효율적인 냉각 방식 선정을 위한 탐색창 냉각 특성 해석 연구

김만식,이동민,Kim, Manshik,Lee, Dong Min 한국군사과학기술학회 2017 한국군사과학기술학회지 Vol.20 No.2

In this paper, cooling characteristics of seeker windows were examined using the Sinda-Fluint software. Various cooling methods were considered to satisfy the limit temperature of the cooled seeker window which would be exposed to excessive aerodynamic heating conditions by varying coolant type and mass flow rate of coolant. Due to the enhanced heat transfer between the coolant and the seeker window, internally cooled seeker window which uses liquid coolant showed lowered temperature distribution in the window compared to internally cooled seeker window which uses gas coolant. External film cooled seeker window also showed good cooling characteristics because it reduces the convective heat flux to the seeker window fundamentally. It was also confirmed that the temperature and the temperature gradient of seeker windows were significantly reduced for the cases which use external film cooling additionally to the gas and liquid cooled seeker window.

초음속 주유동 환경에서의 막냉각 특성 시험 연구

김만식(Manshik Kim),이동민(Dong Min Lee) 한국항공우주학회 2017 韓國航空宇宙學會誌 Vol.45 No.4

본 연구에서는 초음속 주유동 환경에서의 막냉각 특성에 대해 적외선 열상법을 적용한 시험을 수행하였다. 막냉각 시험은 수축형 막냉각 노즐을 갖는 쐐기형 막냉각 시편을 이용해 마하수 3.0, 단위 길이 당 레이놀즈수 42.53×10<SUP>6</SUP> 와 69.35×10<SUP>6</SUP> 인 조건을 구현한 자유-제트 시험 설비에서 수행하였다. 모사 탐색창에 해당하는 PEEK의 표면 온도를 계측하여 막냉각 효율을 산출하였고 받음각 및 분사율이 막냉각 효율에 미치는 영향을 분석하였다. 막냉각을 적용하지 않는 경우와 비교할 때, 막냉각을 적용할 경우 측정된 PEEK의 표면 온도가 크게 감소하였다. 막냉각의 유용성은 시간에 따른 PEEK의 표면 온도로부터 산출한 열유속 특성으로도 확인할 수 있다. 분사율이 증가할수록 보호되는 PEEK의 영역이 주유동과 막냉각 유동의 흐름 방향으로 확장되었다. In this paper, film cooling characteristics at supersonic free stream conditions were examined experimentally by applying an IR-thermography. Film cooling experiments were carried out in a free-jet facility at Mach number of 3.0 and with unit Reynolds number of 42.53×10<SUP>6</SUP> and 69.35×10<SUP>6</SUP> using wedge shaped film cooling model which has a converging film cooling nozzle. Film cooling efficiency was calculated by measuring the surface temperature of PEEK(Polyether Ether Ketone) and the effects of angle of attack and blowing ratios on the film cooling efficiency were examined. The measured wall temperature was significantly reduced by the film cooling flow compared with the results without the film cooling flow. The usefulness of film cooling was also confirmed by the surface heat flux calculated using the surface temperature history of PEEK. As the blowing ratio increases the protected area of PEEK was also expanded along the direction of free stream and film cooling flow.

