http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
임채민(Chae-Min LIM),권용훈(Yong-Hun KWEON),?木俊之(Toshiyuki AOKI),김희동(Heuy-Dong KIM) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
The effects of nozzle-lip thickness on the relationship between screech tone and broadband shock-associated noise were experimentally investigated using a convergent-divergent nozzle with a design Mach number of 2.0. Overall sound pressure levels (OASPL) and noise spectra were obtained at far-field locations. Schlieren optical system was used to visualize the flow-fields of supersonic jets. A baffle plate was installed at the exit of the nozzle and its size was varied to obtain different nozzle-lip thicknesses. Experiment was carried out over a wide range of nozzle pressure ratios from 2.0 and 18.0, which corresponds to over- and underexpanded conditions. The results obtained clearly show that the screech tones are influenced by the nozzle-lip thickness. It is found that the screech tone and its peak amplitude are strongly dependent on whether the jet is over-expanded and under-expanded at the nozzle exit.
임채민(Chae-Min Lim),Young-Ki Lee,김희동(Heuy-Dong Kim),Ryszard Szwaba 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
The plume-induced shock wave is a complex phenomenon, consisting of plume-induced boundary layer separation,<br/> separated shear layer, multiple shock waves, and their interactions. The knowledge base of plume interference effect on<br/> powered missiles and flight vehicles is not yet adequate to get an overall insight of the flow physics. Computational<br/> studies are performed to better understand the flow physics of the plume-induced shock and separation particularly at high<br/> plume to exit pressure ratio. Test model configurations are a simplified missile model and two rounded and porous<br/> afterbodies to simulate moderately and highly underexpanded exhaust plumes at the transonic/supersonic speeds. The<br/> result shows that the rounded afterbody and porous wall attached at the missile base can alleviate the plume-induced<br/> shock wave phenomenon, and improve the control of the missile body.
압력진동을 저감하기 위한 sub-cavity를 가진 초음속 공동유동에 대한 실험 및 수치해석적 연구
임채민(Chae-Min Lim),이영기(Young-Ki Lee),김희동(Heuy-Dong Kim) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
The effectiveness of passive control techniques for alleviating the pressure oscillation generated in a supersonic cavity flow was investigated numerically and experimentally, respectively. The control device includes a sub-cavity installed near the leading edge of a rectangular cavity. Time-dependent supersonic cavity flow characteristics with turbulent features were examined by using the three-dimensional, mass-averaged Navier-Stokes computation based on a finite volume scheme and large eddy simulation. The results show that the pressure oscillation near the trailing edge dominates overall time-dependent cavity pressure variations. Such an oscillation can be attenuated more significantly in the presence of the sub-cavity compared with the cavity without sub-cavity, and a larger sub-cavity leads to better control performance.
Counterflow 개념을 이용한 추력벡터 제어에 관한 실험적 및 수치해석적 연구
임채민(Chae-Min Lim),이권희(Kwon-Hee Lee),김희동(Heuy-Dong Kim) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
Experimental and computational studies were performed to investigate the effectiveness of a thrust vectoring method using a counterflow concept. A shadowgraph method was used to visualize the supersonic jet expanded from a two-dimensional convergent-divergent nozzle and deflected by a flow suction. The primary nozzle pressure and suction nozzle pressure ratios are varied between 3.0 and 5.0, and between 0.2 and 1.0 respectively. The present experimental and computational results showed that, for a given primary nozzle pressure ratio, a decrease in the suction nozzle pressure ratio produced an increased thrust vector angle, and during the change processes of the suction pressure, a hysteresis effect of the thrust vectoring was found through the wall pressure distributions.
Discrete Inlet Slits를 가지는 Spiral 제트유동에 관한 연구
임채민(Chae-Min Lim),이호준(Ho-June Lee),이권희(Kwon-Hee Lee),김희동(Heuy-Dong Kim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Although spiral jet technology is widely being applied in a variety of industrial fields, detailed flow mechanism inside the spiral nozzle is not well understood yet. According to the previous works, the spiral flow components are generated by non-uniform inlet velocity distributions or pressure disturbances at the annular inlet of a convergent nozzle. However, this fact has never been clarified by experiment or computational method. In the present study, the three-dimensional Naver-Stokes equations are solved using a fully implicit finite volume method. The effect of discrete inlet slits on the spiral jet flow is investigated and validated with previous experimental data available. The results obtained show that, at any position near discrete inlets, two vortices with a co-axial and tangential velocity components of the opposite direction were generated and, near the nozzle exit, changed to a vortex with those of one direction.