• Title/Summary/Keyword: Vortex viscosity

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The Effects of Surface Shear Viscosity and Surface Tension on a Columnar Vortex Interacting with a Free Surface (자유표면과 반응하는 수직와류에 대한 표면점성계수와 표면장력의 영향)

  • Kim Kyung-Hoon;Sohn Kwon;Kim Seok-Woo
    • Journal of the Korean Society of Visualization
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    • v.3 no.1
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    • pp.51-57
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    • 2005
  • Vertices terminating at free surface have been investigated extensively. Most of investigations, however, are focused on surface parallel vortices and little has been known about surface normal vortex or columnar vortex. Visualized experimental results utilizing LIF technique are discussed fur the purpose of characterization of columnar vortex interacting with a clean and a contaminated free surfaces and a solid body interface in the present investigation. The results reveal that surface tension changes due to surface contamination although bulk viscosity remains constant and eventually the behavior of a columnar vortex interacting with a contaminated free surface and a solid body interface are totally different from the clean free surface case.

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STABILITY ANALYSIS OF REGULARIZED VISCOUS VORTEX SHEETS

  • Sohn, Sung-Ik
    • Bulletin of the Korean Mathematical Society
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    • v.53 no.3
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    • pp.843-852
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    • 2016
  • A vortex sheet is susceptible to the Kelvin-Helmhotz instability, which leads to a singularity at finite time. The vortex blob model provided a regularization for the motion of vortex sheets in an inviscid fluid. In this paper, we consider the blob model for viscous vortex sheets and present a linear stability analysis for regularized sheets. We show that the diffusing viscous vortex sheet is unstable to small perturbations, regardless of the regularization, but the viscous sheet in the sharp limit becomes stable, when the regularization is applied. Both the regularization parameter and viscosity damp the growth rate of the sharp viscous vortex sheet for large wavenumbers, but the regularization parameter gives more significant effects than viscosity.

Development and Decay of Columnar Vortex in Two Phases Interface; Gas/Liquid, Solid/Liquid (기/액, 고/액 2상 경계면에서의 수직와류의 성장과 소멸)

  • Kim, K.H.;Yang, S.Y.;Park, M.H.
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.241-246
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    • 2001
  • Vortices terminating at free surface have been investigated extensively. Most of investigations, however, are focused on surface parallel vortices and little has been known about surface normal vortex or columnar vortex. Visualized experimental results utilizing LIF technique are discussed for the purpose of characterization of columnar vortex interacting with a clean and a contaminated free surfaces and a solid body interface in the present investigation. The results reveal that surface tension changes due to surface contamination although bulk viscosity remains constant and eventually the behavior of a columnar vortex interacting with a contaminated free surface and a solid body interface are totally different from the clean free surface case.

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Experiments on Columnar Vortex with Free Surface using LIF (Laser Induced Fluorescence) Technique (유동가시화를 통한 자유표면과 와류 수직반응에 대한 실험적 연구)

  • Kim, S.W.;Kim, K.H.;Lee, S.H.
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.734-739
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    • 2000
  • Vortices terminating at free surface have been investigated extensively. Most of investigations, however, are focused on surface parallel vortices and little has been known about surface normal vortex or columnar vortex. Visualized experimental results utilizing LIF technique are discussed for the purpose of characterization of columnar vortex interacting with a clean and a contaminated free surfaces in the present investigation. The results reveal that surface tension changes due to surface contamination although bulk viscosity remains constant and eventually the behavior of a columnar vortex interacting with a contaminated free surface is totally different from the clean free surface case.

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Development and Decay of Columnar Vortex in two faces interface ; gas/liquid and solid/liquid

  • Lee, Seung-Hwan;Kim, Kyung-Hoon;Kim, Seok-Woo
    • Journal of ILASS-Korea
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    • v.6 no.2
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    • pp.29-36
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    • 2001
  • Vortices terminating at free surface have been investigated extensively. however. are focused on surface parallel vortices and little has been known about surface normal vortex or columnar vortex. Visualized experimental results utilizing LlF technique are discussed for the purpose of characterization of columnar vortex interacting with a clean and a contaminated free surfaces and a solid body interface in the present investigation. The results reveal that surface tension changes due to surface contamination although bulk viscosity remains constant and eventually the behavior of a columnar vortex interacting with a contaminated free surface and a solid body interface are totally different from the clean free surface case.

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Predicted Air Flow Around Objects Using the Discrete Vortex Method

  • Kim, Tae-Hyeung
    • Journal of Korean Society for Atmospheric Environment
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    • v.9 no.E
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    • pp.347-357
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    • 1993
  • The Lagrangian grid-free numerical method, the discrete vortex method, was applied to solve the Navier-Stokes euqations. This method avoids the introduction of numerical viscosity swamping the real physical viscosity at high Reynolds number, unlike Eulerian method, e.g. finite difference and element methods. The boundary integral equation method for the potential flow solution was included to make the discrete vortex method more feasible for complex geometries. The fast adaptive multipole expansion method was incorporated to reduce the computational time from $O(N^2)$ to O(N) for the computations of vortex-vortex interactions. The test problems were air flow around one circular cylinder and two circular cylinders in tandem with various gaps. The numerical results were in excellent gareement with the experimental and other computational results. The applicabilty of the method was discussed with the indoor and the outdoor air pollution problems, especially the contaminant transport in the recirculation regions.

