스크램제트 엔진의 모드천이 발생동안 의사충격파 유동에 관한 연구

하정호(Jeong Ho Ha),Foluso Ladeinde,김희동(Heuy Dong Kim) 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.12

이중 모드 스크램제트는 일반적으로 기류 마하수 3-6의 범위에서 작동한다. 이중 모드 스크램제트가 작동하는 동안 램제트 모드에서 스크램제트 모드로의 천이 혹은 그 반대의 경우가 불가피하다. 스크램제트 모드에서 연소실의 상류에서는 초음속 영역이 형성이 되며, 이와 같은 유동은 일반적으로 낮은 당량비에서 얻을 수 있다. 엔진의 입구의 전온도가 일정한 경우 당량비가 증가할수록 벽면의 경계층과의 간섭작용에 의해 강한 충격파가 발생해 연소실의 상류는 아음속이 된다. 이 같은 모드 천이는 당량비에 따른 충격파의 비정상 유동 특성과 관련이 있다. 본 연구에서는, 모드 천이가 발생하는 동안 발생하는 상세한 유동 특성을 조사하기 위해 이론해석과 수치해석을 수행하였다. 얻어진 결과로부터 모드 천이는 급격하게 발생한다는 것을 보여준다. Dual mode scramjet is typically operated in a range of M∞= 3 to 6. During operation of dual mode scramjet, transition from ramjet to scramjet and vice-versa is inevitable. In a scramjet mode, the supersonic flow field is formed upstream of combustor, thus having the combustion at a supersonic flow circumstance. Such a flow is typically obtained at a low equivalent ratio. As the equivalent ratio is increasing for a given constant total temperature at the inlet of engine, a shock train is formed due to strong interaction with the wall boundary layer, leading to subsonic combustion. This mode transition is associated with the unsteady behaviors of shock train according to the equivalent ratio at constant inlet total temperature. In the present study, theoretical and computational analyses have been applied to investigate the detailed flow field generating during the mode transition. The obtained results showed that the mode transition does not occur in a gradual process but in a sudden discontinuous variation, leading to having a non-allowable region during the transition.

스크램제트 엔진에서의 모드 천이에 관한 수치해석 연구

하정호,Rajarshi Das,폴루소 라덴데,김태호,김희동 한국추진공학회 2017 한국추진공학회지 Vol.21 No.6

In the present study, theoretical and numerical analyses have been carried out to investigate the detailed flow characteristics during the mode transition. The theoretical analysis rearranged the knowledge of gasdynamics and the previous studies, and the numerical analysis has conducted to solve the 2D unsteady compressible Navier-Stokes equations with a fully implicit finite volume scheme. To validate the numerical analysis, the experiment was compared with it. The total temperature at the inlet of isolator and the hydrogen fuel equivalent ratio were changed to investigate their effects on the mode transition phenomenon. As the results, the numerical analysis reproduced well the experiment qualitatively, the increment in the hydrogen fuel equivalent ratio induced the scram-mode to ram-mode transition which is discontinuous with a non-allowable region, and the variation in the total temperature changed the boundary of the mode transition. 본 연구에서는 모드 천이가 발생하는 동안 상세한 유동 특성을 조사하기 위해, 이론분석과 수치해석을 수행하였다. 이론분석은 기존의 기체역학과 종래 보고된 이론식들 재정립하였으며, 수치해석은 2차원 비정상 압축성 Navier-Stokes 방정식을 풀기 위해 fully implicit finite volume scheme을 사용해 수행하였다. 해석의 검증을 위하여 실험 결과와 비교하였다. 격리부 입구 전온도와 수소 연료의 당량비를 변화시키면서 모드 천이에 미치는 영향을 조사하였다. 해석과 실험 결과는 정성적으로 잘 일치하였다. 당량비가 증가하면 스크램제트 모드에서 램제트 모드로 천이가 발생하였다. 이 때, 천이는 당량비에 따라 불연속적으로 나타나며, Non-allowable region이 존재하였다. 한편 격리부 입구에서 전온도의 증가는 모드 천이 경계를 변화시켰다.

