• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.864-870
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• 2001

Flame propagation along vortex tube was experimentally investigated. The vortex tube was generated by the ejection of propane from a nozzle through a single stroke motion of a speaker and the ignition was induced from a single pulse laser. Non-reactive flow fields were visualized using shadow technique. From these images, vortex ring size and translational velocity were measured in order to determine the ignition time and position. Flame structure and flame speed were measured using high speed CCD camera. Flame speed was accelerated during the initial stage of flame kernel growth, and reached near constant value during steady propagation period. Near the completion of propagation, flame speed was decelerated and then extinguished. Flame speed along the non-premixed vortex tube was found to be linearly proportional to circulation, which was similar to that of the flame propagation along premixed vortex ring. Ignition position minimally affects the propagation characteristics. These imply that flame is propagating along the maximum speed locus expected to be along stoichiometric contour and also support the existence of tribrachial flames.

• 기술사
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• 제31권5호
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• pp.32-35
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• 1998

• Wind and Structures
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• 제15권4호
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• pp.331-343
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• 2012

Thunderstorm downbursts are responsible for numerous structural failures around the world. The wind characteristics in thunderstorm downbursts containing vortex rings differ with those in 'traditional' boundary layer winds (BLW). This paper initially performs an unsteady-state simulation of the flow structure in a downburst (modelled as a impinging jet with its diameter being $D_{jet}$) using a computational fluid dynamics (CFD) method, and then analyses the pressure distribution on a solar updraft tower (SUT) in the downburst. The pressure field shows agreement with other previous studies. An additional pair of low-pressure region and high-pressure region is observed due to a second vortex ring, besides a foregoing pair caused by a primary vortex ring. The evolutions of pressure coefficients at five orientations of two representative heights of the SUT in the downburst with time are investigated. Results show that pressure distribution changes over a wide range when the vortices are close to the SUT. Furthermore, the fluctuations of external static pressure distribution for the SUT case 1 (i.e., radial distance from a location to jet center x=$D_{jet}$) with height are more intense due to the down striking of the vortex flow compared to those for the SUT case 2 (x=$2D_{jet}$). The static wind loads at heights z/H higher than 0.3 will be negligible when the vortex ring is far away from the SUT. The inverted wind load cases will occur when vortex is passing through the SUT except on the side faces. This can induce complex dynamic response of the SUT.

• 한국항공우주학회지
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• 제40권9호
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• pp.745-751
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• 2012

하이브리드 로켓은 축 방향의 산화제 유동과 고체 연료의 기화로 인한 벽면 분출 유동사이의 상호 간섭에 의해 복잡한 형태의 혼합 전단층이 존재한다. 연소실 입구에 링이 설치되어 있고 질량분사가 있는 실린더 유동에 대하여 압축성 효과를 고려한 LES(Large Eddy Simulation) 기법을 적용하여 수치계산을 수행하였다. 최근의 실험에 의하면 연료 중간에 링과 같은 다이아프램이 설치된 경우, 연소율의 증가가 관찰되었다. 계산 결과에 따르면, 축방향 유동과 벽면 분출 유동이 상호 간섭하여 발생하는 벽면 와류가 국부적인 연료 표면으로의 열전달을 증가시켜 실험에서 관찰되는 딤플이 생성되는 것을 확인하였다. 또한 연소실 입구에 설치된 링에 의하여 발생되는 와류는 벽면 와류가 보다 활발하게 생성되고 열전달과 혼합을 향상시키는 역할을 하며 이 때문에 연소율이 증가되는 것으로 보인다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1494-1498
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• 2007

Impulsive shooting noise is basically complex phenomenon which contains the linear and non-linear characteristics. For those reasons, numerical analysis of impulsive shooting noise has the difficulties in control of the numerical stability and accuracy on the simulation. In this research, Wave-number Extended Finite Volume Scheme (WEFVS) is applied to the numerical analysis of impulsive shooting noise. In the muzzle blast flow simulation, the generation of the precursor wave and the induced vortex ring are observed. Consequently, blast wave. vortex ring interaction and vortex ring. bow shock wave interaction are evaluated on the shooting process using the accurate and stable scheme. The sound generation in the interactions can be explained by the vorticity transport theorem. The shear layer is evolved behind the projectiles due to the jet flow. In these computations, the impulsive shooting noise is generated by the complex interaction with shooting process and is propagated to the far-field boundary. The impulsive shooting noise generation can be observed by the applications of WEFVS and analyzed by the physical phenomena.

