• Title/Summary/Keyword: Viscous vortex

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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.

Comparison of Two Viscous Models for Vortex Methods (와법에 사용되는 2가지 점성모델의 비교)

  • Jung, Jae-Hoon;Yoon, Jin-Sup;Jin, Dong-Sik;Ahn, Cheol-O;Lee, Sang-Hwan
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.518-523
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    • 2001
  • Vortex methods were originally conceived as a tool to model the evolution of unsteady, incompressible, high Reynolds number flows of engineering interest. Recently various methods have been proposed for simulating the diffusion in vortex methods for two-dimensional incompressible flows. We test the diffusion schemes of vortex methods. In this paper we directly compare the particle strength exchange scheme with the vorticity redistribution scheme in tenus of their accuracy and computational efficiency. Comparisons between both viscous models described are presented for short-time runs of impulsively started flows past a circular cylinder for Reynolds number of 60. The particle strength exchange scheme has been shown more accurate and efficient than the vorticity redistribution scheme.

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A STUDY OF INCOMPRESSIBLE VISCOUS FLOW ANALYSIS BY VORTEX-IN-CELL METHOD (보오텍스 인 셀 방법을 이용한 점성유동해석 연구)

  • Lee, J.H.;Kim, Y.C.;Lee, K.J.;Suh, J.C.
    • 한국전산유체공학회:학술대회논문집
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    • 2011.05a
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    • pp.78-85
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    • 2011
  • The Vortex-In-Cell(VIC) method combined with panel method is applied to the analysis of incompressible unsteady viscous flow. The dynamics of resulting flow is governed by the vorticity transport equation in Lagrangian form with vortex particle representation of the flow field. A regular grid which is independent to the shape of a body is used for numerical evaluation based on immersed boundary technique. With an introduction of this approach, the development and validation of the VIC method is presented with some computational results for incompressible viscous flow around two or three dimensional bodies such as wing section, sphere, finite wing and marine propeller.

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Numerical Analysis on Hydrodynamic Forces Acting on Side-by-Side Arranged Two-Dimensional Floating Bodies in Viscous Flows (점성유동장에 병렬배치된 2차원 부유체에 작용하는 유체력에 관한 수치해석)

  • Heo, Jae-Kyung;Park, Jong-Chun
    • Journal of the Society of Naval Architects of Korea
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    • v.49 no.5
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    • pp.425-432
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    • 2012
  • Viscous flow fields of side-by-side arranged two-dimensional floating bodies are numerically simulated by a Navier-Stokes equation solver. Two identical bodies with a narrow gap are forced to heave and sway motions. Square and rounded bilge hull forms are compared to find out the effects of vortex shedding on damping force. Wave height, force RAOs, added mass and damping coefficients including non-diagonal cross coefficients are calculated and a similarity between the wave height and force RAOs is discussed. CFD which can take into account of viscous damping and vortex shedding shows better results than linear potential theory.

Numerical Analysis of Unsteady Viscous Flow Through a Weis-Fogh Type Ship Propulsion Mechanism Using the Advanced Vortex Method

  • Ro Ki-Deok;Kang Myeong-Hun;Kong Tae-Hee
    • Journal of Advanced Marine Engineering and Technology
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    • v.29 no.7
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    • pp.769-778
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    • 2005
  • The velocity and pressure fields of a ship's Weis-Fogh type propulsion mechanism are studied in this paper using an advanced vortex method. The wing (NACA0010 airfoil) and channel are approximated by source and vortex panels. and free vortices are introduced away from the body surfaces. The viscous diffusion of fluid is represented using the core-spreading model to the discrete vortices. The velocity is calculated on the basis of the generalized Biot-Savart law and the pressure field is calculated from an integral, based on the instantaneous velocity and vorticity distributions in the flow field. Two-dimensional unsteady viscous flow calculations of this propulsion mechanism are shown. and the calculated results agree qualitatively with the measured thrust and drag due to un-modeled large fluctuations in the measured data.

Simulation of Viscous Flow Past NACA 0012 Poil using a Vortex Particle Method (보오텍스 방법에 의한 순간 출발하는 2차원 날개 주위의 점성유동 모사)

  • Lee S. J.;Kim K. S.;Suh J. C.
    • 한국전산유체공학회:학술대회논문집
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    • 2004.03a
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    • pp.161-165
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    • 2004
  • In the vortex particle method based on the vorticity-velocity formulation for solving the Wavier-Stokes equations, the unsteady, incompressible, viscous laminar flow over a NACA 0012 foil is simulated. By applying an operator-splitting method, the 'convection' and 'diffusion' equations are solved sequentially at each time step. The convection equation is solved using the vortex particle method, and the diffusion equation using the particle strength exchange(PSE) scheme which is modified to avoid a spurious vorticity flux. The scheme is improved for variety body shape using one image layer scheme. For a validation of the present method, we illustrate the early development of the viscous flow about an impulsively started NACA 0012 foil for Reynolds number 550.

