• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.7
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• pp.2347-2355
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• 1996

Purpose of the present study is to develop a computational design program for shape optimization, combining the numerical optimization technique with the flow analysis code. The present methodology is then validated in three cases of aerodynamic shape optimization. In the numerical optimization, a feasible direction optimization algorithm and shape functions are considered. In the flow analysis, the Navier-Stokes equations are discretized by a cell-centered finite volume method, and Roe's flux difference splitting TVD scheme and ADI method are used. The developed design code is applied to a transonic channel flow over a bump, and an external flow over a NACA0012 airfoil to minimize the wave drag induced by shock waves. Also a separated subsonic flow over a NACA0024 airfoil is considered to determine a maximum allowable thickness of the airfoil without separation.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.1
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• pp.50-55
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• 2004

In this study, slit-tones by plane impinging jet are investigated experimentally over the whole subsonic flow range, especially at low speeds, in order to obtain the instability behaviour of impinging plane jet. Slit-tones are generated at low speeds associated with laminar shear layer instability as well as at high speeds associated with turbulent instability. Most of low-speed slit-tones are induced by symmetric mode instability unless the slit is not so wide, in which case antisymmetric modes are induced like edge-tones. It is found that the frequencies at low speeds ate controled by the unstable condition of the vortex at the nozzle exit and its pairings by which the frequencies are decreased by half. In the case of symmetric modes related with low-speed slit-tones, frequencies lower than those associated with one-step pairings are not found.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.17-22
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• 2004

A space launch vehicle departs the ground in a low speed, soon reaches a transonic and a supersonic speed, and then flies in a hypersonic speed into the space. Therefore, the design of a launch vehicle should include the prediction of aerodynamic characteristics for all speed regimes, ranging from subsonic to hypersonic speed. Generally, Empirical and analytical methods and wind tunnel tests are used for the prediction of aerodynamic characteristics. This research presents considerable factors for aerodynamic analysis of a launch vehicle using CFD. This investigation was conducted to determine effects of wake over the base section on the aerodynamic characteristics of a launch vehicle and also performed to determine effects of the sting which exist to support wind tunnel test model.

• 한국전산유체공학회:학술대회논문집
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• 2001.10a
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• pp.138-143
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• 2001

An experimental model to enhance the mixing of parallel supersonic-subsonic jet ($M_1$=1.78 and $M_2$=0.30) is simulated with a numerical technique by modeling the wall-mounted cavity to a boundary condition of oscillating pressure. The computed pilot pressure distributions along three representative cross sections show a good agreement with the equivalent experimental data. The irradiation of acoustic wave in the ultrasonic range causes the mixing augmentation of jet and wake due to the transfer of vibration energy between fluid particles.

• Journal of Mechanical Science and Technology
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• v.18 no.4
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• pp.560-572
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• 2004

Aeroelastic response and control of airfoil-flap system exposed to sonic-boom, blast and gust loads in an incompressible subsonic flowfield are addressed. Analytical analysis and pertinent numerical simulations of the aeroelastic response of 3-DOF airfoil featuring plunging-pitching-flapping coupled motion subjected to gust and explosive pressures in terms of important characteristic parameters specifying configuration envelope are presented. The comparisons of uncontrolled aeroelastic response with controlled one of the wing obtained by feedback control methodology are supplied, which is implemented through the flap torque to suppress the flutter instability and enhance the subcritical aeroelastic response to time-dependent excitations.

• 한국연소학회:학술대회논문집
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• 2002.06a
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• pp.147-153
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• 2002

Experimental investigations are performed on the stability and the structure of bluff-body stabilized hydrogen flames. The velocities of coflow air are varied from subsonic to supersonic velocity of Mach 1.8 and OH PLIF images and Schilieren images are used for analysis. Three characteristic flame modes are classified into three regimes with the variation of fuel-air velocity ratio; a jet like flame, a central-jet dominated flame and a recirculation zone flame. Stability curves are drawn to find the blowout regimes and to show that flame stability is improved by increasing the lip thickness of fuel nozzle that works as bluff-body. $Damk{\ddot{o}hler$ number is adopted in order to scale the blowout curves of each flame obtained at different sizes of the bluff-body and all blowout curves are scaled successfully regardless of its bluff-body size.

• Journal of the Korean Society of Combustion
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• v.12 no.2
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• pp.1-9
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• 2007

This paper describes numerical efforts to investigate combustion characteristics of HyShot scramjet combustor, where gaseous hydrogen is transversely injected into a supersonic cross flow. The corresponding altitude, angle of attack, and equivalence ratio are 35-23 km, $0^{\circ}$, and 0.426 respectively. Two-dimensional simulation reasonably predicts combustor inner pressure distribution and reveals periodic combustion characteristics of HyShot scramjet combustor. Altitude effects are also investigated and the strength of flow instability and subsonic boundary layer thickness affect the combustion efficiency according to altitudes. Frequency analyses provide the flow instability effects on the turbulent combustion in HyShot scramjet combustor.

• Journal of Astronomy and Space Sciences
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• v.16 no.2
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• pp.139-148
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• 1999

Bow shock formation, in case the supersonic solar wind flow is hindered by the atmosphere of Mars, is investigated. The atoms newly ionized from the extensive neutral atmosphere of Mars are loaded to the solar wind. By the conservation of momentum, the solar wind velocity is decreased. Then the supersonic flow velocity drops to the subsonic flow velocity in front of Mars at certain region, which is called the bow shock. The location of Mars subsolar bow shock is highly varying in the range of 1.3 to 2.5 Rm. Martian bow shock location is estimated by one-dimensional flux tube equations reduced from full three-dimensional MHD equations. The variability of Mars bow shock location effected by the solar wind conditions is studied. It is evident that the solar wind dynamic pressure change is able to make the Mars bow shock location variable.

• 한국연소학회:학술대회논문집
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• 2007.05a
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• pp.79-85
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• 2007

This paper describes numerical efforts to investigate combustion characteristics of HyShot scramjet combustor, where gaseous hydrogen is transversely injected into a supersonic cross flow. The corresponding altitude, angle of attack, and equivalence ratio are 35-23 km, $0^{\circ}$, and 0.426 respectively. Two-dimensional simulation reasonably predicts combustor inner pressure distribution and reveals periodic combustion characteristics of HyShot scramjet combustor. Altitude effects are also investigated and the strength of flow instability and subsonic boundary layer thickness affect the combustion efficiency according to altitudes. Frequency analyses provide the flow instability effects on the turbulent combustion in HyShot scramjet combustor.

• Journal of Astronomy and Space Sciences
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• v.23 no.3
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• pp.209-216
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• 2006

Ion acoustic solitary wave in a plasma consisting of electrons and ions with an external magnetic field is reinvestigated using the Sagdeev's potential method. Although the Sagdeev potential has a singularity for n < 1, where n is the ion number density, we obtain new solitary wave solutions by expanding the Sagdeev potential up to ${\delta}n^4$ near n = 1. They are compressiv (rarefactive) waves and shock type solitary waves. These waves can exist all together as a superposed wave which may be used to explain what would be observed in the solar wind plasma. We compared our theoretical results with the data of the Freja satellite in the study of Wu et al. (1996). Also it is shown that these solitary waves propagate with a subsonic speed.