• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.19-22
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• 2003

Ejector-diffuser system is one of fluid machinery which can entrain the fluid in low pressure part and transport it to the higher pressure part. The conventional ejector-diffuser system has been pointed out that its overall efficiency is quite low compared with other fluid machinery since it is derived by only the pure shear stresses. In the present study, 4, 6, and 8 lobed petal nozzles with a design Mach number of 1.7 are adopted as a primary nozzle to improve the performance, and are compared with a conventional circular nozzle.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.5
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• pp.21-28
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• 2009

This experimental study was performed to find the important design parameters and the starting characteristics of a supersonic exhaust diffuser. The experimental study was carried out on a scaled down model of straight cylindrical supersonic exhaust diffuser, in order to evaluate the effects of operating fluid(air, nitrogen), the diffuser inlet area over the primary nozzle throat area($A_d/A_t$), the inlet pressure of primary nozzle, diffuser length over diffuser inner diameter($L_d/D_d$) and existence or nonexistence of diffuser divergence. The test results showed that the starting pressure increased with decrease in diameter of primary nozzle, and the measured starting pressure of the diffuser had approximately 90~98% efficiency as compared with the predicted starting pressure. Also, the diffuser was started at all case, regardless of $L_d/D_d$ (above 8.4) and diffuser divergence. The result of this study can be used as an essential database for developing a simulated high-altitude facility for real-scale model.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.8
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• pp.645-651
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• 2015

The objective of this study is to experimentally investigate the effect of design parameter on the mass ratio of a central-driven ejector. The design parameters are the primary nozzle area and distance ratios, diffuser exit-area ratio and mixing-tube length ratio. The experimental setup was an open-loop continuous circulation system which has a movable nozzle ejector, an electric motor-pump, a water tank, a control panel and high-speed camera unit. We calculated the mass ratio using the measured primary and suction-flow rates with the experimental parameter of primary water-flow rate or pressure. The results showed that the mass ratio increased with the primary nozzle distance ratio and mixing tube length ratio, while the mass ratio decreased with the primary nozzle-area ratio and diffuser exit-area ratio.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.5
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• pp.2610-2616
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• 2014

An ejector is a kind of pump which is using pressure energy of high pressure fluid. This study aims to investigate performance influencing according to change the ejector mixing section shape using CFD simulation by Finite Volume Method. Optimum conditions were suggested 3 kind of variable such as nozzle diameter, nozzle length, distance from nozzle tip to the diffuser inlet. The results, It was confirmed that the diameter of the nozzle was the greatest effect in performance of the ejector. The diameter of the nozzle get smaller, mixing ratio was increased. On the other hand, nozzle length, distance from nozzle tip to the diffuser inlet had little effect on performance. It was proposed specific Mixing section, Nozzel diameter 23.8mm using the Artificial Neural Network.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.5
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• pp.411-417
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• 2007

This study has been conducted to investigate pumping characteristics of diffuser/nozzle based piezoelectric micropumps. The micropumps include a piezo disk (an actuator), a chamber and a set of diffuser and nozzle. Flow in the current micropumps is controlled by a set of diffuser and nozzle, not by a nap valve. The diffuser/nozzle based micropumps are more reliable in operation and are easier in manufacturing than the flap valve based micropumps. The flow rates of the piezoelectric micropumps have been closely analyzed with a numerical calculation. It has been found that the positions of the inlet and outlet of the micropump can influence the performance of the diffuser/nozzle based piezoelectric micropumps. This study may provide fundamental understanding for the design and analysis of the piezoelectric micropumps.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.570-573
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• 2012

Performance characteristics of subscale diffuser for high-altitude simulation have been numerically investigated. The length of diffuser entrance with respect to nozzle exit diameter was changed to 0, 50, 100%, respectively. In addition, flow characteristics have been studied for various length to diameter ratio of secondary throat diffuser. As a result, the shape of plume was contracted for insufficient length of diffuser entrance. Also, if the length to diameter ratio of secondary throat diffuser were less than 7 or 8, mach disk has been formed inside the diffuser.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.9
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• pp.563-570
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• 2017

Experimental and numerical studies were performed to investigate the performance and internal flow characteristics of a supersonic second throat exhaust diffuser (STED) with back pressure ($P_a$). An ejector system was used to vary the back pressure ($P_a$) conditions. The operating gas for the STED and the ejector was high pressure nitrogen at room temperature. When the back pressure ($P_a$) at a constant nozzle inlet pressure $P_0$) decreases, the pressure recovery location moves downstream. If the pressure ratio $P_0/P_a$) is the same, even if the nozzle inlet pressures $P_0$) are different, the diffuser's internal flow pattern and starting pressure ratio ($(P_0/P_a)_{st}$) are almost the same.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.04a
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• pp.17-17
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• 2000

이젝터-디퓨저 시스템은 고압의 기체를 노즐로 팽창시켜서 얻은 대량의 운동에너지를 이용하여 낮은 에너지를 가지는 주변의 기체를 외부로 배출시키는데 이용되는 유체 역학적 펌프이다. 이젝터-디퓨저 시스템은 작동부가 없고 구조가 단순하여 설치/보수 및 시스템 전체의 경량화에 많은 이점이 있으므로 그 활용도가 증대하고 있는 추세이다. 그러나 이젝터-디퓨저를 지나는 초음속 유동은 복잡한 충격파 및 난류현상들로 인하여 그 물리적 특성들이 명확히 알려지지 않았다. 특히 이러한 제현상들의 간섭과 전단층의 불안정성 때문에 발생하는 비정상성은 1차 유동과 2차 유동의 혼합작용에 영향을 미쳐, 결국 시스템 전체의 배기성능을 저하시킬 뿐만 아니라, 소음과 진동을 발생시켜 시스템의 안정적인 운전을 방해한다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.10a
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• pp.36-36
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• 1999

일반적으로 이젝터(ejector)는 노즐로부터 팽창하는 높은 운동량을 가지는 주 유동과 주변의 낮은 운동량을 가지는 유동사이에서 생기는 강한 전단력을 이용하여, 분류 주변의 유체를 보다 고압의 부분까지 압축하여 수송하는 장치이다. 이젝터는 노즐(nozzle)과 디퓨저(diffuser)로 되어 있으며, 회전부분이나 활동부분을 가지지 않는 유체기계이므로 고장이 적고, 소형임에도 불구하고 대용량의 유체를 압축할 수 있는 특징을 가지고 있다. 그러나 이젝터의 구동은 유체의 전단력만을 이용하므로 효율이 낮은 단점이 있으므로, 이젝터 형상의 최적설계 및 성능개선을 위한 연구가 필요하다.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.4
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• pp.63-72
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• 2013

A Mach 5 nozzle and a diffuser of the Scramjet Engine Test Facility (SETF) were made for a hydrocarbon-fueled scramjet engine. SETF, attached with a diffuser guide, started with a model of 60% blockage, though the model engine could not start by over expansion of the facility nozzle. The model was moved into the nozzle to escape the shock generated from the nozzle exit, both SETF and the engine could start. The pitot rake experiments (blockage of 2.3%) were done for measuring the core flow in the test section. From the pitot experiments, the core flow was expanded by an under expansion. It means that the core flow in the test section was related with a model blockage. SETF and the engine with a blockage of 33% work normally. From a series of experiments, SETF started with a normal shock efficiency of 58%, regardless of a blockage ratio.