• Title/Summary/Keyword: 진동제트

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A Study on Self-excitation in Laminar Lifted Coflow-jet Flames (층류 동축류 제트 부상화염에서의 자기진동에 관한 연구)

  • Van, Kyu Ho;Lee, Won June;Park, Jeong;Kim, Tae Hyung;Park, Jong Ho
    • Journal of the Korean Society of Combustion
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    • v.20 no.1
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    • pp.43-51
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    • 2015
  • A study on laminar jet flames in coflow air diluted with helium has been conducted to investigate self-excitations for various propane mole fractions and nozzle exit velocities. The stability map was represented as a function of nozzle exit velocity and fuel mole fraction for propane. The results show that two types of self-excitation were observed : (1) buoyancy-driven self-excitation (hereafter called BDSE) and (2) Lewis-number induced-self-excitation coupled with (1) (hereafter called LCB) near extinction limit for 9.4 mm nozzle diameter. It was shown that with 0.95 mm nozzle diameter, Lewis-number-induced self-excitation (hereafter LISE) and BDSE could be separated. The differences between the two self-excitations were shown and discussed.

Helieum-dilution Effect of Coflow Air on Self-excitation in Laminar Coflow Jet Flames (층류 동축류 제트에서 공기측 헬륨 희석이 화염진동에 미치는 영향)

  • Lee, Won June;Park, Jeong;Kwon, Oh Boong;Baek, Se Hyun;Ko, Sung Ho
    • Journal of the Korean Society of Combustion
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    • v.17 no.4
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    • pp.51-59
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    • 2012
  • Experimental study in coflow jet flames has been conducted to investigate the helium-dilution effect of coflow air on self-excitation. For various helium mole fractions and jet velocities, two types of self-excitation were observed: buoyancy-driven self-excitation and Lewis-number-induced self-excitation(here after called Le-ISE) coupled with buoyancy-driven one. The difference between buoyancy-driven and Le-ISE is clarified by using the Mie-scattering visualization as well as exploring the different features. The mechanism of Le-ISE is proposed. When the system Damk$\ddot{o}$hler number was lowered, Le-ISE is shown to be launched. Le-ISE is closely related to heat loss, in that it can be launched in even methane jet flame (Lewis number less than unity) with helium-diluted coflow air. Particularly, Le-ISE becomes significant as the Damk$\ddot{o}$hler number decreases and heat-loss becomes significant.

OH-and CH-Radical Chemiluminescence Characteristics in the Spray Combustion of Ultransonically Atomized Kerosene (초음파에 의해 무화된 케로신 분무연소에서의 OH 라디칼 및 CH 라디칼 자발광 특성)

  • Kim, Min Cheol;Kim, Jeong Soo
    • Journal of the Korean Society of Propulsion Engineers
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    • v.22 no.1
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    • pp.72-79
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    • 2018
  • An experimental study was performed to investigate the chemiluminescence characteristics in the spray combustion of ultransonically atomized kerosene. The radical intensity of the spray flame was measured using an ICCD camera and the amount of fuel consumed was obtained by a precise flow-rate measurement technique during combustion. Fuel consumption increased linearly with the increase in carrier-gas flow rate, and typical group combustion, which is a characteristic of spray combustion, was observed. It was found from the analysis of chemiluminescence that the maximum emission intensities of OH and CH radicals decrease, and they move downstream resulting in the increase in a vivid reaction zone as the spray flow rate increases.

Effect of Coflow Air Velocity on Heat-loss-induced Self-excitation in Laminar Lifted Propane Coflow-Jet Flames Diluted with Nitrogen (질소로 희석된 프로판 동축류 층류 제트 부상화염에서 열손실에 의한 자기진동에 대한 동축류 속도 효과)

