선형 안정성 이론을 이용한 압축성 축 대칭 원뿔 경계층의 천이지점 예측

박동훈(Dong-Hoon Park),박승오(Seung-O Park) 한국항공우주학회 2008 韓國航空宇宙學會誌 Vol.36 No.5

본 연구에서는 축 대칭 원뿔 형상 위의 압축성 경계층의 천이 지점을 선형 안정성 이론 과 e<SUP>N</SUP>-method를 이용하여 예측하였다. 축 대칭 좌표계에서의 압축성 유동 지배 방정식으로부터 압축성 원뿔 경계층의 선형 안정성 방정식을 얻었으며 안정성 방정식을 2차 정확도의 유한 차분법을 이용하여 계산하는 수치 프로그램을 개발하였다. 개발 된 코드로 원뿔 경계층의 안정성 특성 및 2차원 교란의 증폭률을 계산하고 실험결과와의 비교를 통해 검증을 수행하였다. 얻어진 교란의 증폭률을 활용하여 e<SUP>N</SUP>-method를 통해 천이지점 예측을 수행하였다. 풍동 시험 및 비행 시험 결과와의 비교를 통해 비행 조건에 있는 마하수 4와 8사이의 원뿔 경계층에 대한 본 연구의 천이지점의 예측 능력을 확인하였다. 또한 벽면 냉각이 경계층 내부 교란의 안정성 및 천이 지점에 미치는 영향을 분석하였다. In this study, the transition Reynolds number of compressible axi-symmetric sharp cone boundary layer is predicted by using a linear stability theory and the e<SUP>N</SUP>-method. The compressible linear stability equation for sharp cone boundary layer was derived from the governing equations on the body-intrinsic axi-symmetric coordinate system. The numerical analysis code for the stability equation was developed based on a second-order accurate finite-difference method. Stability characteristics and amplification rate of two-dimensional second mode disturbance for the sharp cone boundary layer were calculated from the analysis code and the numerical code was validated by comparing the results with experimental data. Transition prediction was performed by application of the e<SUP>N</SUP>-method with N=10. From comparison with wind tunnel experiments and flight tests data, capability of the transition prediction of this study is confirmed for the sharp cone boundary layers which have an edge Mach number between 4 and 8. In addition, effect of wall cooling on the stability of disturbance in the boundary layer and transition position is investigated.

남한산성 소나무림의 19년간 (1993~2011년) 식생구조 변화와 관리방안

이경재 ( Kyong Jae Lee ),한봉호 ( Bong Ho Han ),이학기 ( Hak Gi Lee ),노태환 ( Tai Hwan Noh ) 한국환경생태학회 2012 한국환경생태학회지 Vol.26 No.4

본 연구는 2010년 세계문화유산 잠정목록에 등록된 국가사적 제57호 남한산성을 대상으로 과거 문헌자료와 현장조사를 통해 식생구조 변화를 밝히고 역사·문화적 가치가 높은 남한산성의 식생복원을 위한 관리방안을 수립하고자 실시하였다. 남한산성 식생의 비오톱 분석 결과 대상지 면적 2,611,823㎡중 참나무류림이 40.8%이었고, 천이 가능성이 높은 소나무림이 16.5%로 청량산 일원과 서문에서 북문 일원, 남문에서 청량산 사이의 산 능선에 분포하고 있었다. 천이 가능성이 낮은 소나무림은 4.7%로 남한산초등학교 뒤 산림에 주로 분포하고 있었고, 천이가 진행중인 소나무림은 2.9%, 도태중인 소나무림은 2.1%였다. 19년간 식생구조 변화 분석 결과 소나무림→소나무 및 참나무류 혼효림→참나 무류림→서어나무림으로 천이가 예측되었고, 시간이 경과함에 따라 참나무류의 세력이 확대되었다. 남한산성 소나무림의 식생 관리방안은 식생구조 특성을 고려하여 관리권역을 구분하였고, 관리권역은 소나무림 경관유지지역 553,508㎡, 소나무림 경관복원지역 114,293㎡, 적극적 관리지역 205,306㎡, 자연천이 유도지역 1,169,973㎡이었다. This study, targeting Namhan Mountain Fortress which was designated as a No. 57 national historic site and placed on the World Heritage Tentative List in 2010, was intended to identify the change of vegetation structures by reviewing past references, pictures, research data and additionally conducting a site survey. Also, it was designed to draw up measures for restoring vegetation suitable for historically and culturally valuable Namhan Mountain Fortress. According to the biotope mapping of study site, Quercus spp. forest distributed a greatest part of area with 40.8% of 2,611,823 . Pinus densiflora forest, highly likely to go through ecological succession, was dispersed in the whole region of Cheongryangsan, the area from West Gate to North Gate and the ranges between South Gate to Cheongryangsan with taking 16.5%. Pinus densiflora forest with a low probability of succession amounted to 4.7% and was dispersed mainly in the forest behind Namhansan elementary school. Pinus densiflora going on the ecological succession is distributed a portion of 2.9%. And the currently dying out Pinus densiflora forest amounted to 2.1%. As a result of analysis of the vegetation structure for 19 years, the succession from Pinus densiflora forest to Pinus densiflora and succession from Quercus spp. mixed forest to Quercus spp. forest to Carpinus laxiflora forest were predicted. Additionally, Quercus spp. expanded its dominance over time. According to the characteristics of each classified zone, the site was categorized into 553,508m² area of Pinus densiflora forest area for the landscape maintenance, 114,293 area of Pinus densiflora forest area for the landscape restoration, 205,306m² area of Pinus densiflora forest area for the disclimax, and 1,169,973m² area of Pinus densiflora forest area for inducing ecological succession.

