A Numerical Analysis of Supersonic Intake Buzz in an Axisymmetric Ramjet Engine

Hyo-Won Yeom,Hong-Gye Sung,Vigor Yang 한국항공우주학회 2015 International Journal of Aeronautical and Space Sc Vol.16 No.2

A numerical analysis was conducted to investigate the inlet buzz and combustion oscillation in an axisymmetric ramjet engine with wedge-type flame holders. The physical model of concern includes the entire engine flow path, extending from the leading edge of the inlet center-body through the exhaust nozzle. The theoretical formulation is based on the Farve-averaged conservation equations of mass, momentum, energy, and species concentration, and accommodates finite-rate chemical kinetics and variable thermo-physical properties. Turbulence closure is achieved using a combined scheme comprising of a low-Reynolds number k-ε two-equation model and Sarkar’s compressible turbulence model. Detailed flow phenomena such as inlet flow aerodynamics, flame evolution, and acoustic excitation as well as their interactions, are investigated. Mechanisms responsible for driving the inlet buzz are identified and quantified for the engine operating at subcritical conditions.

A Numerical Analysis of Supersonic Intake Buzz in an Axisymmetric Ramjet Engine

Yeom, Hyo-Won,Sung, Hong-Gye,Yang, Vigor The Korean Society for Aeronautical and Space Scie 2015 International Journal of Aeronautical and Space Sc Vol.16 No.2

A numerical analysis was conducted to investigate the inlet buzz and combustion oscillation in an axisymmetric ramjet engine with wedge-type flame holders. The physical model of concern includes the entire engine flow path, extending from the leading edge of the inlet center-body through the exhaust nozzle. The theoretical formulation is based on the Farve-averaged conservation equations of mass, momentum, energy, and species concentration, and accommodates finite-rate chemical kinetics and variable thermo-physical properties. Turbulence closure is achieved using a combined scheme comprising of a low-Reynolds number k-${\varepsilon}$ two-equation model and Sarkar's compressible turbulence model. Detailed flow phenomena such as inlet flow aerodynamics, flame evolution, and acoustic excitation as well as their interactions, are investigated. Mechanisms responsible for driving the inlet buzz are identified and quantified for the engine operating at subcritical conditions.

Morphology, electrical conductivity, and rheology of latex-based polymer/nanocarbon nanocomposites

장건수,Hyo Yeol Yeom,Ju Won Park,Song Hee Lee,이성재 한국유변학회 2021 Korea-Australia rheology journal Vol.33 No.4

Nanocarbon materials are critical ingredients with unique properties in emerging materials. In this study, various carbon nanofillers, such as carbon nanotube (CNT), graphene oxide (GO), reduced GO wrapped by poly(styrene sulfonate) (PSS-RGO), and graphite nanoplatelet (GNP), were utilized to examine the effects of nanofiller types and surface treatments on the electrical and rheological properties of polystyrene (PS) nanocomposites prepared by latex-based process. The PS/CNT nanocomposites exhibited the most enhanced electrical and rheological properties among the composites evaluated. The PS/GO nanocomposites showed improved rheological properties and significantly increased electrical conductivity, despite the decrease in the intrinsic properties of graphene due to the change in hybridization from sp2 to sp3 by strong acid treatment. Interestingly, they exhibited higher conductivity than PS/PSS-RGO due to the higher graphene moiety and the thermal reduction of GOs during compression molding. The PS/GNP nanocomposites showed marginal enhancement because GNP is a larger aggregate of graphene layers bonded by van der Waals force. The results of this study on the electrical and rheological properties, surface modification, and size and dispersion of conductive nanofillers in an insulating polymer matrix are beneficial for the development and application of electrically conductive nanocomposites.

Developing a dynamic portfolio selection model with a self-adjusted rebalancing method

Jung, Jongbin,Kim, Seongmoon Informa UK (TaylorFrancis) 2017 JOURNAL OF THE OPERATIONAL RESEARCH SOCIETY - Vol.68 No.7

라텍스 기법에 의한 폴리스티렌/그래핀 나노필러 나노복합재료의 제조 및 물성

염효열(Hyo Yeol Yeom),나효열(Hyo Yeol Na),정대원(Dae-won Chung),이성재(Seong Jae Lee) 한국고분자학회 2015 폴리머 Vol.39 No.3

