• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.2
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• pp.33-39
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• 2008

To improve the mixing efficiency and to reduce the pressure loss, it is needed to develope a new mixing device for supersonic combustion. The vent mixer is introduced as the new supersonic fuel-air mixer. Computational analyses, that include pressure profile, density contour, and streamline tracing, have been carried out. The expansion wave generates at the end of the extended upper wall of the mixer. And it reduces the shock wave from the hole. Incoming air flow through the hole makes several recirculation regions which increase the mixing efficiency, and the separation region at the downward wall expends the boundary layer which reduces the pressure loss.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.546-549
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• 2009

Dynamic model for supersonic engine is proposed to design control law. The model structure is constructed to capture the local characteristics of supersonic and subsonic flow by using conservation equations. To evaluate the stability of control law under the disturbances, the air turbulence model is incorporated with the engine model. The combined model shows analogous results compared to performance analysis model which is good coincidence with CFD results and disturbance effects.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.12
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• pp.3980-3990
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• 1996

When a moist air is rapidly expanded in a supersonic nozzle, nonequilibrium condensation occurs at a supersaturation state. Condensation shock wave appears in the nozzle flow if the releasing latent heat due to condensation goes beyond a critical value. It has been known that self-excited oscillations of the condensation shock wave generate in an air or a steam nozzle flow with a large humidity. In the present study, the passive control technique using porous wall with a cavity underneath was applied to the condensation shock wave. The effects of the passive control on the steady and self-excited condensation shock waves were experimentally investigated by Schlieren visualization and static pressure measurements. The result shows that the present passive control is a useful technique to suppress the self-excited oscillations of condensation shock wave.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.2
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• pp.697-709
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• 1996

Supersonic axisymmetric jets issuing from various kinds of nozzles with a throat diameter of a few millimeters were experimentally investigated. The exit Mach number and Reynolds number based on the throat diameter of nozzle were in the range of 1.0 ~ 5.9 and 8.4$\times$ $10^4$ ~ 2.9$\times$$10^6$, respectively. The nozzle pressure ratio was varied from 5 to 85. Present paper aims to offer fundamental information of the supersonic free-jets, with an emphasis to give data with which the shape of the free-jets can be depicted under a specified condition. Experimental data are summarized to enable an estimation of the shape of the supersonic free-jets. The result shows that the shape of free-jets is dependent on only the nozzle pressure ratio.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.38.2-38.2
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• 2009

마이크로노즐은 우주공간에서 인공위성의 자세를 바로잡는 데 필요한 마이크로 로켓에 들어가는 필수적인 부품이다. 마이크로 노즐은 또한 나노입자 적층 시스템(nano-particle deposition system, NPDS)에 들어갈 수 있다. NPDS는 세라믹 또는 금속 나노분말 입자를 노즐을 통해 초음속으로 가속시킨 뒤 상온에서 이를 기판에 적층시키는 새로운 시스템이다. 본 연구의 목표는 NPDS에 쓰이는 노즐을 일반적인 반도체 공정을 이용하여 마이크론 스케일의 목을 갖도록 한 마이크로노즐을 제작하는 데 있다. 보쉬 공정은 이러한 마이크로노즐을 제작하는데 필수적인 공정으로, 유도결합플라즈마를 이용해 실리콘 웨이퍼를 식각시키는 기술을 말한다. 보쉬 공정에 사용되는 플라즈마 기체는 $SF_6$와 $C_4F_8$인데, 이 두 가지 기체를 번갈아가면서 사용하여 실리콘 웨이퍼를 이방성 식각하는 것이 그 특징이다. 보쉬 공정에는 다양한 변수가 존재하며 이를 적절히 통제하면 마이크로노즐에 적합한 프로파일을 실리콘 웨이퍼 내에 형성시킬 수 있다. 본 연구에서는 보쉬 공정을 이용하여 3차원 마이크로 노즐을 제작하였다. 기존에 반응성이온식각(deep reactive ion etching, DRIE) 공정을 통해 마이크로노즐을 제작한 사례가 많이 보고되었지만 이들은 모두 2차원적으로 마이크로노즐을 제작하였다. 2차원적으로 제작한 마이크로노즐은 마이크로 로켓에 주로 사용되었지만, 초음속으로 가속된 분말이 노즐의 형상으로 인한 유체 흐름의 불안정성 때문에 NPDS에서는 오래도록 사용할 수 없다는 문제점이 있다. 그러므로 본 연구에서는 마이크로노즐을 3차원 형상으로 제작함으로써 이러한 문제점을 해결하고자 하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.3
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• pp.1083-1095
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• 1996