  • Lee, Won-June;Yoon, Sung-Hwan;Park, Jeong;Kwon, Oh-Boong;Park, Jong-Ho;Kim, Tae-Hyung
    • Journal of the Korean Society of Combustion
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    • v.17 no.1
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    • pp.48-57
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    • 2012
  • Laminar lifted propane coflow-jet flames diluted with nitrogen were experimentally investigated to determine heat-loss-related self-excitation regimes in the flame stability map and elucidate the individual flame characteristics. There exists a critical lift-off height over which flame-stabilizing effect becomes minor, thereby causing a normal heat-loss-induced self-excitation with O(0.01 Hz). Air-coflowing can suppress the normal heat-loss-induced self-excitation through increase of a Peclet number; meanwhile it can enhance the normal heat-lossinduced self-excitation through reducing fuel concentration gradient and thereby decreasing the reaction rate of trailing diffusion flame. Below the critical lift-off height. the effect of flame stabilization is superior, leading to a coflow-modulated heat-loss-induced self-excitation with O(0.001 Hz). Over the critical lift-off height, the effect of reducing fuel concentration gradient is pronounced, so that the normal heat-loss-induced self-excitation is restored. A newly found prompt self-excitation, observed prior to a heat-loss-induced flame blowout, is discussed. Heat-loss-related self-excitations, obtained laminar lifted propane coflow-jet flames diluted with nitrogen, were characterized by the functional dependency of Strouhal number on related parameters. The critical lift-off height was also reasonably characterized by Peclet number and fuel mole fraction.

A Comparative Study Between Diffusive-thermal and Buoyancy-driven Self-excitations in Laminar Free Jet Flames with Applied DC Electric Fields (직류전기장이 인가된 층류제트화염에서 물질 -열 확산과 부력에 의한 진동비교에 관한 연구)

  • Han, Jong-Kyu;Yoon, Sung-Hwan;Park, Jeong;Kwon, Oh-Boong;Kim, Tae-Hyung;Park, Jong-Ho
    • Journal of the Korean Society of Combustion
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    • v.17 no.1
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    • pp.37-47
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    • 2012
  • Experimental study on comparison of diffusive-thermal self-excitation with buoyancy-driven one due to accumulation of partially premixed, preheated mixture in front of edge flame was conducted in horizontally and vertically injected laminar free-jet flames with an applied DC electric field of -10 kV. The application of horizontal injection method with the DC electric field to jet flames was experimentally designed to suppress heat-loss-induced self-excitation and thereby to highlight the definite difference between both diffusive-thermal and buoyancy-driven self-excitations with the same order of O(1.0 Hz), in that diffusive-thermal self-excitation has not been so far found experimentally in laminar jet flames. Flame stability maps in vertically and horizontally injected jet flames are presented. The distinct modes of individual self-excitation are shown to be well described by their own phase diagrams. The results show that buoyancy-driven self-excitation due to the accumulation of partially premixed, preheated mixtures in front of edge flame is branched from the buoyancy-induced self-excitation with O(10 Hz) due to a flame flicker. Once the buoyancy-driven self-excitation appears, it suppresses buoyancy-induced as well as diffusive-thermal self-excitation. The key characteristics for individual self-excitation are discussed and their functional dependencies of Strouhal number upon related physical parameters are also presented.

A Combustion Characteristics of Attached Jet Flame under the Regular Oscillation (규칙적인 진동 하에서 노즐 부착된 제트화염의 연소특성)

  • Kim, Dae-Won;Lee, Kee-Man
    • Fire Science and Engineering
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    • v.23 no.1
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    • pp.55-62
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    • 2009
  • A general combustion characteristics of forcing nonpremixed jet in laminar flow rates have been conducted experimentally to investigate the effect of forcing amplitude with the resonant frequency of fuel tube. There are two patterns of the flame lift-off feature according to the velocity increasing; one has the decreasing values of forcing amplitude on the lift-off occurrence when a fuel exit velocity is increasing, while the other has the increasing values. These mean that there are the different mechanisms in the lift-off stability of forced jet diffusion flame. Especially, the characteristics of attached jet flame regime are concentrically observed with flame lengths, shapes, flow response and velocity profiles at the nozzle exit as the central figure. The notable observations are that the flame enlogation, in-homing flame and the occurrence of a vortical motion turnabout have happened according to the increase of forcing amplitude. It is understood by the velocity measurements and visualization methods that these phenomena have been relevance to an entrainment of surrounding oxygen into the fuel nozzle as the negative part of the fluctuating velocity has begun at the inner part of the fuel nozzle.