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Three-Dimensional Numerical Study on the Vortex Flow in a Horizontal Channels with High Viscous Fluid (수평채널 내 고 점성유체의 볼텍스 유동에 관한 3차원 수치해석(1))

  • Piao, Ri-Long;Kim, Jeong-Soo;Bae, Dae-Seok
    • Journal of Power System Engineering
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    • v.18 no.3
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    • pp.79-86
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    • 2014
  • Mixed convective vortex flow in the three-dimensional rectangular channel filled with high viscous fluid(Pr=909) is investigated computationally under various operating conditions. The Reynolds number is varied from 0 to $5{\times}10^{-1}$, the Rayleigh number from $10^3$ to $5{\times}10^4$. The three-dimensional governing equations are discretized using the finite volume method. The effects of Reynolds number and Rayleigh number are presented and discussed. From a parametric study, it is found that vortex flow pattern of mixed convection in rectangular channels can be classified into three flow patterns basically, but the new vortex flow structures containing wave rolls are found, which are affected by Rayleigh number and Reynolds number. From this results, we can draw a flow regime map to delineate various vortex flow patterns in the high viscosity fluid mixed convective flow.

Study of Energy Separation Mechanism in Vortex Tube by CFD (볼텍스 튜브의 에너지 분리 현상에 관한 수치해석 연구)

  • Choi, Won-Chul;Chung, Myung-Kyoon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.32 no.2
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    • pp.92-99
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    • 2008
  • The "energy separation phenomenon" through a vortex tube has been a long-standing mechanical engineering problem whose operational principle is not yet known. In order to find the operational principle of the vortex tube, CFD analysis of the flow field in the vortex tube has been carried out. It was found that the energy separation mechanism in the vortex tube consists of basically two major thermodynamic-fluid mechanical processes. One is the isentropic expansion process at the inlet nozzle, during which the gas temperature is nearly isentropically cooled. Second process is the viscous dissipation heating due to the high level of turbulence in both flow passages toward cold gas exit as well as the hot gas exit of the vortex tube. Since the amount of such a viscous heating is different between the two passages, the gas temperature at the cold exit is much lower than that at the hot exit.

An Investigation on the Formation Characteristics of a Single Vortex Interacting with Counterflow Nonpremixed Flame (대향류 비예혼합화염과 상호작용하는 단일 와동의 생성특성에 관한 연구)

  • Yoo, Byung-Hun;Oh, Chang-Bo;Hwang, Chul-Hong;Lee, Chang-Eon
    • 한국연소학회:학술대회논문집
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    • 2002.11a
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    • pp.49-56
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    • 2002
  • A two-dimensional direct numerical simulation is performed to investigate the formation characteristics of a single vortex interacting with $CH_4/N_2$-Air counterflow nonpremixed flame. The numerical method was based on a predictor-corrector scheme for a low Mach number flow. The detailed transport properties and a 16-step augmented reduced mechanism are adopted in this calculation. The budgets of the vorticity transport equation arc examined to reveal the mechanisms leading to the formation, evolution and dissipation of a single vortex interacting with counterflow nonpremixed flame. It is found that the stretching term, which depends on the azimuthal component of vorticity, and radial velocity, mainly generates vortieitv in non-reacting and reacting flows. The viscous and baroclinic torque term destroy the vorticity in non-reacting flow. In addition, the baroclinic torque term due to density and pressure gradient generates vorticity, while viscous and the volumetric expansion terms due to density gradient destroy vorticity in reacting flow.

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Analysis of Viscous Flow Around an Impulsively Started Marine Propeller Using VIC(Vortex In Cell) Method (VIC(Vortex In Cell) 방법을 이용한 순간 출발하는 프로펠러 주위의 점성유동 해석)

  • Lee, Jun-Hyeok;Kim, Yoo-Chul;Lee, Youn-Mo;Suh, Jung-Chun
    • Journal of the Society of Naval Architects of Korea
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    • v.49 no.1
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    • pp.26-32
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    • 2012
  • The 3-D unsteady viscous flow around an impulsively started rotating marine propeller is simulated using VIC(Vortex-In-Cell) method which is adequate to analyze the strong vortical flow around complicatedly-shaped body. The computational procedure is governed by the vorticity transport equation in Lagrangian form. In order to solve the equation, a regular grid which is independent to the shape of a body is introduced and each term of the equation is evaluated numerically on the grid by applying immersed boundary concept. In this paper, the overall algorithm including the formulation of governing equations and boundary conditions is described and some computational results are presented with discussing their physical validity.