Processing math: 100%
  • Title/Summary/Keyword: Incompressible fluids

Search Result 289, Processing Time 0.022 seconds

On Implementation of the Finite Difference Lattice Boltzmann Method with Internal Degree of Freedom to Edgetone

  • Kang, Ho-Keun;Kim, Eun-Ra
    • Journal of Mechanical Science and Technology
    • /
    • v.19 no.11
    • /
    • pp.2032-2039
    • /
    • 2005
  • The lattice Boltzman method (LBM) and the finite difference-based lattice Boltzmann method (FDLBM) are quite recent approaches for simulating fluid flow, which have been proven as valid and efficient tools in a variety of complex flow problems. They are considered attractive alternatives to conventional finite-difference schemes because they recover the Navier-Stokes equations and are computationally more stable, and easily parallelizable. However, most models of the LBM or FDLBM are for incompressible fluids because of the simplicity of the structure of the model. Although some models for compressible thermal fluids have been introduced, these models are for monatomic gases, and suffer from the instability in calculations. A lattice BGK model based on a finite difference scheme with an internal degree of freedom is employed and it is shown that a diatomic gas such as air is successfully simulated. In this research we present a 2-dimensional edge tone to predict the frequency characteristics of discrete oscillations of a jet-edge feedback cycle by the FDLBM in which any specific heat ratio γ can be chosen freely. The jet is chosen long enough in order to guarantee the parabolic velocity profile of a jet at the outlet, and the edge is of an angle of α=23o. At a stand-off distance w, the edge is inserted along the centerline of the jet, and a sinuous instability wave with real frequency is assumed to be created in the vicinity of the nozzle exit and to propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations resulting from periodic oscillation of the jet around the edge.

EFFECT OF WALL PROXIMITY ON DRAG AND LIFT FORCES ON A CIRCULAR CYLINDER (벽 근접 효과에 의한 물체의 항력 양력 변화)

  • Park, Hyun-Wook;Lee, Chang-Hoon;Choi, Jung-Il
    • Journal of computational fluids engineering
    • /
    • v.17 no.3
    • /
    • pp.68-74
    • /
    • 2012
  • Near-wall effect on wakes behind particles is one of the important factors in precise tracking of particles in turbulent flows. However, most aerodynamic force models for particles did not fully consider the wall effect. In the present study, we focused on changes of hydrodynamic forces acting on a particle depending on wall proximity. To this end, we developed an immersed boundary method with multi-direct forcing incorporated to a fully implicit decoupling procedure for incompressible flows. We validate the present immersed boundary method through two-dimensional simulations of flow over a circular cylinder. Comprehensive parametric studies on the effect of the wall proximity on the drag and lift forces acting on an immersed circular cylinder in a channel flow are performed in order to investigate general flow patterns behind the circular cylinder for a wide range of Reynolds number (0.01 Re 200). As the cylinder is closer to the wall, the drag coefficient decreases while the lift coefficient increases with a local maximum. Maximum drag and lift coefficients for different wall proximities decrease with increment of Reynolds number. Normalized drag and lift coefficients by their maximum values show universal correlations between the coefficients and wall proximity in a low Reynolds number regime (Re 1).

A STUDY ON A MULTI-LEVEL SUBSTRUCTURING METHOD FOR COMPUTATIONS OF FLUID FLOW (유동계산을 위한 다단계 부분 구조법에 대한 연구)

  • Kim J.W.
    • Journal of computational fluids engineering
    • /
    • v.10 no.2
    • /
    • pp.38-47
    • /
    • 2005
  • Substructuring methods are often used in finite element structural analyses. In this study a multi-level substructuring(MLSS) algorithm is developed and proposed as a possible candidate for finite element fluid solvers. The present algorithm consists of four stages such as a gathering, a condensing, a solving and a scattering stage. At each level, a predetermined number of elements are gathered and condensed to form an element of higher level. At the highest level, each sub-domain consists of only one super-element. Thus, the inversion process of a stiffness matrix associated with internal degrees of freedom of each sub-domain has been replaced by a sequential static condensation of gathered element matrices. The global algebraic system arising from the assembly of each sub-domain matrices is solved using a well-known iterative solver such as the conjugare gradient(CG) or the conjugate gradient squared(CGS) method. A time comparison with CG has been performed on a 2-D Poisson problem. With one domain the computing time by MLSS is comparable with that by CG up to about 260,000 d.o.f. For 263,169 d.o.f using 8 x 8 sub-domains, the time by MLSS is reduced to a value less than 30% of that by CG. The lid-driven cavity problem has been solved for Re = 3200 using the element interpolation degree(Deg.) up to cubic. in this case, preconditioning techniques usually accompanied by iterative solvers are not needed. Finite element formulation for the incompressible flow has been stabilized by a modified residual procedure proposed by Ilinca et al.[9].

