• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
• /
• pp.753-762
• /
• 2004

Conceptual studies of a combined-cycle engine have been conducted. Herein, the results are presented. The engine is composed of ejector-jet, ramjet, scramjet and rocket modes, and will be mounted on the Single-Stage-to-Orbit aerospace plane. Propellants are hydrogen and oxygen. Calculated engine thrust performances and cooling requirement of the engine are presented. Pitching moment of the plane with the engine will be balanced even in the vacuum condition. The experimental results of the inlet and the ejector-jet, ramjet and scramjet modes are presented. The effect of the airframe configuration on the engine performance and the thermal environment in the in-side of the plane are also presented. Through the investigations, possibilities of the combined-cycle engine and the aerospace plane are being made clear now.

• 대한기계학회논문집B
• /
• 제28권8호
• /
• pp.887-894
• /
• 2004

A technique of mixing enhancement by using an elliptic jet screech reflector has been examined experimentally in an underexpanded sonic round jet where jet screech tone is generated. Since jet screech is known to enhance jet spreading, a reflector was designed to focus jet screech waves near the nozzle lip at an underexpanded jet. The reflector has an elliptic cross section of which one focus is located near the nozzle lip and the other in the jet screech source region in a plane including the jet axis. In the jet with the elliptic reflector, the mass flow rate showed a significant increase in the jet entrainment when compared to that for the small disk reflector. This was attributed to the increased screech amplitude near the nozzle lip as well as the mode change of the jet. The jet mixing was also increased by the amplified jet screech at two other underexpanded jets, but the jet oscillation mode did not change.

• Journal of Mechanical Science and Technology
• /
• 제14권12호
• /
• pp.1386-1395
• /
• 2000

The mear field structure of round turbulent jets with initially asymmetric velocity distributions is investigated experimentally. Experiments are carried out using a constant temperature hot-wire anemometry system to measure streamwise velocity in the jets. The measurements are undertaken across the jet at various streamwise stations in a range starting from the jet exit plane and up to a downstream location of twelve diameters. The experimental results include the distributions of mean and instantaneous velocities, vorticity field, turbulence intensity, and the Reynolds shear stresses. The asymmetry of the jet exit plane was obtained by using circular cross-section pipes with a bend upstream of the exit. There pipes used here include a straight pipe, and 90 and 160 degree-bend pipes. Therefore, at the upstream of the upstream of the pipe exit, secondary flow through the bend mean streamwise velocity distribution could be controlled by changing the curvature of pipes. The jets into the atmosphere have two levels of initial velocity skewness in addition to an axisymmetric jet from a straight pipe. In case of the curved pipe, a six diameter-long straight pipe section follows the bend upstream of the exit. The Reynolds number based on the exit bulk velocity is 13,400. The results indicate that the near field structure is considerably modified by the skewness of an initial mean velocity distribution. As the skewness increases, the decay rate of mean velocity at the centerline also increases.

• 한국항공우주학회지
• /
• 제33권1호
• /
• pp.48-53
• /
• 2005

본 연구의 목적은 기계적인 전단층 자극방법을 이용 스월제트 혼합향상의 가능성을 고찰함에 있다. 이를 위해 기계적 자극장치가 설계, 제작되었다. 주요 구성품으로는 두개의 아음속 노즐, 스월 발생기, 그리고 유동 자극기 등이다. 실험은 다음과 같은 다양한 헬리컬 모드들에서 수행되었다; m=+0, m=$\pm$1, m=$\pm$2, m=$\pm$3, m=$\pm$4. 열선유속계를 이용한 plane 파동과 헬리컬 파동 자극에 따른 제트속도 측정이 이루어 졌다. 다양한 헬리컬 모드에서의 결과 값들이 기준 값(plane-wave)과 비교되었다. 획득된 결과는 3-D mesh plot 과 2-D contour plot으로 표현되었다. 이로써 새로 고안된 장치는 헬리컬 불안정파 자극에 대한 효과를 입증하였고 또한 결과적으로 스월제트의 혼합을 증진시켰다.

• 한국항공우주학회지
• /
• 제41권6호
• /
• pp.473-480
• /
• 2013

2020년 예정인 국내 달 탐사 프로그램을 위하여 달착륙선에 관한 다양한 연구가 진행되고 있다. 본 연구에서는 RCS jet을 고려한 달 착륙선의 Powered descent phase에서의 유도제어시스템을 구성하고 통합 시뮬레이션을 수행하였다. 달착륙선은 RCS 제트추력기를 이용하여 자세를 제어하므로 일반적인 비례제어기가 아닌 뱅뱅제어기를 사용하게 된다. 본 논문에서는 16개의 추력기를 이용하여 자세제어를 수행하고, 이를 위하여 phase-plane 스위칭 함수를 이용한 on/off 제어기와 추력기 선택 알고리즘을 적용하였다. 또한 Fuzzy logic을 이용한 유도 알고리즘을 이용하여 최적기법을 통해 생성된 기준경로에 따라 정확하고 안전하게 착륙 할 수 있음을 확인 하였다.

