• Title/Summary/Keyword: vortex core

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Numerical Analysis on the Flow Field and Heat Transfer Characteristics of Longitudinal Vortices in Turbulent Boundary Layer - On the Common Flow Down - (3차원 난류경계층 내에 존재하는 종방향 와동의 유동장 및 열전달 특성에 관한 수치해석(I) - Common Flow Down에 관하여 -)

  • Yang Jang-Sik
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.9
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    • pp.789-798
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    • 2005

  • This paper is a numerical study concerning how the interactions between a pair of the vortices effect flow field and heat transfer. The flow field (common flow down) behind a vortex generator is modeled by the information that is available from studies on a half-delta winglet. Also, the energy equation and the Reynolds-averaged Wavier-Stokes equation for three-dimensional turbulent flows, together with a two-layer turbulence model to resolve the near-wall flow, are solved by the method of AF-ADI. The present results predict that the boundary layer is thinned in the regions where the secondary flow is directed toward the wall and thickened where it Is directed away from the wall. Although some discrepancies are observed near the center of the vortex core, the overall performance of the computational model is found to be satisfactory.

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Behavior of the Vortex Flux in a Polycrystalline $Y_1Ba_2Cu_3O_{7-\delta}$Superconductor in a Rotational Experiment (회전실험에서의 다결성 $Y_1Ba_2Cu_3O_{7-\delta}$ 초전도체내의 vorterx flux의 거동)

  • 박성재;김용석;김채옥
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.11 no.9
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    • pp.752-757
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    • 1998

  • Rotational Magnetization-vector measurements have been performed on a polycrystalline $Y_1Ba_2Cu_3O_{7-\delta}$ sample in field-cooled condition at 4.2 K. The experimental results show that vortex flux density(B) consists of 3 groups :(1) a weak pinning part ($B_w$) which stays at a fixed angle relative to the magnetic field f(H) ; (2) a strong pining part($B_s$) which rotates rigidly with the sample and has same magnitude with the sample rotation, and(3) and intermediated pining part ($B_i$) which rotates rigidly with the sample, but whose magnitude changes with the sample rotation Our results have been explained in terms of a distribution in the strength of the vortex pinning torque and a repulsive intervortex torque.

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Simulations of the Unsteady Viscous Flow Around an Impulsively Started Cylinder Using Improved Vortex Particle Method (개선된 입자와법을 이용한 급 출발하는 실린더 주위의 비정상 점성 유동 시뮬레이션)

  • Jin, Dong-Sik;Lee, Sang-Hwan;Lee, Ju-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.5
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    • pp.733-743
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    • 2000

  • We solve the integral representation of the Navier-Stokes equations in a lagrangian view by tracking the particles, which have vortex strengths. We simulate the unsteady viscous flow around an impulsively started cylinder using the vortex particle method. Particles are advanced via the Biot-Savart law for a lagrangian evolution of particles. The particle strength is modified based on the scheme of particle strength exchange. The solid boundary satisfies the no-slip boundary condition by the vorticity generation algorithm. We newly modify the diffusion scheme and the boundary condition for simulating an unsteady flow efficiently. To save the computation time, we propose the mixed scheme of particle strength exchange and core expansion. We also use a lot of panels to ignore the curvature of the cylinder, and not to solve the evaluation of the surface density. Results are compared to those from other theoretical and experimental works.

  • https://doi.org/10.22634/KSME-B.2000.24.5.733 인용 PDF

Study on the Angular Momentum of Axisymmetric Tropical Cyclone in the Developing Stage (발달 단계의 축대칭 열대저기압의 각운동량에 관한 연구)

  • Kang, Hyun-Gyu;Cheong, Hyeong-Bin
    • Atmosphere
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    • v.23 no.1
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    • pp.1-11
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    • 2013

  • The angular momentum transport of an idealized axisymmetric vortex in the developing stage was investigated using the Weather Research and Forecast (WRF) model. The balanced axisymmetric vortex was constructed based on an empirical function for tangential wind, and the temperature, geopotential, and surface pressure were obtained from the balanced equation. The numerical simulation was carried out for 6 days on the f-plane with the Sea Surface Temperature (SST) set as constant. The weak vortex at initial time was intensified with time, and reached the strength of tropical cyclone in a couple of days. The Absolute Angular Momentum (AAM) was transported along with the secondary circulation of the vortex. Total AAM integrated over a cylinder of radius of 2000 km decreased with simulation time, but total kinetic energy increased rapidly. From the budget analysis, it was found that the surface friction is mainly responsible for the decrease of total AAM. Also, contribution of the surface friction to the AAM loss was about 90% while that of horizontal advection was as small as 8%. The trajectory of neutral numerical tracers following the secondary circulation was presented for the Lagrangian viewpoint of the transports of absolute angular momentum. From the analysis using the trajectory of tracers it was found that the air parcel was under the influence of the surface friction continuously until it leaves the boundary layer near the core. Then the air parcel with reduced amount of angular momentum compared to its original amount was transported from boundary layer to upper level of the vortex and contributed to form the anti-cyclone. These results suggest that the tropical cyclone loses angular momentum as it develops, which is due to the dissipation of angular momentum by the surface friction.

  • https://doi.org/10.14191/Atmos.2013.23.1.001 인용 PDF KSCI