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장원근,권형일,조영민,최성임 한국항공우주학회 2011 한국항공우주학회 학술발표회 논문집 Vol.2011 No.11
The realization of supersonic jet should come from affordable economic costs and minimized environmental impacts. To achieve this goal, a shape of supersonic jet is optimized to minimize drag of aircraft and the ground sonic boom loudness. A design optimization framework is set up so that the requirements were satisfied by choosing the optimal combination of the shape design variables. In this research, surface definition of the supersonic jet is constructed using automatic surface generation program, which uses parametric relations through CAD interface. Aerodynamic performance analysis is performed by using 3-D panel method. The ground boom signature and noise loudness levels are calculated by predicting nonlinear propagation of the near-field pressure to the ground. Hybrid Genetic Algorithm selects an optimal configuration which minimizes drag and ground boom loudness level. This automatic preliminary design framework allows researchers to easily test for various shapes and selects an optimal design configuration.
스크램제트 공동 화염 보염기 형상에 따른 유동 특성의 수치적 연구
장원근,이학진,최성임,이덕주 한국항공우주학회 2014 한국항공우주학회 학술발표회 논문집 Vol.2014 No.4
차세대 제트 추진기관으로 주목받고 있는 스크램제트 엔진의 핵심은 연소기 내부에서의 성공적인 초음속 연소를 필요로 한다. 초음속 연소는 공기-연료 혼합(fuel-air mixing)의 정도에 따라 연소효율이 영향을 받게 된다. 공동형 화염 보염기(cavity flameholder)는 재순환 영역(recirculation zone)을 생성하여 연료 혼합의 효율을 높여 지속적인 초음속 연소가 진행될 수 있는 시간을 제공한다. 본 연구에서는 EDISON 전산유체역학 소프트웨어를 이용하여 공동형 화염 보염기를 지나는 초음속 유동의 재순환 영역의 유동 특성에 대한 전산 해석을 수행하였다. 초기 형상을 생성하여 유동 해석을 수행한 후, 3개의 형상 변수에 대한 매개 변수 연구를 통하여 공동의 형상과 위치에 따른 재순환영역의 제어가 가능함을 확인하였다. Scramjet is a promising air-breathing engine for future hypersonic cruise vehicles. With the scramjet, supersonic fuel-air mixing and combustion must be maintained within the combustor. To enhance the combustion, a recessed-type cavity flameholder, which is known to create recirculation zone, reduce ignition delay time and also provide a continuous source of auto-ignition, is often used. In this work, the flow characteristics of supersonic recirculation flow were numerically investigated by using EDISON-CFD Software. A parametric study is performed from baseline configuration with three shape parameters. In conclusion, the recirculation zone can be controlled by changing cavity shape and location.
장원근,신함옹,이동길,박영식,신성선,박종락,이기호,김인선 한국광학회 2014 Current Optics and Photonics Vol.18 No.5
We demonstrate a low-cost, superbly efficient way of etching for the nano-, and micro-sized pyramid patterns on (100)-oriented Si wafer surfaces for use as a patterned master. We show a way of producing functional optical films for the viewing angle direction brightness-enhancement of Lambertian LED (light emitting diode)/OLED (organic light emitting diode) planar lighting applications. An optimally formulated KOH (Potassium hydroxide) wet etching process enabled random-positioned, and random size-distributed (within a certain size range) pyramid patterns to be developed over the entire (100) silicon wafer substrates up to 8” and a simple replication process of master patterns onto the PC (poly-carbonate) and PMMA (polymethyl methacrylate) films were performed. Haze ratio values were measured for several film samples exhibiting excellent values over 90% suitable for LED/OLED lighting purposes. Brightness was also improved by 13~14% toward the viewing angle direction. Computational simulations using LightTools™ were also carried out and turned out to be in strong agreement with experimental data. Finally, we could check the feasibility of fabricating low-cost, large area, high performance optical films for commercialization.