고분자 재료에 전기 전도성을 부여하기 위해 그래핀 기반의 나노필러를 도입하여 전도성 나노복합재료를 제조하였다. 그래핀 나노필러는 폴리스티렌(PS) 입자와 수계 분산이 용이하도록 산화 그래핀(GO) 및 poly(styrene sulfonate)가 도포된 환원된 산화 그래핀(PSS-RGO)을 사용하였다. GO는 흑연으로부터 modified Hummers 방법으로 합성하였으며, PSS-RGO는 GO가 분산된 PSS 용액을 hydrazine monohydrate로 환원시켜 제조하였다. 라텍스 기법으로 제조한 PS/GO 및 PS/PSS-RGO 나노복합재료의 모폴로지, 유변물성 및 전기적 물성을 고찰하였다. GO 및 PSS-RGO 나노필러는 PS 매트릭스 내에 잘 분산된 모폴로지를 보여 주었다. 그래핀 나노필러 함량에 따른 유변학적, 전기적 임계점은 GO가 0.28, 0.51 wt%로 나타났고 PSS-RGO는 0.50, 1.01 wt%로 나타났다. PS/GO 나노복합재료가 우수한 전기 전도도를 보여주는 이유는 성형시의 열처리에 의해 GO가 환원되어 전기적 물성을 부분적으로 회복했기 때문으로 판단된다. Electrically conductive polymer nanocomposites were prepared by the inclusion of graphene-based nanofillers. Graphene oxide (GO) and reduced graphene oxide wrapped by poly(styrene sulfonate) (PSS-RGO) were used as nanofillers to make good dispersion with the aqueous dispersion of polystyrene (PS) particles. GO sheets were synthesized by the modified Hummers" method from graphite, and PSS-RGO sheets were prepared by the reduction of GO-dispersed PSS solution with hydrazine monohydrate. Morphology and properties of PS/GO and PS/PSS-RGO nanocomposites via latex technology were investigated. Both nanofillers showed well dispersed morphology in PS matrix. Rheological and electrical percolation thresholds were 0.28 and 0.51 wt% for GO, and 0.50 and 1.01 wt% for PSS-RGO respectively. It is speculated that PS/GO nanocomposites showed better conductivity than PS/PSS-RGO counterparts due to the partial recovery of GO by thermal reduction during molding.

초음속 엔진의 흡입구 종말충격파와 연소실 화염의 상호간섭 동적연구

염효원(Hyo-Won Yeom),김선경(Sun-Kyeong Kim),김성진(Seong-Jin Kim),성홍계(Hong-Gye Sung),길현용(Hyun-Yong Gil),윤현걸(Hyun-Gull Yoon) 한국추진공학회 2009 한국추진공학회 학술대회논문집 Vol.2009 No.5

초음속 엔진의 흡입구에서의 종말충격파와 연소실 화염의 상호간섭 연구를 위하여 초음속 엔진의 전 영역, 즉 흡입구에서부터 연소실과 노즐까지 통합하여 비정상 연소수치해석을 수행하였다. 초음속 엔진이 상승하는 가속모드와 순항모드에서 상호간섭의 동적현상을 연구하였다. 흡입구에서의 충격파거동과 주요 위치에서 압력거동을 분석하고 초음속 엔진 전영역에서의 음향모드를 분석하여 현 시스템의 동적 거동을 파악하였다. Unsteady numerical analysis of an entire supersonic propulsion system from intake to nozzle was performed to study dynamic interaction between terminal shock in the intake and flame in the combustor. Both acceleration and cruise flight-modes were considered. Acoustic mode of the entire engine for both fligh- modes were investigated by detail analysis of pressure fluctuation at each location of engine.

이중연소 램제트의 혼합/연소 해석을 위한 Delayed Detached-Eddy Simulation

염효원(Hyo-Won Yeom),서봉균(Bong-Gyun Seo),성홍계(Hong-Gye Sung),길현용(Hyun-Young Gil),윤현걸(Hyun-Gul) 한국추진공학회 2012 한국추진공학회 학술대회논문집 Vol.2012 No.11

이중연소 램제트는 두 개의 연소기(아음속 연소기와 초음속 연소기)로 이루어져 있다. 본 논문은 초음속 연소기에서의 혼합 연소 특성을 살펴 보기위하여 하이브리드 기법인 delayed detached-eddy simulation(DDES) 수치 기법을 연구하였다. Reynolds average 형태의 난류 모델 중 초음속 유동해석에서 널리 애용되는 k-w SST 모델 결과와 비교하였다. 스플리터와 연소기에서의 충력파의 구조와 두 초음속 유동의 혼합 및 연소특성을 살펴보고 연소기의 팽창비의 영향을 조사하였다. Dual combustion ramjet has two combustors of subsonic and supersonic combustors. The mixing and combustion characteristics in the supersonic combustor are investigated using hybrid turbulence technique, delayed detached-eddy simulation(DDES). The evaluation was performed with the results of k-w SST model which commonly applied for supersonic turbulent flow. analysis The shock wave structures, mixing and combustion characteristics are addressed and the expansion ratios of combustor area has been investigated.