A COMPUTATIONAL ANALYSIS FOR OUTLET SHAPE DESIGN TO SUPPRESS FLOW RECIRCULATION IN A ROTATING-DISK CVD REACTOR (회전원판형 CVD 장치의 유동 재순환을 억제하는 출구부 형상 설계를 위한 전산해석)

  • Park, J.J.;Kim, K.;Kwak, H.S.
    • Journal of computational fluids engineering
    • /
    • v.18 no.4
    • /
    • pp.74-81
    • /
    • 2013
  • A numerical design analysis is conducted to search for an optimal shape of outlet in a rotating-disk CVD reactor. The goal is to suppress flow recirculation that has been found in a reactor having a sudden expansion of flow passage outside of the rotating disk. In order to streamline gas flow, the sidewall at which the flow in the Ekman layer is impinged, is tilted. The axisymmetric laminar flow and heat transfer in the reactor are simulated using the incompressible ideal gas model. For the conventional vertical sidewall, the flow recirculation forming in the corner region could be expanded into the interior to distort the upstream flow. The numerical results show that this unfavorable phenomenon inducing back flow could be dramatically suppressed by tilting the sidewall at a certain range of angle. The assessment of deviation in deposition rate based on the characteristic isotherm illustrates that the sidewall tilting may expand the domain of stable plug-like flow regime toward higher pressure. A physical interpretation is attempted to explain the mechanism to suppress flow recirculation.

NUMERICAL SIMULATION OF TWO-DIMENSIONAL MICROORGANISM LOCOMOTION USING THE IMMERSED BOUNDARY METHOD (가상경계법을 적용한 2차원 미생물 이동에 관한 수치연구)

  • Maniyeri, Ranjith;Suh, Yong-Kweon;Kang, Sang-Mo
    • 한국전산유체공학회:학술대회논문집
    • /
    • 2009.11a
    • /
    • pp.164-169
    • /
    • 2009
  • Study on swimming of microorganisms like, sperm motility, cilia beating, bacterial flagellar propulsion has found immense significance in the field of biological fluiddynamics. Because of the complexity involved, it is challenging for the researchers to model such problems. Immersed boundary method has proved its efficacy in the field of biological fluiddynamics, The present work aims at performing a numerical study on the microorganism locomotion using the immersed boundary method proposed by Peskin[1]. A two-dimensional model of the microorganism is modeled as thin elastic filament described as a sine wave. The neutrally buoyant organism undergoing deformations is immersed in a viscous and incompressible fluid. The fluid quantities are described using Eulerian coordinates and the immersed body is represented by Lagrangian coordinates. The Eulerian and Lagrangian variables are connected by the Dirac delta function. The Navier-Stokes equations governing the fluid flow are solved using the fractional step method on a staggered Cartesian grid system. The developed numerical code in FORTRAN will be validated by comparing the numerical results with the available results.

  • PDF

Interactive Fluid Simulation Method for Mobile Device (모바일 기기를 위한 실시간 유체 시뮬레이션 엔진)

  • Kim, Do-Yub;Song, Oh-Young;Ko, Hyeong-Seok
    • 한국HCI학회:학술대회논문집
    • /
    • 2009.02a
    • /
    • pp.463-468
    • /
    • 2009
  • This paper proposes a method for extending simulating fluid on mobile device, which was only possible on desktop PC. Fluid simulation is done by solving Navier-Stokes equation numerically, and previous research were mainly focused on numerical stability [1], and realism [2]. However, such methods assume rich computational resources, which is not available on mobile devices. On the other hand, rigid-body solver is the mostly used physically-based technique [3], and only simple height field-based method is released for fluid simulation [4]. To overcome these problems, we proposes a modified incompressible fluid dynamics solver for the mobile device, and also we propose a technique for visualizing fluids on the mobile device.

  • PDF

A NUMERICAL STUDY ON THE FLOW CHARACTERISTICS OF GAS CHROMATOGRAPHIC COLUMN (가스 크로마토그래픽 컬럼의 유동특성에 대한 수치적 연구)

  • Kim T.-A.;Kim Youn J.
    • 한국전산유체공학회:학술대회논문집
    • /
    • 2005.10a
    • /
    • pp.21-26
    • /
    • 2005
  • Gas Chromatography (GC) is a wisely technique used for the separation and analysis of liquid and gas sample. Separation of the sample vapors is achieved via their differential migration through a capillary column with an insert carrier gas. The identity and quantity of each vapor in the mixer can be determined from its retention time in the column and a particular property of the gas, such as thermal conductivity, which can be related to the concentration of sample vapor in the carrier gas. Therefore, the flow characteristics in the spiral gas chromatographic column are numerically investigated in this study. Especially, different pressure drop between the front and the rear of GC column with various flow rates is estimated the governing equations are derived from making using of three-dimensional Naver-Stokes equation with incompressible and laminar model due to the nature of low Reynolds number flow. Using a commercial code, FLUENT, the pressure and flow fields in GC column are calculated with various flow rates. The characteristics of thermal cycling which is one of the most important factors affecting the column efficiency and analysis time is also estimated. Furthermore, numerical analyses are also carried out by using commercial code, ANSYS, with various values of power, which is applied to the heating element located at lower GC column.

