• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.768-773
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• 2004

When a gas expands through a convergent nozzle in which the ratio of the ambient to the stagnation pressures is higher than that of the critical one, the issuing jet from the nozzle is underexpanded. If a flat plate is placed normal to the jet at a certain distance from the nozzle, a detached shock wave is formed at a region between the nozzle exit and the plate. In general, supersonic moist air jet technologies with nonequilibrium condensation are very often applied to industrial manufacturing processes. In spite of the importance in major characteristics of the supersonic moist air jets impinging to a solid body, its qualitative characteristics can not even know. In the present study, the effect of the nonequilibrium condensation on the underexpanded moist air jet impinging on a vertical flat plate is investigated experimentally. Flow visualization and impact pressure measurement are performed for various relative humidities and flat plate positions. The obtained results show the plate shock and Mach disk are dependent on the nozzle pressure ratio and the relative humidity, but for a given nozzle pressure ratio, the diameters of the plate shock and Mach disk depend on the stagnation relative humidity. The impact pressure deviation from the flow of without condensation is large, as the relative stagnation humidity increases.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1194-1197
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• 2005

Micro nozzle is employed as a dynamic passive valve in micro fluidic devices. Micro nozzle array is used in micro droplet generation in bio-medical applications and propulsion device for actuating satellite and aerospace ship in vacuum environments. Aperture angle and the channel length of the micro nozzle affect its retification efficiency, and thus it is needed to produce micro nozzle precisely. MEMS process has a limit on making a micro nozzle with high-aspect ratio. Reactive ion etching process can make high-aspect ratio structure, but it is difficult to make the complex shape. Focused ion beam deposition has advantage in machining of three-dimensional complex structures of sub-micron size. Moreover, it is possible to monitor machining process and to correct defected part at simultaneously. In this study, focused ion beam deposition was applied to micro nozzle production.

• Journal of Advanced Marine Engineering and Technology
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• 제32권4호
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• pp.550-556
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• 2008

The aim of this research is to analyze the influence of motive pressure, driving nozzle position and nozzle throat ratio on the performance of ejector. The experiment was conducted in the variation of motive pressure of 0.196, 0.294, 0.392 and 0.490MPa respectively. The position of driving nozzle was varied in difference locations according to mixing tube diameter(0.5d, 1d, 2d, 3d, 4.15d, 5d and 6d). The experimental results show when the nozzle outlet is located at 3d, the flow characteristics change abruptly. It is shown that the suction flow rate and pressure lift ratio of ejector is influenced by the driving nozzle position. At nozzle position location of the Id of mixing tube diameter the performance of ejector gives the best performance.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.192-197
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• 2004

Recently, fluidic thrust vectoring methods have been preferably employed to control the movement of propulsive systems due to relatively simpler design and lower cost than mechanical thrust vectoring methods. For An application of the thrust vectoring to flight bodies, it is necessary to understand very complicated exhaust flows which are often subject to shock waves and boundary layer separation. But researches for the thrust vector control using counterflow have been few. In the present study, experiments have been performed to investigate the characteristics of supersonic jets controlled by a thrust vectoring method using counterflow. The primary jet is expanded through a two-dimensional primary nozzle shrouded by collars, and is deflected by the suction of the air near nozzle into an upper slot placed between the primary nozzle and the upper collar. A shadowgraph method is used to visualize the supersonic jet flowfields. Primary nozzle pressure ratios and suction nozzle pressure ratios are varied from 3.0 to 5.0, and from 0.2 to 1.0 respectively. The present experimental results showed that, for a given primary nozzle pressure ratio, a decrease in the suction nozzle pressure ratio produced an increased thrust vector angle. As the suction nozzle pressure ratios were increased and decreased, the hysteresis of the thrust vectoring was observed through the wall pressure distributions

• 한국추진공학회지
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• 제5권1호
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• pp.34-41
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• 2001