e<SUP>N</SUP>–Method를 이용한 초음속 영역에서의 평판 및 원뿔형 경계층의 천이 예측

장제선(Je-Sun Jang),박승오(Seung-O Park) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-

This paper is about the code that realizes the e<SUP>N</SUP>-Method for boundary-layer transition prediction. The e<SUP>N</SUP>-Method based on the linear stability theory is applied to predicting boundary-layer transition frequently. This paper deals with the construction of code, stability analysis and the calculation of N-factor. The results of transition prediction using the e<SUP>N</SUP>-Method for flat plate/cone compressible boundary-layers are presented.

한국형발사체 75톤급 엔진 시동특성 해석

문윤완(Yoonwan Moon),박순영(Soon-Young Park),정은환(Eunhwan Jung) 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.5

발사체에 사용되는 액체로켓엔진을 개발할 때, 엔진의 작동성을 검증하기 위해서는 엔진 시동 과정을 결정하여야 한다. 엔진을 구성하는 각 구성품의 경우, 수류시험, 상사시험 등의 사전 시험을 통해 정상상태에서의 유동학적 특성을 파악하여 본 시험을 수행할 수 있다. 하지만 구성품의 조립체인 엔진의 경우, 구성품에서는 겪을 수 없는 천이조건에서 작동하여야 하므로 구성품의 시험 결과만으로는 엔진의 천이구간 특성을 예측하기는 매우 어렵다. 따라서 새롭게 설계된 엔진은 초기 시동 과정이 문제를 발생시키는 경우가 많다. 이러한 구성품과 엔진의 운영 조건에서의 간극을 최소화하기 위해 엔진의 천이구간을 파악할 수 있는 수학적 모델이 필요하며, 본 연구에서는 엔진시스템 측면에서 각 구성품을 모델링하여 개발하고 있는 한국형발사체 75톤급 액체로켓엔진의 초기 시동 시의 거동에 대해 예측하였다. When a liquid rocket engine is developed, a procedure of startup must be determined to validate the operability of LRE at first. In cases of LRE components the steady state flow characteristics of components can be understood by pre-test such as similarity test, hydraulic test etc. before main operation test. However, in case of a LRE as assembly of components, LRE must be experienced relative long transient state because inner pressure of temperature of LRE combustor should be operated from ≤1 bar, ≤298 K to high combustion pressure and temperature. Therefore it is very difficult to predict transient characteristics of LRE because the components have never been experienced during a component test. In order to minimize a gap of operation condition between LRE and components tests it is necessary to develop a mathematical model of LRE for understanding transient characteristics of LRE. From the viewpoint of LRE system, components and system were mathematically modeled, the strartup behavior of KSLV-II 75 tonf LRE, one of transient characteristics, were predicted.

다단계 모의 열화재의 재료강도 평가와 수명예측

권재도,진영준,장순식 대한기계학회 1993 대한기계학회논문집 Vol.17 No.9

In the case of life prediction on the structures and machines after long service, it is natural to consider a degradation problems. Most of degradation data form practical structures are isolated data obtained at the time of periodical inspection or repair. From such data, it may be difficult to obtain the degradation curve available and necessary for life prediction. In this paper, for the purpose of obtaining a degradation curves, developed the simulate degradation method and fatigue test and Charpy impact test were conducted on the degraded, simulate degraded and recovered materials. Fatigue life prediction were conducted by using the relationship between fracture transition temperature (DBTT : vTrs) obtained from the Charpy impact test through the degradation process and fatigue crack growth constants of m and C obtained from the fatigue test.