  • PDF

Incompressible Turbulent Flow Simulation of the Rotor-Stator Configuration (비압축성 Navier Stokes 방정식을 이용한 2차원 터빈 익렬내의 난류유동해석)

  • Kim H. W.;Park W. G.;Jung Y. R.;Kim K. S.;Moon S.-G.
    • 한국전산유체공학회:학술대회논문집
    • /
    • 1995.10a
    • /
    • pp.225-234
    • /
    • 1995
  • 터빈익렬내부의 유동해석을 위해 비압축성 점성유동해석을 이용한 수치 해석 프로그램을 개발하였다. 지배방정식으로는 2차원의 비정상 비압축성 Navier-Stokes 방정식을 일반화된 곡선좌표계로 전환하여 암시적으로(implicitly) 반복적인 시간진행방법을 이용하여 유동해석을 하였다. 지배방정식의 각항들은 시간에 대해 1차의 정확도 그리고 영역에 대해서는 2차의 정확도, 대류항에 대해서는 3차의 정확도를 가지는 Upwind기법을 적용하였다. 특히, 실험적 접근이 매우 어려운 터빈의 정익과 회전하고 있는 동익과의 상호운동을 멀티블럭기법과 데이터 interface를 통해 보다 쉽게 해석할 수 있었다. 본 연구결과는 정익만을 계산한 타 연구자의 결과와의 비교시 매우 일치하였으며 물리적인 유동을 잘 파악할 수 있었다. 난류유동 해석을 위해서 Baldwin-Lomax 모델을 적용하였다.

  • PDF

SEPARATION CONTROL MECHANISM USING SYNTHETIC JET ON AIRFOIL (익형에서의 synthetic jet을 이용한 박리제어 mechanism)

  • Kim, S.H.;Kim, W.;Hong, W.;Kim, C.
    • 한국전산유체공학회:학술대회논문집
    • /
    • 2007.10a
    • /
    • pp.60-66
    • /
    • 2007
  • Separation control has been performed using synthetic jets on airfoil at high angle of attack. Computed results demonstrated that stall characteristics and control surface performance could be substantially improved by resizing separation vortices. It was observed that the actual flow control mechanism and flow structure is fundamentally different depending on the range of synthetic jet frequency. For low frequency range, small vortices due to synthetic jet penetrated to the large leading edge separation vortex, and as a result, the size of the leading edge vortex was remarkably reduced. For high frequency range, however, small vortex did not grow up enough to penetrate into the leading edge separation vortex. Instead, synthetic jet firmly attached the local flow and influenced the circulation of the virtual airfoil shape which is the combined shape of the main airfoil with the separation vortex. Theses results show the characteristic of unsteady flow of single synthetic jet. Beside, we researched on multi-array synthetic jet to obtain applicable synthetic jet velocity. Multi-location synthetic jet is proposed to eliminate small vortex on suction surface of airfoil. With the results, we concluded that the flow around airfoil is stable by high frequency synthetic jet with elimination of small vortex and confirmation of stable flow. Moreover, performance of multi-array/multi-location synthetic jet can be improved by changing phase angle of multi-location synthetic jet.

  • PDF

DETACHED EDDY SIMULATION OF BASE FLOW IN SUPERSONIC MAINSTREAM (초음속 유동장에서 기저 유동의 Detached Eddy Simulation)

  • Shin, J.R.;Won, S.H.;Choi, J.Y.
    • 한국전산유체공학회:학술대회논문집
    • /
    • 2008.03a
    • /
    • pp.104-110
    • /
    • 2008
  • Detached Eddy Simulation (DES) is applied to an axisymmetric base flow at supersonic mainstream. DES is a hybrid approach to modeling turbulence that combines the best features of the Reynolds-averaged Navier-Stokes RANS) and large-eddy simulation (LES) approaches. In the Reynolds-averaged mode, the model is currently based on either the Spalart-Allmaras (S-A) turbulence model. In the large eddy simulation mode, it is based on the Smagorinski subgrid scale model. Accurate predictions of the base flowfield and base pressure are successfully achieved by using the DES methodology with less computational cost than that of pure LES and monotone integrated large-eddy simulation (MILES) approaches. The DES accurately resolves the physics of unsteady turbulent motions, such as shear layer rollup, large-eddy motions in the downstream region, small-eddy motions inside the recirculating region. Comparison of the results shows that it is necessary to resolve approaching boundary layers and free shear-layer velocity profiles from the base edge correctly for the accurate prediction of base flows. The consideration of an empirical constant CDES for a compressible flow analysis may suggest that the optimal value of empirical constant CDES may be larger in the flows with strong compressibility than in incompressible flows.

  • PDF