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스크램제트 엔진용 공기 보조형 인젝터의 분무 가시화 및 미립화 특성에 관한 연구
이진희(Jinhee Lee),이상훈(Sanghoon Lee),이경재(Kyungjae Lee),김재호(Jaiho Kim),양수석(Sooseok Yang) 한국추진공학회 2017 한국추진공학회지 Vol.21 No.5
As a part of the development procedures of scramjet engine with a regenerative cooling system, this experiment was performed using air-assist type injectors for scramjet engine. Two types of injectors were used in this experiment with the 90 and 60 degrees of the injection angle to the main flow. Mie-scattering was used for spray visualization and PDPA was used for the measurement of the atomization characteristics. It was found that increasing the pressure of supplied gas and the distance from nozzle tip led to the enhancement atomization characteristics and the injector with 60 degrees injection angle has better atomization characteristics than 90 degrees injector.
이권희,구병수,김희동,Lee, Gwon-Hui,Gu, Byeong-Su,Kim, Hui-Dong 대한기계학회 2001 大韓機械學會論文集B Vol.25 No.12
Supersonic coaxial jets are investigated numerically by using the axisymmetric, Wavier-Stokes equations which are solved using a fully implicit finite volume method. Three different kinds of coaxial nozzles are employed to understand the flow physics involved in the supersonic coaxial jets. Two convergent-divergent supersonic nozzles are designed to have the same Mach number 2.0, and used to compare the coaxial jet flows with those discharging from one constant-area nozzle. The impingement angle of the annular jets are varied. The primary pressure ratio is changed in the range from 2.0 to 10.0 and the assistant jet ratio from 1.0 to 3.0. The results obtained show that the fluctuations of the total pressure and Mach number along the jet axis are much higher in the constant-area nozzle than those in the convergent-divergent nozzles, and the constant-area nozzle lead to higher total pressure losses, compared with the convergent-divergent nozzles. The assistant jets from the annular nozzle affect the coaxial jet flows within the distance less than about ten times the nozzle throat diameter, but beyond it the coaxial jet is conical with self-similar velocity profiles. Increasing both the primary jet pressure ratio and the assistant jet pressure ratio produces a longer coaxial jet core.
마이크로 초음속제트의 충돌유동과 레이저 가공 응용에 관한 연구
민성규(Seong-Kyu Min),유동옥(Dong-Ok Yu),이열(Yeol Lee),정조순(Jo-Soon Cheong) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.2
Characteristics of micro-sonic/supersonic axi-symmetric jet impinging on a flat plate with a pre-drilled hole were both experimentally and numerically studied, to observe the role of assist-gas jet to eject melted materials from the cut zone in the laser machining. For various Mach numbers of the nozzle and the total pressures of the assist gas, detailed impinging jet flow structures over the plate and the variations of mass flux through the pre-drilled hole were observed. It was found that the present experimental and numerical results show a good agreement, which proves the accountability of the present work. From the present study, it was also observed that the mass flow rate through the hole was closely related with the total pressure loss caused by the Mach disc on the work piece, and that supersonic nozzle could perform more efficient roles as blowing the assist-gas jet in the laser machining, as compared to sonic nozzles.
민성규(SeongKyu Min),유동옥(Dongok Yu),이열(Yeol Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Characteristics of micro supersonic jet impinging on a work-piece with a preset hole was experimentally investigated, to observe the role of the assist jet in the laser machining. The observed quantity includes the mass flow rate through the hole in the work-piece, presuming that high mass flux through it results in a high efficiency in the role of assist gas of laser machining. Effects of various parameters, such as nozzle Mach number, flow total pressure, on the mass flow rate through the hole have been observed. Present experimental results for the sonic micro-jet show a good agreement with the numerical/experimental results by previous investigators, and the new results for the supersonic micro-jet reveals that the assist gas issuing from a supersonic nozzle could provide a better efficiency in the laser machining process.