CFD에 의한 2D 에어포일 공력특성 및 3D 풍력터빈 성능예측

김범석(Bum-suk Kim),김만응(Mann-eung Kim),이영호(Young-ho Lee) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.7

Despite of the laminar-turbulent transition region co-exist with fully turbulence region around the leading edge of an airfoil, still lots of researchers apply to fully turbulence models to predict aerodynamic characteristics. It is well known that fully turbulent model such as standard k-model couldn't predict the complex stall and the separation behavior on an airfoil accurately, it usually leads to over prediction of the aerodynamic characteristics such as lift and drag forces. So, we apply correlation based transition model to predict aerodynamic performance of the NREL (National Renewable Energy Laboratory) Phase Ⅳ wind turbine. And also, compare the computed results from transition model with experimental measurement and fully turbulence results. Results are presented for a range of wind speed, for a NREL Phase Ⅳ wind turbine rotor. Low speed shaft torque, power, root bending moment, aerodynamic coefficients of 2D airfoil and several flow field figures results included in this study. As a result, the low speed shaft torque predicted by transitional turbulence model is very good agree with the experimental measurement in whole operating conditions but fully turbulent model(k- ε) over predict the shaft torque after 7m/s. Root bending moment is also good agreement between the prediction and experiments for most of the operating conditions, especially with the transition model.

1㎿급 수평축 조류발전용 터빈 블레이드 형상 기본설계 및 성능예측

김범석(Bum-suk Kim),음학진(Hark-jin Eum),김만응(Mann-eung Kim) 한국유체기계학회 2008 유체기계 연구개발 발표회 논문집 Vol.2008 No.-

난류모델 변화에 따른 수평축 풍력터빈 유동해석 및 출력성능 예측

김범석(Bum-suk Kim),음학진(Hark-jin Eum),원종범(Jong-bum Won),김만응(Mann-eung Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

Despite of the laminar-turbulent transition region co-exist with fully turbulence region around the leading edge of an airfoil, still lots of researchers apply to fully turbulence models to predict aerodynamic characteristics. It is well known that fully turbulent model such as standard k-model couldn't predict the complex stall and the separation behavior on an airfoil accurately, it usually leads to over prediction of the aerodynamic characteristics such as lift and drag forces. So, we apply correlation based transition model to predict aerodynamic performance of the NREL (National Renewable Energy Laboratory) Phase Ⅳ wind turbine. And also, compare the computed results from transition model with experimental measurement and fully turbulence results. Results are presented for a range of wind speed, for a NREL Phase Ⅳ wind turbine rotor. Low speed shaft torque, power, root bending moment, aerodynamic coefficients of 2D airfoil and several flow field figures results included in this study. As a result, the low speed shaft torque predicted by transitional turbulence model is very good agree with the experimental measurement in whole operating conditions but fully turbulent model(k-ε) over predict the shaft torque after 7m/s. Root bending moment is also good agreement between the prediction and experiments for most of the operating conditions, especially with the transition model.

익형 주위의 층류와 난류가 혼합된 유동해석

김철완(C.W. Kim),이융교(V.G. Lee) 한국전산유체공학회 2009 한국전산유체공학회 학술대회논문집 Vol.2009 No.4

In the present paper, transition turbulence model is applied to the NACA64(3)618. and detailed flow features are studied. The turbulence model is sensitive to the boundary layer grid quality and y+ oi the grid was limited to I. The prediction of the transition region is dependent on the local flow condition. The pressure coefficient distribution of the transition turbulence model is compared with that of the fully turbulent mode and the drag distribution of the transition turbulence model was compared with that of the wind tunnel test.

다양한 난류 모델에 따른 익형 특성 예측

김철완(C.W. Kim),이융교(Y.G. Lee),이장연(J.Y. Lee) 한국전산유체공학회 2007 한국전산유체공학회 학술대회논문집 Vol.2007 No.-

In the present paper, some difficulties encountered in predicting airfoil characteristics are described and solutions for those problems are discussed Since drag is determined by the amounts of pressure and, especially, shear stress, accurate estimation of shear stress is very crucial. However shear stress computation is dependent on the grid density and turbulence model, it should be consistent in preparing grid and turbulence model. When the transition from laminar to turbulent happens at the middle of airfoil, CFD solver should divide the region into laminar and turbulent region based on the transition location.