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이복직(Bok Jik Lee) 한국전산유체공학회 2006 한국전산유체공학회지 Vol.11 No.3
Accurate prediction of a supersonic missile base drag continues to defy even well-rounded CFD codes. In an effort to address the accuracy and predictability of the base drags, the influence of grid system and competitive turbulence models on the base drag is analyzed. Characteristics of some turbulence models is reviewed through incompressible turbulent flow over a flat plate, and performance for the base drag prediction of several turbulence models such as Baldwin-Loman(B-L), Spalart-Allmaras(S-A), k-ε; k-ω model is assessed. When compressibility correction is injected into the S-A model, prediction accuracy of the base drag is enhanced. The NSWC wind tunnel test data are utilized for comparison of CFD and semi-empirical codes on the accuracy of base drag predictability: they are about equal, but CFD tends to perform better. It is also found that, as angle of attack of a missile with control fins increases, even the best CFD analysis tool we have lacks the accuracy needed for the base drag prediction.
Self-Ignition of Hydrogen in a Pipe by Rupture of Pressure Boundaries
Bok Jik Lee(이복직),Hyoung Jin Lee(이형진),In-Seuck Jeung(정인석) 한국연소학회 2009 KOSCOSYMPOSIUM논문집 Vol.- No.39
Direct numerical simulations with detailed reaction kinetics are conducted to investigate the mechanism of spontaneous ignition of hydrogen within a certain length of downstream pipe released by the failure of pressure boundaries of various geometric assumption to see their effect on the formation of flammable mixture volumes and the development of ignition sources. Numerical simulations are conducted using the unsteady, compressible two-dimensional axisymmetric Navier-Stokes equations for a chemically reactive multi-species mixture of ideal gases. And total number of cells is used about 4 millions. Only local ignition is developed in limited area such as boundary layer and the mixing of hydrogen and air is weak at the planar pressure boundary conditions, whereas the flame fronts at the contact region of hydrogen and air are developed at the pressure boundaries of the spherical shape. It is found that the initial formation of multi-dimensional shock wave and sufficient length of downstream pipe which allows the sufficient time of mixing by shock interactions are necessary for the spontaneous ignition kernel that is developed within the pipe length.
극초음속 충격파 풍동 설계/구축 및 성능시험 Part Ⅰ: 극초음속 충격파 풍동 설계 방법
이복직(Bok-Jik Lee),이형진(Hyoung-Jin Lee),김세환(Sei-Hwan Kim),정인석(In-Seuck Jeung) 한국항공우주학회 2008 韓國航空宇宙學會誌 Vol.36 No.4
극초음속으로 비행하는 추진기관이 직면하는 고속 유동 등 제반 현상을 모사하기 위한 지상시험 설비로 충격파 풍동을 설계, 구축한 후 성능 시험을 수행하였다. 개발된 준 일차원 작동 해석를 이용하여 설계점을 파악한 후, 극초음속 시험설비 구축을 위한 개념 설계를 완료하였다. 이어 단위 해석 코드를 이용하여 구체적인 성능 설계 및 각 구성품에 대한 설계를 완료, 구축한 후, 다양한 운용조건에서 성능시험을 수행하였다. 본 논문에서는 이론해석 결과를 바탕으로 이루어진 개념 설계와 준 1차원 다화학종 해석 코드를 이용한 개념설계 검증 및 성능설계 결과 등 극초음속 충격파 풍동 설계방법을 제시하였다. The shock tunnel as a hypersonic ground test facility was designed, constructed and its performance test was conducted to reproduce the high speed flow which the hypersonic propulsion system is encountered. The design points were understood and the conceptual design was completed using the quasi one dimensional operation analysis code. After that, the specific performance and compartment design were completed using CFD simulation as the part analysis. The facility was then constructed according to those design results and the performance test was conducted for various operation conditions. In this paper, we suggested the design method of hypersonic shock tunnel including the conceptual and performance design using theoretical analysis and the quasi ID Multi-species computational fluid dynamics code.
움직이는 격자계를 이용한 유도탄의 비정상 분리 유동해석
강경태,이복직,안창수,Kang, Kyoung-Tai,Lee, Bok-Jik,Ahn, Chang-Soo 한국군사과학기술학회 2007 한국군사과학기술학회지 Vol.10 No.2
Missile staging and airframe separation simulation were performed by using a numerical technique for simulating the dynamics of multiple moving bodies. A 6DOF model is fully integrated into the CFD solution procedure to determine the body dynamics. Chimera grid technique offered efficient CFD simulation of multiple moving bodies. Through this simulation the safety of deployed staging and airframe separation mechanism was verified.