유동가시화 기법을 이용한 레이저가공의 보조가스 충돌특성에 관한 연구
손상혁(Sanghyuk Son),이열(Yeol Lee),민성규(Seongkyu Min) 대한기계학회 2011 大韓機械學會論文集B Vol.35 No.2
레이저가공에서 가공부위의 용융물질을 제거하는 보조가스의 역할을 살펴보기 위하여, 절단경사면에 충돌하는 초음속 동축/탈축노즐 유동의 특성이 실험적으로 관찰되었다. 보조가스의 압력, 노즐과 절단면과의 사이거리, 절단폭, 그리고 탈축노즐의 위치 등 다양한 관계변수의 변화에 대하여, 수백 개의 고해상도의 쉴러린 영상이 획득되었다. 그 결과, 단순한 보조가스의 증가가 절단면 하부에서 발생하는 유동박리를 제거하는데 효율적이지 않음이 관찰되었고, 절단폭의 증가와 탈축노즐의 운용으로 절단면에서의 박리현상을 경감시킬 수 있음이 확인되었다. 또한 음속노즐에 비하여 초음속노즐의 경우는 노즐출구와 가공면 사이의 사이거리가 절단면에서의 박리현상에 큰 영향을 미치지 않음이 관찰되었다. The characteristics of supersonic coaxial/off-axis jet impingements on a slanted kerf surface were experimentally studied, to investigate the role of the assist gas that removes molten materials from cut zone formed by laser machining. In this parametric study, hundreds of high-resolution schlieren images were obtained for various gas pressures, distances between nozzle exit and kerf surface, kerf widths, and alignments of off-axis nozzle. It was noticed that simply increasing the assist gas pressure was not effective in eliminating the flow separation that occurs downstream of the kerf surface. However, it was also observed that by increasing the kerf width and utilizing off-axis nozzles, the separation of the assist gas on the kerf surface can be weakened. The effect of the distance between the nozzle exit and the kerf surface on the characteristics of separation occurring on the kerf surface was found to be lower in the case of supersonic nozzles than that in the case of sonic nozzles.
초음속 사각노즐을 이용한 레이저가공 보조가스의 성능개선에 관한 연구
손상혁(SangHyuk Son),윤상훈(SangHun Yoon),전동연(DongYeon Jun),이열(Yeol Lee) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.4
레이저 절단가공에서 운용되는 보조가스의 충돌특성을 개선하기 위한 실험적 연구가 진행되었다. 보조가스의 압력, 노즐의 위치 및 각도 등 다양한 관계변수의 변화에 대하여, 초음속 사각노즐에서 분출되는 보조가스의 절단면 충돌특성이 기존의 원형단면의 노즐 경우와 비교 관찰되었다. 이를 위하여 쉴러린 유동가시화 및 절단면 후방에서의 피토압 측정이 진행되었다. 본 연구에서 응용된 사각 노즐의 경우, 동일한 노즐 출구 단면적을 갖는 기존의 원형노즐에 비하여 절단면을 따라 흐르는 보조가스의 박리현상을 약화시킬 수 있음이 확인되었다. An experimental study to improve the impingement-characteristics of assist gas in laser cutting was carried out. For various assist-gas pressures, locations and installation angles of the nozzle, the characteristics of impingement of the jet from a supersonic rectangular nozzle were compared to those previously observed for typical nozzles of circular cross-sectional exit, Schlieren flow visualizations and Pitot pressure measurements at the downstream of kerf surface were utilized for the purposes. The present rectangular supersonic nozzle that has the same cross-sectional exit area as a conventional circular nozzle was found to be able to weaken the separation of the assist gas on the kerf surface, as compared to the conventional circular nozzle.
레이저 가공에서 동축/탈축 보조가스의 충돌특성에 관한 수치해석적 연구
윤시경(Shi-Kyung Yoon),성홍계(Hong-Gye Sung),이열(Yeol Lee) 한국기계가공학회 2010 한국기계가공학회지 Vol.9 No.5
A computational study was carried out to analyze the characteristics of supersonic (Mach 2.0) coaxial/off-axis jet's impingements on a slanted kerf surface in laser machining. The effects of various parameters such as gas pressure, distance between nozzle exit and kerf edge surface, and application of off-axis nozzles on the impingement phenomena of the assist-gas on kerf surface were observed. The present study showed that simply increasing the assist-gas pressure for coaxial supersonic nozzle was not effective to alleviate the strength of flow separation on kerf surface. It also presented the optimized operating condition of the coaxial nozzle to have the highest skin friction values over kerf surface.
레이저 절단가공에서 노즐설계가 용융물질 제거에 미치는 영향에 관한 실험적 연구
손상혁(Sang-Hyuk Son),이석준(Seok-Joon Lee),이열(Yeol Lee) 한국기계가공학회 2012 한국기계가공학회지 Vol.11 No.1
An experimental study was carried out to observe the characteristics of impingement of assist gas from a rectangular supersonic nozzle on kerf surface in laser machining. A micro-scale supersonic (Mach number 2.0) rectangular nozzle system was designed and fabricated for the purposes, and hot tests of the performance of the nozzle system was proceeded in the ITI corporation laboratory. For various related parameters such as laser powers, nozzle pressures and cutting speeds, the quality of the frontal view of cut edge surfaces was observed by a microscope. In the study, it was shown that the application of the present micro-rectangular supersonic nozzle in an off-axis configuration made it possible to cut a mild steel, by combinations of relatively low laser - powers, large standoff distances, and assist gas with no oxygen, which was not achieved by conventional laser cutting processes.