고온의 연소가스로부터 노즐 표면을 보호하기 위하여 슬롯을 통하여 냉각 유체를 분사하는 슬롯 막냉각에 대하여 연구하였다. 냉각효율 및 열전달 특성은 주유동과 2차 유동의 분사율에 따라 크게 달라지며, 형상변화 및 유동가속에 의해서도 냉각 효과의 변화를 가져오게 된다. 본 연구에서는 실험을 통하여 축소노즐에서 분사율 변화에 따른 슬롯 막냉각 열전달 특성을 고찰하고, 평판 슬롯 막냉각 경험식의 결과와 비교하였으며, 수치해석을 통하여 축소노즐과 원형관에서의 냉각효율 및 열전달 특성도 비교하였다. 상대적으로 낮은 분사율에서 분사율 증가에 따른 냉각효율의 증가가 크게 나타났으며, 일정 분사율 이상에서는 냉각 효율의 증가가 크게 둔화되었다

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.233-236
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• 2002

The high-pressurized spray nozzle is used f3r special washing and cutting with strong impact force. The performance of this nozzle, which focused on spray penetration and radial dispersion, was mainly investigated to maximize the momentum and minimize the flow loss. Hence, our experimental research was conducted by changing the aspect ratio ranging from 0 to 3 with nozzle outlet of 1.1. The spray trajectory far high-pressurized water was experimentally investigated using PDPA diagnostics, which was available at spray downstream region. As the spray at upstream near the nozzle exit did not show the improved disintegration. The results showed empirical correlation with regard to non-dimensional axial velocity distribution, spray penetration, and radial spreading rate with photographic visualization.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2006년도 추계학술대회 논문집
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• pp.145-148
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• 2006

In order to design a micro-thruster which controls the altitude of a space vehicle for a very long lifetime, the flow field should be analyzed considering the nozzle geometry and the difference between stagnation and environmental pressures and so on. This paper describes the axisymmetric non-reacted computational results which were carried out to understand the basic flow phenomena according to the high nozzle pressure ratio. The area ratio is about 56 and the diameter of a nozzle exit is about 0.46 inch. The Mach cell and waves are predicted well.

• 한국가시화정보학회지
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• 제8권2호
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• pp.31-39
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• 2010

Hysteresis is an effect by which the order of previous events influences the order of subsequent events. Hysteresis phenomenon of supersonic internal flows with shock waves has not yet been clarified satisfactorily. In the present study, experiments are carried out on internal flow in a supersonic nozzle to clarify the hysteresis phenomena for the shock waves. Flow visualization is carried out separately on the straight and divergent channels downstream of the nozzle throat section. Results obtained were compared with numerically simulated data. The results confirmed hysteresis phenomenon for shock wave in the Laval nozzle at a certain specific condition. The relationship between hysteresis phenomenon and the range of the rate of change of pressure ratio with time was shown experimentally. The existence of hysteretic behavior in the formation, both the location and strength, of shock wave in the straight part of the supersonic nozzle with a range of pressure ratio has also been confirmed numerically.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2001년도 춘계 학술대회논문집
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• pp.134-143
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• 2001

Viscous solutions of supersonic jet impinging on a flat plate normal to the flow are simulated using three-dimensional Navier-Stokes solver. The jet impinging flow structure exhibits such complex nature as shock shell, plate shock and Mach disk depending on the flow parameters. Among others, the dominant parameters are the ratio of the nozzle exit pressure to the ambient pressure and the distance between the nozzle exit plane and the impinging plane. In the present study, the nozzle contour and the pressure ratio are held fixed, while the jet impinging distance is varied to illuminate the characteristics of the jet plume with the distance. As the plate is placed close to the nozzle at 3D high, the computed wall pressure at or near the jet center oscillates with large amplitude with respect to the mean value. Here D is the nozzle exit diameter. The amplitude of wall pressure fluctuations subsides as the distance increases, but the maximum pressure level at the plate is achieved when the distance is about 4D high. The frequency of the wall pressure is estimated at 6.0 kHz, 9.3 kHz, and 10.0 kHz as the impinging distance varies from 3D, 4D, to 6D, respectively.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1637-1642
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• 2004

Experimental and computational studies were performed to investigate the effectiveness of a thrust vectoring method using a counterflow concept. A shadowgraph method was used to visualize the supersonic jet expanded from a two-dimensional convergent-divergent nozzle and deflected by a now suction. The primary nozzle pressure and suction nozzle pressure ratios are varied between 3.0 and 5.0, and between 0.2 and 1.0 respectively. The present experimental and computational results showed that, for a given primary nozzle pressure ratio, a decrease in the suction nozzle pressure ratio produced an increased thrust vector angle, and during the change processes of the suction pressure, a hysteresis effect of the thrust vectoring was found through the wall pressure distributions.