스크램제트 엔진의 모드 천이에 관한 연구

하정호(Jeong Ho Ha),Foluso Ladeinde,김희동(Heuy Dong Kim) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12

Dual mode scramjet is typically operated in a range of M<SUB>∞</SUB>= 3 to 6. During operation of dual mode scramjet, transition from ramjet to scramjet and vice-versa is inevitable. In a scramjet mode, the supersonic flow field is formed upstream of combustor, thus having the combustion at a supersonic flow circumstance. Such a flow is typically obtained at a low equivalent ratio. As the equivalent ratio is increasing for a given constant total temperature at the inlet of engine, a shock train is formed due to strong interaction with the wall boundary layer, leading to subsonic combustion. This mode transition is associated with the unsteady behaviors of shock train according to the equivalent ratio at constant inlet total temperature. In the present study, theoretical and computational analyses have been applied to investigate the detailed flow field generating during the mode transition. The obtained results showed that the mode transition does not occur in a gradual process but in a sudden discontinuous variation, leading to having a non-allowable region during the transition.

An Application of a Link-Based Optimal Pathfinding Algorithm with the Integrated Transit Network from Smart Card Systems

이미영,이창주 대한토목학회 2020 KSCE Journal of Civil Engineering Vol.24 No.11

With the spread of information technology in the transportation field, many cities around the globe have introduced smart card systems to stimulate the use of transit services. The systems have resulted in not only the improvement of users’ convenience but also the dramatic changes of travel behaviors with transit services. One prevailing phenomenon is the user’s perception for all transit modes as one single mode in the integrated transit network because of seamless services provided by smart card systems. Although this change has brought tremendous advantages to the dynamics of transit services, it has become more complicated to understand travel behaviors in the integrated transit network which includes features of transfers, service schedule, waiting time and fares. Given that smart card systems have affluent information which can reflect such characteristics, their proper utilizations are still in question. In this sense, when compared with a single-mode network, specific approaches need to be considered to build an integrated transit network from smart card systems, and to develop a suitable model that can reflect the features of the integrated transit network. With smart card systems in the greater Seoul area, Korea, this research proposes methodological techniques which can create the integrated transit network and facilitate transfers automatically between modes. In addition, an attempt is made to verity the applicability of a link-based optimal pathfinding algorithm that has been spotlighted to consider complex travel behaviors in a transit network but has not been proven in the integrated transit network from smart card systems. The concepts of mode-based link labeling and “big node” for transfers are employed with this algorithm. From their applications, optimal transit paths are successfully searched by proposed concepts with smart card data. Given that building an integrated transit network and finding optimal paths are essential tasks for transit analysis studies, this research provides irreplaceable contributions to utilize link-based optimal pathfinding algorithms in the integrated transit network with smart card systems.

넓은 입출력 전압을 위한 LLC 공진형 컨버터의 풀 브리지-하프 브리지 모드 변환 기법 연구

최민영,백승우,김학원,조관열,강정원 전력전자학회 2022 전력전자학회 논문지 Vol.27 No.4

This paper presents a mode transition method that applies frequency compensation technique of an LLC resonant converter for stable mode transition. LLC resonant converters used in various applications require high efficiency and high power density. However, because of circuit property, a wider voltage gain range equates to a greater circuit loss, so maintaining high efficiency at all voltage gain ranges is difficult. In this case, full bridge-half bridge mode transition method can be used, which maintains high efficiency even in a wide voltage gain range. However, this method causes damage to the circuit through overcurrent by the mode transition. This study analyzes the cause of the problem and proposes a mode transition method that applies frequency compensation technique to solve the problem. The proposed method verifies the stable transition through simulation analysis and experimental results.

Influence of helium metastable states on the E-H mode transition in an inductively coupled plasma

Lee Wonwook,Shim Sungyong,Oh Cha-Hwan 한국물리학회 2022 Current Applied Physics Vol.36 No.-

A helium (He) inductively coupled plasma (ICP) source combined with two diode laser systems with the wavelengths of 396.5 nm (21 S–41 P) and 1082.9 nm (23 S–23 P) was configured to investigate the influence of He metastable states on the E-H mode transition. The population densities of 21 S and 23 S states were measured by laser absorption spectroscopy as the functions of RF power, He pressure, and the distance from RF antenna. Correlations between the E-H mode transition and the population density ratio of the 23 S metastable state to the 21 S metastable state as well as the line intensity ratio (LIR) of the 33 D-23 S transition to the 31 P–21 S transition were investigated. The E-H mode transition of He ICP was analyzed by the electron impact ionization rate and it was confirmed that the 23 S metastable state plays a key role in the E-H mode transition.