Shock wave/boundary layer interaction frequently causes the shock wave to oscillate violently and thus the global flow field to unstabilize. In order to stabilize the shock wave system in the diffuser of a supersonic wind tunnel, the present study attempted to control the shock oscillations by using a passive control. A porous wall with the porosity of 19.6% was mounted on a shallow cavity. Experiment was made by means of schlieren optical observation and wall pressure measurements. The flow Mach number just upstream the shock system and Reynolds number based on the turbulent boundary layer thickness were 2.1 and 1.8 * 10$\^$6/, respectively. The results show that the present passive control method on the shock wave/boundary layer interaction in the supersonic diffuser can significantly suppress the oscillations of shock system, especially when the shock system locates at the porous wall.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.6
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• pp.1994-2004
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• 1996

Numerical calculation was applied to supersonic under-expanded jets, and compared with the results of a linear theory and other experiments. TVD difference scheme was employed to solve 2-dimensional and axisymmetric inviscid Euler equation. This paper aims to explore the effects of angle of divergence and design Mach number of nozzle on the structure of under-expanded jets. The angle of divergence was varied from 0 to 20 deg. The results show that the length of the first cell of the under-expanded jets decreases and Mach disk generates at lower nozzle pressure ratio, if the angle of divergence or design Mach number of nozzle increases. The distance from the nozzle exit to Mach disk in 2-dimensional jets becomes much larger than that of axisymmetric jets, and the widths of the jet boundary and the barrel shock wave are also larger than that of axisymmetric jets. Calculation results indicate that the configuration of the under-expanded jets is strongly dependent on the nozzle pressure ratio.

• Journal of the KSME
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• v.35 no.1
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• pp.71-83
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• 1995

최근 충격파현상을 이용하여 고온 고압의 상태를 용이하게 발생시킬 수 있는 기술 및 장치들이 여러 분야에서 요구되고 있으며, 이들에 대한 연구의 필요성이 갈수록 증대되어 가고 있다. 그 러나 우리나라에서의 충격파현상에 대한 이해와 지식은 비압축성 유체공학에 대한 연구에 비해 매우 미비한 실정이며, 이에 대한 관ㅅ미과 체계적인 연구가 절실한 실정이다. 일반적으로 충 격파현상을 이해하는 데에는 압축성 비정상흐름, 혹은 정상적인 초음속흐름에 대한 지식이 필 요하지만, 이 글에서는 충격파현상에 대한 이론적 기술들을 생략하고, 충격파현상들을 소개하기 위한 목적으로 충격파현상에 대한 현재의 연구동향과 충격파현상을 응용하는 실례들에 관해 간략히 기술하고, 충격파현상의 연구를 위해 필요한 충격과 발생장치에 대해서 기술하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1311-1319
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• 1990

For the purpose of preventing the flow undulation in the cascade of steam turbine, the blades are made into a constant expansion rate in static pressure. And the flow in those cascades is transonic or supersonic in the range of 0.7-2.0 in Mach number. As a consequence, an oblique shock wave, known as inner or outer edge shock wave, arises in the flow of cascades. Especially when the steam in cascades is in a state of high wetness, nonequilibrium condensation and condensation shock wave occur, and they give rise to an interference with oblique shock wave. In the present study the case of expansion of moist air through a supersonic nozzle of constant expansion rate, which behaves similar to that of wet steam, was adopted. The effect of nonequilibrium condensation on the oblique shock wave generated by placing the wedge into the supersonic part of the nozzle was investigated. Furthermore, the relationship between nonequilibrium condensation zone and incident point of the oblique shock wave, oblique shock wave angle, the variations of angles of incident and reflected shock waves due to the variation of initial stagnation supersaturation and the relationship between the height of Mach stem and initial stagnation supersaturation are discussed.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.104-111
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• 2009

The existing code which solves two-dimensional RANS(Reynolds Averaged Navier-Stokes) equations and 2-equation turbulence model equations was modified to enable numerical simulation of various supersonic flows. For this, various boundary conditions have been implemented to the code. Bleed boundary condition was incorporated into the code for calculating wall mean flow quantities. Furthermore, the boundary conditions for the turbulence quantities along rough surfaces as well as porous walls were applied to the code. The code was verified and validated by comparing the computational results against the experimental data for the supersonic flows over bleed region on a flat plate. Using the newly modified code, numerical simulations were performed and compared with other computational results as well as the experimental data for the supersonic flows over an oblique shock with a bleed region.