Separation control using multi-array/multi-location synthetic jet (Multi-array/multi-location synthetic jet을 이용한 박리 제어)

  • 김상훈;김종암
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.34 no.8
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    • pp.8-15
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    • 2006
  • Separation control has been performed using the multi-array/multi-location synthetic jet on NACA23012 at high angle of attack. The flow control using single synthetic jet shows that stall characteristics can be substantially improved with delayed separation point. Theses results show the characteristic of unsteady flow of single synthetic jet. Beside, we researched on multi-array synthetic jet to obtain applicable synthetic jet velocity. Multi-location synthetic jet is proposed to eliminate small vortex on suction surface of airfoil. With the results, we concluded that the flow around airfoil is stable by high frequency synthetic jet with elimination of small vortex and confirmation of stable flow. Moreover, performance of multi-array/multi-location synthetic jet can be improved by changing phase angle of multi-location synthetic jet.

Analysis of Flow and Pressure Downstream of a Weir using Image Technique (영상기법을 활용한 보 하류의 흐름 및 압력특성 분석)

  • Ryu, Young-Uk;Park, Moonhyung;Kim, Hyung Suk;Choi, Seo Hye
    • Proceedings of the Korea Water Resources Association Conference
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    • 2017.05a
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    • pp.511-511
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    • 2017
  • 하천에서 홍수 예방 및 가뭄재해 방지를 목적으로 최근 4대강 살리기 사업이 수행되었다. 특히, 안정적인 용수공급 및 다양한 수재해 피해를 최소화하기위해 다기능보가 설치되었다. 설치된 보는 고정보와 가동보로 구분되며 평상시에는 고정보를 넘어가는 월류흐름이 발생하며 홍수 시에는 추가적으로 가동보를 개방하여 오리피스 흐름이 발생한다. 최근 기후변화로 인해 집중호우가 빈번히 발생하며 이는 보 주변에서 빠르고 복잡한 흐름을 유발하게 된다. 이러한 흐름특성은 보하류의 세굴문제뿐만 아니라 물받이와 바닥보호공의 안전성에 영향을 미칠 수 있다. 본 연구에서는 영상기법을 활용하여 도수가 발생하는 조건에서 고정보 하류의 물받이공 및 바닥보호공에 난류흐름특성 및 압력분포를 분석하였다. 길이 8.0 m, 폭 0.3 m를 갖는 개수로에서 실험을 수행하였으며 0.2 m 높이의 고정보는 상류경계로부터 3.0 m지점에 위치하였다. 보 하류부에서 유속성분은 비접촉식 유속측정 기법인 입자영상유속계(Particle Image velocimetry, PIV)와 기포흐름을 측정할 수 있는 기포영상유속계(Bubble Image velocimetry, BIV)를 적용하였다. 그러므로 기포 존재유무와 관계없이 보 하류부 구간에 대한 유속장 성분을 취득하였다. 도수흐름은 물받이공 및 바닥보호공 영역의 바닥면을 따라 빠른 유속을 갖는 제트류가 발생하고 수면과 바닥으로 강한 진동이 발생하여 불안정한 흐름이 야기된다. 바닥면에 작용하는 압력을 측정하기 위해 흐름방향을 따라 피에조미터를 설치하였고 압력수두 분포를 초고속카메라로 촬영하여 그 특성을 분석하였다. 실험을 결과를 통해 보 하류부에 영향을 미치는 인자를 도출하였으며 향후 보 설계기준에 반영할 수 있을 것으로 기대된다.

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축소 노즐에서의 슬롯 막냉각 열전달 특성에 관한 연구