A study on the E-H mode transition with the line integrated He 23S metastable atom density in an inductively coupled plasma

심성용,이원욱,박진우,오차환 한국물리학회 2021 Current Applied Physics Vol.28 No.-

Helium (He) inductively coupled plasma (ICP) was generated by a right-helical-type RF antenna. At a fixed He pressure of 20 mTorr, the optical emission spectrum from the He plasma was measured with RF power. The E-H mode transition and the characteristic hysteresis of the mode transition were confirmed by a change in the spectral line intensity of the 33D 23P transition at 587.6 nm. By laser absorption spectroscopy using a laser light with a wavelength of 1083 nm resonant to the 23S→23P absorption transition, the line-integrated He 23S metastable density was measured and found to show consistent behavior with the spectral line intensity of the 33D 23P transition during the E-H mode transition. The line-integrated He 23S metastable atom density exhibited distinctly different longitudinal distributions in the E and H modes.

SEM Tribosystem에 의한 TiN피막의 미시적 마모형태의 천이 조건

문봉호(Bong-Ho Moon) 한국기계가공학회 2011 한국기계가공학회지 Vol.10 No.3

To evaluate the wear characteristics of very thin ceramic coated layer, it is very important to investigate its wear process in great detail. An effective method for investigating the wear of a thin layer is the observation of wear process in microscopic detail, using in-situ system. In this study, based on the SEM Tribosystem as in-situ system, the microscopic wear mode of TiN coatings was investigated in repeated sliding. Consequently, four modes were revealed for TiN coatings: Ploughing, powder formation, flake formation and coating delimitation. Sc(Severity of contact) can clarify transition condition of those microscopic wear modes.

A mode transition strategy from air to oxyfuel combustion in a 35MW coal-fired power plant boiler

Zixue Luo,Wenfeng Cheng,Bo Wu,Yongchun Zhao,Junying Zhang 한국화학공학회 2017 Korean Journal of Chemical Engineering Vol.34 No.5

The atmosphere under the conditions of a coal combustion reaction in the furnace is the factor that makes the most significant difference during mode transition from traditional air to oxy-fuel combustion. The flue gas is adopted as the primary air and secondary air for pulverized-coal conveying and the support of combustion; it has a high carbon dioxide concentration during the oxy-fuel combustion. The air-leakage reduces CO2 enrichment and leads to thermal NOx production. A control strategy of this shift operation is conducted in a 35MW oxy-fuel combustion power plant boiler by adjusting the furnace pressure, regulating the recirculation rate of the flue gas and amending the oxygen concentration in the inlet stream. The furnace pressure can be changed smoothly and stabilized at a micro-positive level as the pressurized air flow is monitored at a suitable range. The combustion-supporting flue gas is modified by the oxygen content in the furnace outlet, and the circulation rate of the flue gas verifies the regulation process. Results show that the CO2 concentration in the flue gas can be rapidly increased along with the increment of furnace pressure and oxygen in the inlet stream; then, this procedure gradually becomes flattened. The CO2 content in the flue gas correlates with the recirculation rate of the flue gas and oxygen concentration in the inlet stream. The two operation parameters should be maintained at a high CO2 concentration in a range from 0.6-0.7 and 29.5%-30.5%, respectively. Sampling analysis shows that SO2 and NOx emissions were 26 (±1.5) mg/MJ and 90 (±11.7) mg/MJ in air condition, 14 (±0.4) mg/MJ and 34 (±1.6) mg/MJ in oxy-fuel combustion; the burnout rate, mechanical losses of incomplete combustion and the unburned carbon rate remained similar at these two stable combustion modes. This mode transition scheme should provide a reference for monitoring and diagnostics, design and operation control of an oxygen-enriched pulverized-coal combustion power plant boiler.

Half-Mode Substrate Integrated Waveguide Amplifier Using Lumped-Element Transition

Dong-Sik Eom,Hai-Young Lee 한국전자파학회JEES 2017 Journal of Electromagnetic Engineering and Science Vol.17 No.1

This paper proposes a half-mode substrate integrated waveguide (HMSIW) amplifier using lumped-element transition. The input and output impedances of this amplifier are matched by the lumped-element transition structure. This structure provides compact impedance and mode matching circuits between the HMSIW and a stand-alone amplifier. Surface mount technology inductors and capacitors are implemented to realize the lumped-element transition. A prototype of the proposed HMSIW amplifier shows 15 dB gain with 3 dB bandwidth of 4 to 7.05 GHz in a simulation and measurement.