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안쪽축이 회전하는 환형관내 헬리컬 유동장의 실험적 연구
황영규,김영주,Hwang, Young-Kyu,Kim, Young-Ju 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.6
This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure drops and skin-friction coefficients have been measured for the fully developed flow of water and that of glycerine-water solution (44%) at a inner cylinder rotational speed of $0{\sim}600$ rpm, respectively. The transitional flow has been examined by the measurement of pressure drops and the visualization of flow field, to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients and to understand the flow instability mechanism. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure drops and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime. Consequently, the critical (axial-flow) Reynolds number decreases as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the excitation of taylor vortices.
황영규,허중식,최욱진,Hwang, Young-Kyu,Heo, Joong-Sik,Choi, Wook-Jin 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.6
Numerical and experimental investigations are performed for the molecular transition and slip flows in pumping channels of a disk-type drag pump. The flow occurring in the pumping channel develops from the molecular transition to the slip flow traveling downstream. Two different numerical methods are used in this analysis: the first one is a continuum approach in solving the Navier-Stokes equations with slip boundary conditions, and the second one is a stochastic approach through the use of the direct simulation Monte Carlo method. In the experimental study, the inlet pressures are measured for various outlet pressures in the range of 0.1{\sim}4Torr. From the present study, the numerical results of predicting the performance, obtained by both methods, agree well with the experimental data for the range of Knudsen number $Kn{\leq}0.1$ (i.e., the slip flow regime). But the results from the second method only agree with the experimental data for Kn>0.1(i.e., the molecular transition regime)
황영규,이윤용,이광원,Hwang, Young-Kyu,Lee, Yun-Yong,Lee, Kwang-Won 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.4
The hydrodynamic instability of the three-dimensional boundary-layer over a rotating disk has been numerically investigated for these flows; Ro = -1, -0.5, and 0, using linear stability theory. Detailed numerical values of the disturbance wave number. wave frequency. azimuth angle. radius (Reynolds number, Re) and other characteristics have been calculated for the pre-swirl flows. On the basis of Ekman and Karman boundary layer theory, the instability of the pre-swirl flows have been investigated for the unstable criteria. The disturbance will be relatively fast amplified at small fe and within wide bands of wave number compared with previously known Karman boundary-layer results. The flow (Ro =-0.5) is found to be always stable for a disturbance whose dimensionless wave number is greater than 0.9. It has a larger range of unstable interval than Karman boundary layer and can be unstable at smaller Re.
3단 원판형 드래그펌프의 배기 성능에 관한 실험적 연구
황영규(Young-Kyu Hwang),허중식(Joong-Sik Heo),권명근(Myoung-Keun Kwon),양성민(Seong-Min Yang) 한국유체기계학회 2001 유체기계 연구개발 발표회 논문집 Vol.- No.-
In this paper, the pumping performance of the three-stage disk-type drag pump which works in the outlet pressure range from 4 to 0.01 Torr is studied experimentally. The rotational speed of the pump is 24,000rpm, and nitrogen is used as a test gas. The pumping characteristics of various drag pumps are investigated. The inlet pressures are measured for various outlet pressures of the test pump. The maximum compression ratios for zero throughput are measured for three-stage, two-stage BSC type, helical-type, one-stage BSC type and one-stage OSC type, respectively.
황영규(Young-Kyu Hwang),허중식(Joong-Sik Heo) 한국유체기계학회 2000 유체기계 연구개발 발표회 논문집 Vol.- No.-
The direct simulation Monte Carlo (DSMC) method is applied to investigate the flow field of a disk-type drag pump. The pumping channels are cut on both sides of a rotating disk. The rotor has 10 Archimedes' spiral blades. In the present DSMC method, the variable hard sphere model is used as a molecular model, and the no time counter method is employed as a collision sampling technique. For simulation of diatomic gas flows, the Larsen-Borgnakke phenomenological model is adopted to redistribute the translational and internal energies.