DES와 FW-H 음향상사법을 이용한 탠덤 실린더의 공력소음 특성 연구

김만식(Manshik Kim),이윤규(Youn Kyu Lee) 한국항공우주학회 2018 韓國航空宇宙學會誌 Vol.46 No.11

본 연구에서는 항공기 랜딩 기어와 유사한 형태의 탠덤 실린더에 대해 DES (Detached Eddy Simulation)와 FW-H(Ffowcs Williams and Hawkings) 음향상사법을 이용한 전산공력 소음해석을 수행하였다. 실린더 중심 간 거리 3.7D 조건에 대한 전산공력소음해석 결과를 탠덤 실린더를 지나는 외부 유동 특성 및 원거리 소음을 계측한 선행 연구 결과와 비교하였다. 전방 실린더의 상/하부에서 발생한 와류(Vortex)가 특징적인 주파수를 갖고 후방실린더에 충돌하면서 소음 발생원이 되는 것을 확인하였다. DES와 FW-H 음향상사법을 이용한 전산공력소음해석 방법의 타당성을 확인한 후, 전방 실린더의 후방에 분할판을 적용한 경우의 전산공력소음해석을 수행하였다. 전방 실린더의 후방에 분할판이 적용되면 전방실린더의 상/하부에서 발생하는 와류의 특징을 변화시키고 이극자 소음원 크기를 감소시켜 특정 주파수 대역에서 발생하는 소유 크기가 감소하는 것을 확인하였다. In this paper, aerodynamic noise simulation was conducted using DES (Detached Eddy Simulation) and FW-H (Ffowcs Williams and Hawkings) acoustic analogy for the tandem cylinders which have configuration similar to a landing gear of airplanes. Numerical simulation for the tandem cylinders whose centers are 3.7D apart was carried out and results were compared with the measured data such as flow characteristics, pressure coefficients on the cylinder surfaces and far-field noise characteristics. It was confirmed that periodically shedded vortices released at the upstream cylinder and impinged on the downstream cylinder surface are major sources of aerodynamic noise. After verifying the computational method of using DES and FW-H acoustic analogy for predicting aerodynamic noise of tandem cylinders, additional simulation was conducted to examine the effect of attaching a splitter plate at the rear of the upstream cylinder. It was confirmed that the noise level in specific frequency band decreased significantly because the splitter plate changed the vortex shedding features and reduced dipole noise source.

가시화용 디젤노즐에서의 캐비테이션 유동 특성 및 3차원 해석 연구

김만식(Manshik Kim),장용석(Yongsuk Jang),민경덕(Kyoungdoug Min) 한국자동차공학회 2002 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2002 No.5_3

Experiment was conducted in transparent acrylic nozzle model which was scaled up by 10 times in order to study the behavior of cavitation flow inside the nozzle holes. High speed CCD camera was used to visualize the flow inside sac chamber and holes. Refractive index matching technique was also used to prevent distortion of images. Reynolds number and Cavitation number was simultaneously matched in the same range of the real injector by means of controlling the flow rates and pressures.<br/> The experimental results shows that the difference between cavitation layer and liquid layer causes very turbulent flow inside the nozzle hole. At hole entrance the cavitation film firms a thin layer and grows along hole perimeter maintaining its croissant shape with increasing cavitation number. Also, the relation between cavitation inside the hole and the spray cone angle of injected spray was clarified. Using the 3 dimensional computational code, the location of cavitation was investigated.

유전알고리즘을 이용한 대형 디젤 엔진 운전 조건 최적화

김만식(Manshik Kim),Mike P. Liechty,Rolf D. Reitz 한국자동차공학회 2005 한국 자동차공학회논문집 Vol.13 No.2

하이브리드 방법을 이용한 비행 중 비행체 음향하중 예측에 관한 연구

박서룡,김만식,김홍일,이수갑,Park, Seoryong,Kim, Manshik,Kim, Hongil,Lee, Soogab 한국음향학회 2018 韓國音響學會誌 Vol.37 No.4