  • 조용일;조형희
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2000.04a
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    • pp.33-33
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    • 2000
  • 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. 따라서 본 연구에서는 실험을 통하여 면적비가 16:1인 축소노즐에서 압축성 효과를 배제할 수 있는 유동속도 범위 내에서 분사율 변화(0.5 $\leq$ M $\leq$ 3.0)에 따른 슬롯 막냉각 열전달 특성을 고찰하고, 평판 슬롯 막냉각 경험식의 결과와 비교하였으며, 수치해석을 통하여 축소노즐과 원형관에서의 냉각효율 및 열전달 특성을 비교함으로서 이를 검증하였다. 축소노즐에서의 슬롯 막냉각 열전달 특성은 단열벽면조건을 형성하여 노즐 표면을 따라 설치된 열전대를 이용하여 측정하였다. 그 결과 상대적으로 낮은 분사율(M=0.5, 1.0)에서 분사율 증가에 따른 냉각효율의 증가가 크게 나타났으며, 분사율이 높아짐(M $\geq$ 2.0)에 따라 냉각효율의 증가폭이 점점 감소하고, 일정 분사율 이상에서는 냉각 효율의 증가가 크게 둔화되었다. 분사율이 낮을 경우 평판 슬롯 막냉각 경험식으로 주어진 결과보다 상류에서는 높으나 하류로 진행하면 비슷한 냉각효율을 보였고, 분사율이 높은 경우 평판보다 전 범위에서 약간 높은 냉각효율을 나타냈다. 수치해석 결과에서는 분사율이 낮을 경우 축소노즐의 냉각효율이 원형관에서의 냉각효율 보다 낮거나 비슷하게 나타났으며, 분사율이 높아짐에 따라 축소노즐에서의 냉각효율이 오히려 높아지는 것으로 나타났다.타내었다. 액체 제트의 속도는 처음에는 일정하게 유지되다가 운동량을 보존하기 위해 가스로부터 운동량을 받아 점차 가속되어지는 것으로 나타났다.본 규격은 키, 총장, 어깨길이, 등길이, 머리길이, 머리둘레, 진동둘레, 목둘레, 가슴둘레, 허리둘레, 배둘레, 엉덩이둘레, 앞품, 뒤품, drop치를 포함하고 있고, 각 규격에서 호칭간 치수 간격도 함께 제시하고 있다. 본 연구 결과에서 보듯, 현행 8규격의 무진복의 각 호칭간 적정 허용범위를 고려해 합리적인 치수체계를 정립한다면 치수에 대한 적합도가 상당히 증가할 뿐 아니라 생산비용도 상당히 감축할 것으로 생각된다.나타났다. 4) 호감적 서비스능력 차원에서 세 독립변수간에 유의한 3원 상호작용이 존재하는 것으로 나타나( $F_{2,228}$=15.62, P<.001) 20대에 적합한 의복 착용시( $F_{2,228}$=3.98, P<.05)와 60대에 적합한 의복 착용시( $F_{2,228}$=16.55, P<.001) 점포유형과 격식차림간에는 유의한 상호작용이 존재하는 것으로 나타났다. 5) 호감을 구성하는 세 요인들이 구매의도에 미치는 영향을 조사한 결과 호감적 인상차원은 29%(P<.001), 호감적 서비스능력차원은 6%(P<.001)의 구매의도를 설명해 주는 것으로 나타났다. 본 연구결과 노년 소비자에게 호감을 주는 판매원의 외모는 구매의도에 영향을 주어 실버의류산업의 이익증대와 밀접한 연관을 갖는 서비스품질의 중요한 요인으로 밝혀졌다.중요한 요인으로 밝혀졌다.로운 단백질 EPSPS가 다른 여러 식물에 이미 존재하고 있는 단백질로서 우리가 이미 이러

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A Study on the Selection of Hydrogen Refueling Station Locations within Military Bases Considering Minimum Safe Distances between Adjacent Buildings (인접 건물 간 최소 안전거리를 고려한 군부대 내 수소충전소 위치선정 연구)

  • Dong-Yeon Kim;Hyuk-Jin Kwon
    • Journal of Internet Computing and Services
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    • v.24 no.6
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    • pp.171-180
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    • 2023
  • Hydrogen energy technology is gaining importance in the era of the Fourth Industrial Revolution, offering military advantages when applied to military vehicles due to its characteristics such as reduced greenhouse gas emissions, noise, and low vibration. Korea's military has initiated the Army Tiger 4.0 plan, focusing on hydrogen application, downsizing, and AI-based smart features. The Ministry of National Defense plans to collaborate with the Ministry of Environment to expand hydrogen charging stations nationwide, anticipating increased deployment of military hydrogen vehicles. However, considering the Jet Fire and VCE(Vapor Cloud Explosion) nature of hydrogen, ensuring safety during installation is crucial. Current military guidelines specify a minimum safety distance of 2m from adjacent buildings for charging stations. Scientific methods have been employed to quantitatively assess the accident damage range of hydrogen, proposing a minimum safety distance beyond the affected area.