the difference in thrust characteristics according to the spin/non-spin of the flow conditions was confirmed at the same nozzle pressure ratio.

• Journal of the Korean Geographical Society
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• v.34 no.1
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• pp.1-16
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• 1999

본 연구는 도시화에 수반되는 지하수의 수문황경 변화를 조사하기 위해, 일본 하다노 분지를 대상으로 수문지질을 밝히고, 인위적인 요인에 의한 수문환경 변화와 수문특성을 종합적으로 분석하였다. 그 결과, 분지의 대수층은 퇴적환경에 의해 TP층을 경계로 신기 loam층과 고기 loam층으로 나눌 수 있으며, 전자를 천층지하수의 대수층, 후자를 심층지하수의 대수층으로 구분할 수 있다. 그리고 대수층의 기저기복은 지하수 수위의 공간적 차이를 유발하고, 지하수 유동계에 큰 영향을 미치고 있다. 분지의 심층지하수의 주요 공급원은 탄자와 산지의 지표수이고, 천층지하수는 분지 내에 내리는 빗물에 기인한 것으로 간주된다. 지하수의 과잉양수는 지하수 수지의 불균형을 유발함으로서 심층지하수가 매년 0.12~0.14m씩 저하되고 있다. 대체로 Cl-, NO3-농도는 심층지하수보다 천층지하수에서 높으며, 선정부에서 선단부로 갈수록 높아지는 것으로 보아 분지의 지하수 수질형성에 인위적인 요인이 크게 작용하고 있는 것으로 사료된다. 지하수의 화학적 조성은 대체로 Ca(HCO3-)2형에 속한다.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.1
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• pp.35-45
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• 2005

Numerical study is carried out to investigate the effects of chemistry and thermal radiation on the rocket plume flow field at various altitudes. Navier-Stokes equations for compressible flows were solved by a fully-implicit TVD code based on the finite volume method. An infinitely fast chemistry module for hydrocarbon mixture with detailed thermo-chemical properties and a thermal radiation module for optically thick media were incorporated with the fluid dynamics code. The plume flow fields of a kerosene-fueled rocket flying at Mach number zero at sea-level, 1.16 at altitude of 5.06 km and 2.90 at 17.34 km were numerically analyzed. Results showed the plume structures at different altitude conditions with the effects of chemistry and radiation. It is understood that the excess temperature by the chemical reactions in the exhaust gas may not be ignored in the view point of propulsion performance and thermal protection of the rocket base, especially at higher altitude conditions.