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Effects of Vortex Viscosity Variation on the Flowfields in a Micro-slot between Rotating Surfaces of Revolution (와점성 변화가 회전곡면으로 이루어진 마이크로 슬롯 유동장에 미치는 영향)

  • Choi, G.W.;Kim, Youn-J.
    • Proceedings of the KSME Conference
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    • 2001.11b
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    • pp.591-596
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    • 2001
  • Micron-size mechanical devices are becoming more prevalent, both in commercial applications and in scientific inquiry. Within the last decade, a dramatic increase in research activities has taken place, mostly due to the rapidly expanding growth of applications in areas of MEMS(Micro-Electro-Mechanical Systems), bioengineering, chemical systems, and advanced energy systems. In this study, we have described the effects of vortex viscosity variation on the flowfields in a micro-slot between rotating surfaces of revolution using a micropolar fluid theory. In order to solve this problem, we have used boundary layer equations and applied non-zero values of the microrotation vector on the wall. The results are compared with the corresponding flow problems for Newtonian fluid. Results show that the coefficient $\delta$ controls the main part of velocity ${\upsilon}_x$ and the coefficient M controls the main part of microrotation component ${\Omega}_{\theta}$.

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Vortex behavior in the inertial flow of viscoelastic fluids past a confined cylinder

  • Kim, Ju Min;Kim, Chongyoup;Chung, Changkwon;Ahn, Kyung Hyun;Lee, Seung Jong
    • Korea-Australia Rheology Journal
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    • v.16 no.3
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    • pp.117-128
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    • 2004
  • The effect of molecular parameters on the steady vortex behaviors in the inertial viscoelastic flow past a cylinder has been investigated. FENE-CR model was considered as a constitutive equation. A recently developed iterative solution method (Kim et al., (in press)) was found to be successfully applicable to the computation of inertial viscoelastic flows. The high-resolution computations were carried out to understand the detailed flow behaviors based on the efficient iterative solution method armed with ILU(0) type pre-conditioner and BiCGSTAB method. The discrete elastic viscous split stress-G/streamline upwind Petrov Galerkin (DEVSS-G/SUPG) formulation was adopted as a stabilization method. The vortex size decreased as elasticity increases. However, the vortex enhancement was also observed in the case of large extensibility, which means that the vortex behavior is strongly dependent upon the material parameters. The longitudinal gradient of normal stress was found to retard the formation of vortex, whereas the extensional viscosity played a role in the vortex enhancement. The present results are expected to be helpful for understanding the inertial vortex dynamics of viscoelastic fluids in the flow past a confined cylinder.

Numerical study on the oblique shock wave/vortex interaction (경사충격파와 와류 상호작용에 대한 수치적 연구)

  • Mun, Seong-Mok;Kim, Jong-Am;No, O-Hyeon
    • 한국항공운항학회:학술대회논문집
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    • 2004.11a
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    • pp.240-246
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    • 2004
  • For the prediction on the onset of oblique shock wave-induced vortex breakdown, computational studies on the Oblique Shock wave/Vortex Interaction (OSVI) are conducted and compared with both experimental results and analytic model. A Shock-stable numerical scheme, the Roe scheme with Mach number-based function (RoeM), and a two-equation eddy viscosity-transport approach are used for three-dimensional turbulent flow computations. The computational configuration is identical to available experiment, and we attempt to ascertain the effect of parameters such as a vertex strength, streamwise velocity deficit, and shock strength at a freestream Mach number of 2.49. Numerical simulations using the ${\kappa}-{\omega}SST$ turbulence model and suitably modeled vortex profiles are able to accurately reproduce many fine features through a direct comparison with experimental observations. The present computational approach to determine the criterion on the onset of oblique shock wave-induced vortex breakdown is found to be in good agreement with both the experimental result and the analytic prediction.

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Evaluation of URANS Turbulence Models through the Prediction of the Flow around a Circular Cylinder (원형 실린더 주위의 유동해석을 통한 URANS 난류 모델 성능 비교)

  • Kim, Minjae;Shin, Jihwan;Kwon, Laeun;Lee, Kurnchul
    • Journal of the Korea Institute of Military Science and Technology
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    • v.17 no.6
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    • pp.861-867
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    • 2014
  • In the present study, the flow around a circular cylinder at $Re=3.6{\time}10^6$ is numerically simulated using URANS approach. The objective of this study is to evaluate the turbulence models(Realizable k-${\varepsilon}$, RNG k-${\varepsilon}$) through the prediction of the unsteady flow characteristics around the cylinder. The time-averaged drag coefficients and vortex shedding phenomenon in the wake region are compared to available experimental data and other numerical results. The simulation with Realizable k-${\varepsilon}$ model is found to be more dissipative due to large eddy viscosity predicted in the wake region while the simulation with RNG k-${\varepsilon}$ model predicts a complex vortex shedding phenomenon with more coherent structures realistically.