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- 저자 : 홍우람(W. Hong) (검색결과 4 건)
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다양한 출구조건이 적용된 초음속 흡입구 공력불안정성 수치적 연구
홍우람(W. Hong),최요한(Y. Choe),김종암(C. Kim) 한국전산유체공학회 2013 한국전산유체공학회 학술대회논문집 Vol.2013 No.5
The present study numerically investigates the flow instability around supersonic inlet, called inlet buzz. Though the flow conditions change linearly, behavior of inlet buzz alters hysteretically. In order to simulate the inlet buzz hysteretic character, computations are conducted with varying mass flow rate. The mass flow rate condition is controlled by an exit throttling plug which moves back and forth to change an exit area. In this paper, a set of simulations with mass flow rate control are presented. This simulations focus on hysteretic buzz characteristics of supersonic inlet according to mass flow rate and the historic path of the mass flow rate change. Firstly, an inlet buzz case with decreasing mass flow rate is simulated. In this process, the inlet buzz characteristic changes from the first mode of a low frequency regime to the second mode of a high frequency regime. In the next, the effect of the increasing mass flow rate on the inlet buzz is examined. This case shows another kind of the buzz transition that the buzz frequency becomes higher in the third mode. The hysteretic inlet buzz has many similarities to the fundamentals of a pipe-type musical instrument such as self-excited feed-back mechanism and overblowing. Considering the similarities, the hysteretic characteristics of an inlet buzz is discussed in the instrumental acoustic point of view.
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받음각이 있는 3차원 초음속 흡입구 주위의 유동진동 해석
김정민(J. Kim),홍우람(W. Hong),김종암(C. Kim) 한국전산유체공학회 2011 한국전산유체공학회 학술대회논문집 Vol.2011 No.5
A supersonic inlet at angle of attack has anti-symmetric pressure distribution, and it can make flow instability and structural problem. In this study, numerical analysis of three-dimensional inviscid flow was conducted under various throttle ratio and angle of attack conditions. Throttle ratio was defined as the ratio of the exit area to the smallest cross section area at inlet, and the ratio is controlled from 0 to 2.42. At various angle of attack, the characteristics of steady and unsteady flow around supersonic inlet is observed under different throttling ratios. From these results, pressure recovery curves and pressure history curves were plotted by post processing. Using pressure history data, FFT analysis is also carried out. Through these processes, it shows the tendency of pressure distribution anti-symmetricity and changing dominant frequency as increasing angle of attack.
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익형에서의 synthetic jet을 이용한 박리제어 mechanism
김상훈(S.H. Kim),김우레(W. Kim),홍우람(W. Hong),김종암(C. Kim) 한국전산유체공학회 2007 한국전산유체공학회 학술대회논문집 Vol.2007 No.-
Separation control has been performed using synthetic jets airfoil at high angle of attack. Computed results demonstrated that stall characteristics and control surface performance could be substantially improved by resizing separation vortices. It was observed that the actual flow control mechanism and flow structure is fundamentally different depending on the range of synthetic jet frequency. For low frequency range, small vortices due to synthetic jet penetrated to the large leading edge separation vortex, and as a result, the size of the leading edge vortex was remarkably reduced. For high frequency range, however, small vortex did not grow up enough to penetrate into the leading edge separation vortex. Instead, synthetic jet firmly attached the local flow and influenced the circulation of the virtual airfoil shape which is the combined shape of the main airfoil with the separation vortex. Theses results show the characteristic of unsteady flow of single synthetic jet. Beside, we researched on multi-array synthetic jet to obtain applicable synthetic jet velocity. Multi-location synthetic jet is proposed to eliminate small vortex on suction surface of airfoil. With the results, we concluded that the flow around airfoil is stable by high frequency synthetic jet with elimination of small vortex and confirmation of stable flow. Moreover, performance of multi-array/multi-location synthetic jet can be improved by changing phase angle of multi-location synthetic jet.
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HFCVD 증착 온도 변화에 따른 단결정 다이아몬드 표면 형상 및 성장률 변화
권진욱,김민수,장태환,배문기,김성우,김태규,Gwon, J.U.,Kim, M.S.,Jang, T.H.,Bae, M.K.,Kim, S.W.,Kim, T.G. 한국열처리공학회 2021 熱處理工學會誌 Vol.34 No.5
Following Silicon Carbide, single crystal diamond continues to attract attention as a next-generation semiconductor substrate material. In addition to excellent physical properties, large area and productivity are very important for semiconductor substrate materials. Research on the increase in area and productivity of single crystal diamonds has been carried out using various devices such as HPHT (High Pressure High Temperature) and MPECVD (Microwave Plasma Enhanced Chemical Vapor Deposition). We hit the limits of growth rate and internal defects. However, HFCVD (Hot Filament Chemical Vapor Deposition) can be replaced due to the previous problem. In this study, HFCVD confirmed the distance between the substrate and the filament, the accompanying growth rate, the surface shape, and the Raman shift of the substrate after vapor deposition according to the vapor deposition temperature change. As a result, it was confirmed that the difference in the growth rate of the single crystal substrate due to the change in the vapor deposition temperature was gained up to 5 times, and that as the vapor deposition temperature increased, a large amount of polycrystalline diamond tended to be generated on the surface.
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