편백정유향 흡입이 대학생의 스트레스 및 우울에 미치는 영향

이효은(Hyo eun Lee),신원섭(Won sop Shin),연평식(Poung Sik Yeoun),조영민(Young Min Cho),염상희(Sang Hee Yeom) 한국산림휴양학회 2011 한국산림휴양학회지 Vol.15 No.2

본 연구는 진로나 직업에 대한 고민으로 인한 스트레스에 노출된 대학생을 대상으로 편백정유를 이용한 향기요법이 스트레스 및 우울감 감소에 긍정적인 효과가 있는지를 알아보고자 실시한 실험이었다. 이 실험은 총 20명을 대상으로 실험군과 대조군으로 구분하여 실험군은 편백정유를 대조군은 변성알콜을 4주간(28일) 동안 램프확산법을 이용하여 취침 중 자연스럽게 편백정유향을 후각에 노출시켜 스트레스 및 우울감의 사전과 사후의 차이를 알아보았다. 그 결과는 편백정유 흡입집단이 대조집단보다 2주차, 4주차로 기간이 경과 할수록 우울감이 감소함을 나타냈고, 편백정유 흡입집단이 대조집단보다 스트레스 정도는 감소하였으나, 통계적인 유의성은 나타나지 않았다. 본 연구에서 시간이 경과 할수록 우울감이 감소되었다는 결과는 향기요법으로써 편백정유의 장기적인 사용 효과를 나타냈다는 점에서 그 의의가 있다. The purpose of this study was to assess the effects of aromatherapy using Chamaecyparis obtusa essential oil. Twenty college students volunteers participated in this study. The volunteers were randomly allocated into two groups. Two groups were divided into Chamaecyparis obtusa essential oil group and denatured alcohol group. They exposed to the smell of incense oil for 4 weeks (28 days) of sleep during the light diffusion method naturally. As a result, the inhalation of Chamaecyparis obtusa essential oil group than the control group showed decreasing more depression of fourth week than second week. In this study, the depression was more decreased over time. It results has significance.

공동형 보염기를 갖는 모델 스크램제트 엔진의 흡입구 측면효과를 고려한 3차원 통합 유동해석

염효원(Hyo-Won Yeom),김성진(Sung-Jin Kim),성홍계(Hong-Gye Sung),강상훈(Sanghoon Kang),양수석(Soosuk Yang) 한국추진공학회 2009 한국추진공학회 학술대회논문집 Vol.2009 No.11

모델 스크램제트 엔진의 3차원 유동특성 이해를 위하여 다단의 충격파를 발생 시키는 흡입구부터(외부 유동영역) 공동형 보염기, 연소기, 노즐이 포함되는 엔빈 내부 전영역을 통합한 수치해석을 수행하였다. κ-ω SST 난류모델과 Sarkar모델이 적용된 저 레이놀즈 수 κ-ε 난류모델의 해석결과를 실험 결과와 비교하였으며, 흡입구의 측면효과(intake side wall effects)를 살펴보기 위하여 측면의 유무에 따른 유동특성을 관찰하였다. 본 연구에 소요되는 계산시간의 효율성을 위하여 계산영역을 다중블럭으로 구성하였으며, MPI(Massage Passing Interface) 병렬 계산 기법을 적용하였다. To identify the detailed 3D flow characteristics of a model scramjet engine, a unified 3D numerical analysis was performed. The numerical domain of concern includes the entire flow path of the model scramjet engine extending from the intake to the nozzle exhaust. Turbulent models(κ-ω SST and low Reynolds number κ-ε with Sarkar model) were applied with comparison of experiment result. Intake side wall"s effect on flow characteristics was analyzed in view points of flow quality at inlet duct and near the flame holder as well. The code is paralleled with multi-block feature using MPI(Massage Passing Interface) library to speed up the 3D calculation.

17세기 초 조선에서 유행한 ‘唐毒疫’에 대한 연구

조원준(Won Joon Chough),김용익(Young Ik Kim),염기복(Kee Bok Yeom),임효종(Hyo Jong Lim),정우열(Woo Yeal Jeong),전병훈(Byung Hun Jeon) 한의병리학회 2004 동의생리병리학회지 Vol.18 No.2