• International Journal of Fluid Machinery and Systems
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• 제4권1호
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• pp.57-66
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• 2011

Radial-vaned air separators show a strong stall suppression effect in an axial flow fans. From a survey of existing literature on the effects and the author's data, a possible mechanism for the significant effects has been proposed here. The stall suppression is suggested to have been achieved by a combination of the following several effects; (1) suction of blade and casing boundary layers and elimination of embryos of stall, (2) separation and straightening of reversed swirling flow from the main flow, (3) induction of the fan main flow toward the casing wall and enhancement of the outward inclination of meridional streamlines across the rotor blade row, thus keeping the Euler head increase in the decrease in fan flow rate, and (4) reinforcement of axi-symmetric structure of the main flow. These phenomena have been induced and enhanced by a stable vortex-ring encasing the blade tips and the air separator. These integrated effects appear to have caused the great stall suppression effect that would have been impossible by other types of stall prevention devices. Thus the author would like to name the device "tip-vortex-ring assisted stall suppression device".

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 춘계 학술대회논문집
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• pp.35-40
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• 2002

The dynamic behaviors of the single vortex in a reacting and non-reacting methane-air jet flow were investigated numerically. The numerical method was based on a predictor-corrector for low Mach number flow A two-step global reaction mechanism was adopted as a combustion model. After fuel and air were developed entirely in computational domain, the single vortex was generated by an axisymmetric jet that was impulsed to emit a cold fuel. Through comparisons of single vortex in reacting and non-reacting jet flow, it was found that global dynamic behaviors and the mechanisms leading to the formation, transport processes of vortex ring were influenced significantly by heat release from reaction. In addition, the interaction between a single vortex and flame bulge generated by buoyance effect in a reacting jet flow was found.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 12th Asian Congress of Fluid Mechanics
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• pp.55.4-55.4
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• 2008

• 한국해양공학회지
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• 제36권2호
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• pp.108-114
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• 2022

Most studies on the shape of the steady vortex ring have been based on the Stokes stream function approach. In this study, the velocity approach is introduced as a trial approach. A contour dynamics method for fluid velocity is used to analyze the Norbury-Fraenkel family of vortex rings. Analytic integration is performed over the logarithmic-singular segment. A system of nonlinear equations for the discretized shape of the vortex core is formulated using the material boundary condition of the core. An additional condition for the velocities of the vortical and impulse centers is introduced to complete the system of equations. Numerical solutions are successfully obtained for the system of nonlinear equations using the iterative scheme. Specifically, the evaluation of the kinetic energy in terms of line integrals is examined closely. The results of the proposed method are compared with those of the stream function approaches. The results show good agreement, and thereby, confirm the validity of the proposed method.

• 대한기계학회논문집B
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• 제29권10호
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• pp.1101-1110
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• 2005

In this paper we present the numerical results of the behavior of the horizontal vortex generated by ejecting a liquid vertically upward from an orifice into the bulk fluid above the orifice. The numerical calculation has been performed for the axi-symmetric Navier-Stokes equation. A simple flow-visualization experiment was also conducted to qualitatively verify the numerical solutions. Three cases of the flow configurations studied in this paper are; firstly, the vortex was generated without any background rotation, secondly, the vortex was made under a full background rotation, and thirdly, the vortex was made during the spin-up process such that only the region adjacent to the side wall was set into motion viewed in the inertial frame of reference. It was shown that the swirl flow at the inlet boundary affects considerably the formation and development of the vortex for the second case. In the third case, it was remarkable to see that the vortex cannot penetrate into the region near to the side wall of the tank, because of the strong swirl flow and corresponding high pressure gradient in the region.