• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
• /
• pp.363-366
• /
• 2011

마하 2의 초음속 풍동 장치에서 벤트 혼합기를 사용하여 혼합 연소실험을 수행하였다. 혼합실험에서는 헬륨을 사용하였고, 연소실험에서는 수소와 플라즈마 토치를 사용하여 연소 특성을 연구하였다. 혼합실험에서는 벤트 혼합기에 의해 수직분사임에도 불구하고 후류 혼합층에 많은 연료가 잔존하였다. 연소 실험의 경우 낮은 온도의 초음속 유동에서 플라즈마 토치를 사용한 점화와 연소되지 않은 연료-공기 혼합물의 충격파 유도 연소가 후류 영역에서 발생하였다. 열질식이 일어난 경우, shock train이 발생하며 이는 연소기내 연소 불안정성을 유도한다.

• 대한기계학회논문집
• /
• 제6권4호
• /
• pp.390-396
• /
• 1982

The onset of longitudinal vortices in horizontal Blasius flow isothermally heated from below is studied analytically. The assumption that at the onset of thermal instability the thermal disturbances are confined within the thermal boundary layer is employed for the limiting case of large Prandtl number. Polynomial representations for the basic quantities obtained by the integral method of the boundary layer analysis have been used. Then the system of differential equations and boundary conditions for disturbance quantities is reformulated in a convenient form so that the solutions may be constructed as rapidly convergent power series. The critical buoyancy parameter G $r_{x}$ $^{*}$ /R $e^{*1.5}$ falls between 2 and 6, which is about one order of magnitude lower than the existing experimental values. It is also shown that the positions of the onset of instability can be closely predicted by the present theory.y.y.

• 대한기계학회논문집
• /
• 제8권1호
• /
• pp.10-17
• /
• 1984

The critical conditions marking the onset of thermally induced vortices over an inclined iso-thermal plate are investigated using the linear stability theory. The stability equations are simplified by estimating the orders of magnitude of respective terms. The analysis is carried out under the assumption that for the system of large Prandtl numbers temperature disturbances are initiated within the conventional thermal boundary layer of the basic flow. The stability criteria obtained from the present results agree well with those of the existing quasi-parallel flow models. In addition it is found that the critical conditions generate the heat transfer correlation in good agreement with experiments. Therefore, it is suggested that the validity of existing theoretical models will be reexamined.

• 한국해양공학회지
• /
• 제8권1호
• /
• pp.16-22
• /
• 1994

수중 예인시스템의 동적 거동 해석을 위한 3차원 비선형 수학모델이 제시되었다. 수중 예인체는 세장보로 이상화되었으며, 보요소의 굽임강성 및 비틈강성의 영향이 수학모델에 포함되었다. 축류가 지배적인 비정상 상대유동장내의 세장예인체의 횡방향 운동에 따른 유체동역학적 반력과 기진력에 관한 비선형 3차원 수학 정식화가 수행되었다.

• 한국전산유체공학회지
• /
• 제5권3호
• /
• pp.40-46
• /
• 2000

Natural convection in a wide-gap horizontal annulus is considered, and the transition of flows from steady to oscillatory convection is investigated for the fluid with Pr=0.1. The unsteady streamfunction-vorticity equation is solved with finite difference method. As Rayleigh number is increased, the steady crescent-shaped flow bifurcates to a time-periodic flow with like-rotating eddies. And afterwards, a transition to an oscillatory multicellular flow with a counter-rotating eddy on the top of the annulus occurs. A transition from steady to an oscillatory flow occurs, but dual solutions and hysteresis phenomena are not observed.

• 대한기계학회논문집B
• /
• 제27권4호
• /
• pp.440-446
• /
• 2003

Steady-state structure and acoustic pressure responses of GH$_2$-LOx diffusion flames in stagnation-point flow configuration have been studied numerically with a detailed chemistry to investigate the acoustic instabilities. The Rayleigh criterion is adopted to judge the instability of the GH$_2$-LOx flames from amplification and attenuation responses at various acoustic pressure oscillation conditions for near-equilibrium to near-extinction regimes. Steady state flame structure showed that the chain branching zone is embedded in surrounding two recombination zones. The acoustic responses of GH$_2$-LOx flame showed that the responses in near-extinction regime always have amplification effect regardless of realistic acoustic frequency. That is, GH$_2$-LOx flame near-extinction is much sensitive to pressure perturbation because of the strong effect of a finite-chemistry.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2002년도 추계학술대회논문초록집
• /
• pp.390.1-390
• /
• 2002

In this study, we investigate the plugging effect on the CE type steam generator tube. The natural frequency and mode shape will be changed due to decrease of the effective mass distribution along the tube. We compared the variation of stability ratio for plugged tube with that fur unplugged one. The natural frequency increased because of removing the cooling water inside the steam generator tube, but the stability ratio decreased inversely because of changing the vibrational mode shape. We also investigated the turbulent excitation effect.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2000년도 춘계학술대회논문집
• /
• pp.492-498
• /
• 2000

As the disk rotation speed increases in information storage devices, aerodynamically excited disk vibration is induced by airflow around the disk. This paper investigates theoretical and experimental studies on the disk flutter instability in CD-ROM drives. The effect of airflow on the disk vibration is modeled as the distributed damping and lift forces. By analyzing the eigenvalue problem of the aero-elastic coupling model, we introduces a novel technique to predict the flutter speed by comparing experimental natural frequencies with analytical ones of a disk rotating in vacuum. The new method predicts that the vibration mode with two nodal diameters in a CD disk experiences the first flutter instability at 12,000 rpm.

• 설비공학논문집
• /
• 제2권4호
• /
• pp.268-278
• /
• 1990

Hydrodynamic stability equations are formulated for natural convection flows adjacent to a heated or cooled, inclined, isothermal surface in pure water at $4^{\circ}C$, where the density variation with temperature becomes nonlinear. The resulting stability equations, when reduced to ordinary differential equations by a similarity transformation, constitute a two-point boundary-value problem, which was solved numerically. It is found from the obtained stability results that the neutral stability curves are systematically shifted to have lower critical Grashof numbers, as the inclination angle of upward-facing plate increases. Also, the nose of the neutral stability curve becomes blunter as the angle increases. It implies that the greater the inclination of the upward-facing plate, the more susceptible of the flow to instability for the wide range of disturbance wave number and frequency.

• 대한설비공학회지:설비저널
• /
• 제17권4호
• /
• pp.489-498
• /
• 1988

An analysis has been given for the effect of viscous dissipation on the thermal instability of plane Couette flow between two parallel plates maintained at different constant temperatures. Under the assumption that the principle of the exchange of stabilities holds, stationary disturbance quantities in the form of longitudinal vortices are considered. The magnitudes of disturbance quantities are then represented as fast convergent power series so that the eigenvalue problem for determining the onset conditions of the thermal instability may be reduced to a simplified problem of finding the roots of a $4{\times}4$ determinant. It is shown that as the magnitude of the visucous dissipation increases the flow becomes more susceptible to instabilities, which is in very good agreement with previous results obtained in some related researches.