This paper performed the prediction of the acoustic loads applied to the surface of the flight vehicle during flight. Acoustic loads during flight arise from the pressure fluctuations on the surface of body. The conventional method of predicting the acoustic loads in flight uses semi-empirical method derived from theoretical and experimental results. However, there is a limit in obtaining the flow characteristics and the boundary layer parameters of the flight vehicle which are used as the input values of the empirical equation through experiments. Therefore, in this paper, we use the hybrid method which combines the results of CFD (Computational Fluid Dynamics) with semi-empirical methods to predict the acoustic loads acting on flight vehicle during flight. For the flight vehicle with cone-cylinder-flare shape, acoustic loads were estimated for the subsonic, transonic, supersonic, and Max-q (Maximum dynamic pressure) condition flight. For the hybrid method, two kind of boundary layer edge estimation methods based on CFD results are compared and the acoustic loads prediction results were compared according to empirical equations presented by various researchers. 본 논문에서는 비행 중 비행체 표면에 작용하는 음향하중 예측을 수행하였다. 비행 중 음향하중은 비행체 표면의 압력 변동에 의해 발생한다. 기존의 비행 중 음향하중 예측방법은 반경험적 방법으로 이론과 실험 결과를 기반으로 도출한 경험식을 활용한다. 하지만 경험식의 입력 값으로 사용되는 비행체 주변 유동특성 및 경계층 파라미터를 매번 실험을 통해 얻는 것에는 한계가 있다. 따라서 본 논문에서는 전산유체해석(Computational Fluid Dynamics, CFD) 결과를 반경험적 방법과 혼합하는 하이브리드 방법을 이용하여 비행 중 비행체에 작용하는 음향하중을 예측하였다. Cone-cylinder-flare 형상 비행체에 대해 아음속, 천음속, 초음속, 최대동압도달(Maximum dynamic pressure, Max-q) 시점의 비행 환경에 대한 음향하중 예측을 수행하였다. 하이브리드 방법 적용 시 전산유체해석결과를 기반으로 한 경계층 끝단 영역 판단 방법에 대해 비교하였고 여러 연구자에 의해 제시된 경험식에 따른 음향하중 예측결과를 비교하였다.

LIEF법을 이용한 고온 고압 조건에서 충돌 디젤 분무의 특성에 관한 연구

김용래(Yongrae Kim),김만식(Manshik Kim),민경덕(Kyoungdoug Min) 한국자동차공학회 2003 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

Diesel sprays injected into a combustion chamber of a small sized HSDI engine impinge 0 a piston surface. As a consequence, their vaporization, mixture formation and combustion process are affected by impingement phenomena. The liquid and vapor phase of diesel sprays impinging on a flat and hot wall were visualized under high temperature and pressure conditio by LIEF technique. The experiments were carried in a constant volume chamber and the injection pressure and impinging distance were varied to analyze the effect on impinging sprays.<br/> It was found that the radius and height of a impinging spray were almost constant regardless of the injection pressure. And the vapor distribution of a impinging spray injected at hig pressure was more uniform than low injection pressure.<br/>

광학 창 기밀구조 설계를 위한 그라파이트 개스킷의 압축/회복 특성 연구

채병찬(Byoungchan Chae),김만식(Manshik Kim) 한국항공우주학회 2019 한국항공우주학회 학술발표회 논문집 Vol.2019 No.11

산소 센서 감지도 및 열 손실 측면의 배기 매니폴드 및 CCC 시스템 유동 개선 연구

김한상(Han-Sang Kim),김만식(Manshik Kim),최명식(Myung-Sik Choi),민경덕(Kyoungdoug Min) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11

To meet future stringent emission legislation limits while making a good balance between engine power and emission standards in the development of new engine, an advanced exhaust system with close-coupled catalysts (CCC) must be developed. In this respect, it is essential to use computational fluid dynamics (CFD) in the design stage of exhaust system. To this end, CFD investigations of the exhaust flow characteristics for two types of exhaust manifold and CCC systems (Type 1 and Type 2) were performed in this study. The exhaust flow characteristics were compared and discussed in terms of three main factors such as O₂ sensing sensitivity, catalyst flow uniformity, and heat loss characteristics. Results indicate that Type 2 shows better flow uniformity and smaller heat loss than Type 1. Through this study, we can provide a basic insight into the useful guidance to design the exhaust system with improved flow-uniformity and catalyst light-off behavior.

그라파이트 개스킷의 압축/회복 특성에 따른 광학 창 기밀구조의 압축응력 거동

채병찬(Byoungchan Chae),김만식(Manshik Kim) 한국항공우주학회 2022 한국항공우주학회 학술발표회 논문집 Vol.2022 No.11