• Proceeding of EDISON Challenge
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• 2016.11a
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• pp.78-80
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• 2016

우주발사체와 항공 분야에서 초음속과 극초음속 영역에서 비행체의 항력을 최소화하기 위한 최적 형상설계 연구가 활발히 진행되고 있다. 본 논문에서는 마하수 2의 초음속 영역에서 대표적인 비행체 선두부 형상 3가지에 대한 수치해석을 eMEGA 프로그램을 활용해 격자를 생성하고 eDAVA 프로그램을 활용해 유동 해석을 수행하였다. 그 결과 자유유동 마하수 2의 초음속 영역에서는 선두부 형상이 뾰족한 Cone 형상이 3가지 형상 중 작용하는 항력이 가장 적게 나타났고, 선두부가 무딘 형상이 극초음속 영역에서 가장 적합한 현상과 다르게 나타났다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.4
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• pp.245-255
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• 2019

This paper describes on aerodynamic analysis based on the truncation rate of guided-weapon nose using computational fluid dynamics. The shape to perform the analysis is only the body of the guided weapon and the diameter to length ratio is 10.7. Three nose shapes were selected and hemisphere, 25% and 50% truncation were compared. For the accurate CFD analysis of the body, the grid method and the analytical method were selected and verified using NASA wind tunnel test data. For the three nose shapes, the drag analysis for the flight Mach number is 6~20% different. This difference was analyzed by the pressure distribution from nose to base.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.6
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• pp.14-20
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• 2002

The aerodynamic heating at a nose cone is predicted under the KSR-III flight conditions. An equilibrium reacting gas condition is applied. The parametric study is performed with Mach number of 4.9, 10.2 and 15 and for the following nose shapes of hemisphere, cut cylinder and parabola. AUSMPW+ and shock aligned grid technique are used to provide the best aerodynamic solutions. In addition, the composite material of a nose cone is discussed in the viewpoint of a thermal safety.

• Journal of the Korean Society for Railway
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• v.16 no.6
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• pp.454-459
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• 2013

Pressure waves are generated and propagate in a tunnel when train enters tunnel high speed. A compression wave due to the entry of train head propagates along the tunnel and is reflected at tunnel exit as an expansion wave. An expansion wave due to the entry of the train tail propagates along the tunnel and is reflected at tunnel exit as a compression wave. These pressure waves are repeatedly propagated and reflected at the tunnel entrance and exit. Severe pressure changes causes ear-discomfort for passengers in the cabin and micro pressure waves around the tunnel exit. It is necessary to analyze the transient pressure phenomena in tunnels qualitatively and quantitatively, because pressure change rate is considered as one of the major design parameters for optimal tunnel cross sectional area and repeated fatigue force on car body. In this study, we developed a characteristics method based on a fixed mesh system and boundary conditions for crossing trains and analyzed this system using an X-t diagram. The results of the simulation show that offsetting of pressure waves occurs for special entry conditions of a crossing train.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1988.10a
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• pp.271-273
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• 1988

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.71-76
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• 2008

In this study, side force, drag, and the yawing moment were measured based on the angle of attack by using two models of different nose shapes with slender bodies, which were general shapes in the subsonic area. As a result, the side force and yawing moment were the highest at a specific angle of attack. The boundary between asymmetrical normal state and asymmetrical abnormal state were able to be seen. As a result of analyzing the side force, drag, and yawing moment by time, reliability varied depending on the shape of the head at the same angle of attack. The results of measuring pressure distribution from the surface of the slender body at each angle of attack were as follows: as the angle of attack gets higher, the distribution of surface pressure was asymmetrical.

• Journal of the Korean Society for Railway
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• v.15 no.5
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• pp.436-441
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• 2012

Pressure waves are generated and propagate in tunnel when train enters a tunnel with high speed. Compression wave due to the entry of train head propagates along the tunnel and is reflected at tunnel exit as expansion wave. While expansion wave due to the entry of train tail propagates along the tunnel and is reflected at tunnel exit as compression wave. These pressure waves are repeatedly propagated and reflected at tunnel entrance and exit. Severe pressure change per second causes ear-discomfort for passengers in cabin and micro pressure wave around tunnel exit. It is necessary to analyze the transient pressure phenomena in tunnel qualitatively and quantitatively, because pressure change rate is considered as one of major design parameters for an optimal tunnel cross sectional area and the repeated fatigue force on car body. In this study, we developed the characteristics method analysis based on fixed mesh system and compared with the results of real train test. The results of simulation agreed with that of experiment.

• Journal of the Korean Society for Railway
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• v.18 no.4
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• pp.309-316
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• 2015

The contribution of exterior devices such as bogie fairings and pantographs to running resistance was estimated on the basis of coasting tests at up to 350 km/h with the help of the Korean Next Generation High speed train (HEMU-430X). In order to assess the reduction of air resistance by nose car's bogie fairing, coasting tests were conducted with a removable bogie fairing at various speed ranges. And, the contribution of the pantograph to air resistance was also estimated with coasting tests that include the pantograph's rising and descent modes. The linear regression method was used to examine decelerations from time-velocity data and the equation of resistance to motion is proposed from the deceleration data. From the aerodynamic term of the equation of resistance to motion, the contribution to air resistance by nose car's bogie fairing and pantograph was estimated. The results show that the air resistance was reduced by about 3.8% by the nose car's bogie fairing. And, the 3.9% increase of air resistance by the pantograph (open knee mode) has been found.

• 한국전산유체공학회:학술대회논문집
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• 1995.10a
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• pp.49-54
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• 1995

A numerical analysis on the effect of the front shape on the aerodynamic characteristics of HST model is made, using FVM based general purpose 3D Navier-Stokes eq. solver, TURBO-3D program. Numerical solutions are compared with each case of different front shape for HST model. The result shows a good quantitative aerodynamic characteristic tendencies for variation of front shape of HST. Thus it may be used as a basis in the design of the shape of real HST.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.197-201
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• 2004

A design optimization of Sphere-Cone blunt nose hypersonic flight vehicle has been studied by using upwind Navier-Stokes method and numerical optimization method. Heat transfer coefficient and drag coefficient are selected as objective function or design constraint. Control points of Bezier curve are considered as design variable.