• 한국분무공학회지
• /
• 제4권4호
• /
• pp.38-45
• /
• 1999

The near field structure of round turbulent jets with initially asymmetric velocity distribution is investigated experimentally. Experiments were carried out using a constant temperature hot-wire anemometry system to measure streamwise velocity in the jets. The measurements were undertaken across the jet at various streamwise stations in a range starting from the jet exit plane and up to a downstream location of twelve diameters. The experimental results include the distribution of mean and instantaneous velocities, vorticity field, turbulence intensity, and the Reynolds shear stress. The asymmetry of the jet exit plane was obtained by using circular cross-section pipes with a bend at the upstream of the exit. Three pipes were used for this study: A straight pipe, 90 and 160 degree-bended pipes. Therefore, at the upstream of the pipe exit, the secondary flow through the bend and the mean streamwise velocity distribution could be controlled by changing the curvature of pipes.

• Water Engineering Research
• /
• 제3권3호
• /
• pp.163-176
• /
• 2002

In this study, laboratory experiments have been performed to investigate characteristics of the velocity fields and turbulence for non-buoyant plane jet in the vicinity of the jet nozzle using PIV system. The experimental results show that, in the transition region, the lateral velocity profile is in good agreement with Gaussian distribution. However, the coefficient of Gaussian distribution, $\K_{u,}$, decreases with longitudinal distance in the transition region. The existing theoretical equation for the centerline velocity tends to overestimate the measured data in the transition region. A new equation for the centerline velocity derived by incorporating varying $k_{u}$ gives better agreement with the measured data than the previous equation. The results of the turbulence characteristics show peak values are concentrated on the shear layers. The Reynolds shear stress profile shows the positive peak in the upper layer and negative peak in the lower layer. The turbulent kinetic energy also provides double peaks at the shear layers. The peak of the Reynolds shear stress and the turbulent kinetic energy increases until x/B=8, and then it decreases afterwards.s.

• Journal of Mechanical Science and Technology
• /
• 제15권4호
• /
• pp.522-530
• /
• 2001

An experimental study of compressible jet flows has been undertaken in a small transonic wind tunnel. The aim of this investigation was to realize a jet simulator in the framework of wing/nacelle integration research and to characterize the jet flow behavior. First, free jet configuration, and subsequently jet flow in co-flowing air stream configuration were analyzed. Flow conditions were those encountered in a typical flight condition of a generic transport aircraft, i.e. fully expanded sonic jet flows interacting with a compressible external flowfield. Conventional experimental techniques were used to investigate the jet flows-Schlieren visualization and two-component Laser Doppler Velocimetry (LDV). The mean and fluctuating properties were measured along the jet centerline and in the symmetric plane at various downstream locations. The results of two configurations show remarkable differences in the mean and fluctuating components and agree well with the trend observed by other investigators. Moreover, these experiments enrich the database for such flow conditions and verify the feasibility of its application in future aerodynamic research of wing/nacelle interactions.

• 대한기계학회논문집B
• /
• 제29권2호
• /
• pp.214-223
• /
• 2005

The characteristics of flow on two parallel plane jets was experimentally investigated. The two nozzles each with an aspect ratio of 20 were separated by 6 nozzle widths. Reynolds number based on nozzle width was set to 5,000 by nozzle exit velocity. The particle image velocimetry and pressure transducer were employed to measure turbulent velocity components and mean static pressure, respectively. In case of unventilated parallel plane jets, it was shown that a recirculation zone with sub-atmospheric static pressure was bounded by the inner shear layers of the individual jets and the nozzles plated. There was no recirculation zone in the ventilated parallel plane jets. It was found that the spanwise turbulent intensities of unventilated jets were higher than those of ventilated jets because of the interaction of jets, and the streamwise turbulent intensities of ventilated jets were higher than those of unventilated jets because of the effect of entrainment.

• 대한기계학회논문집
• /
• 제12권5호
• /
• pp.1150-1157
• /
• 1988

본 연구에서는 수치계산을 통해 진행하는 방향에 수직으로 일정한 압력구배를 받는 2차원 난류 자유제트의 발달을 고려해 보고자 한다.속도장을 구한 후에는 제 트의 온도가 주위온도 보다 높을 경우와 또 제트를 사이에 둔 양쪽 유체에 온도차가 있을때의 열확산 특성도 함께 알아보려는 것이다. 수직 방향으로 압력구배가 있는 유동장은 최근 활발히 연구가 진행되는 분야인 제트축에 수직방향으로 주위유동이 있 는 경우와 흡사하며 제트를 통한 열확산현상은 air curtain등 실제 응용도가 큼에도 불구하고 문헌에 보고된 것이 별로 없는 것으로 보여진다.