11. Velocity-vorticity formulation for 3D natural convection in an inclined enclosure by BEMJure Ravnik, Leopold Škerget, Zoran Žunič, 2008, izvirni znanstveni članek Opis: A natural convection phenomenon is studied in cubic and parallelepipedal inclined enclosures. The simulation of coupled laminar viscous flow and heat transfer is performed using a novel algorithm based on a combination of singledomain Boundary element method (BEM) and subdomain BEM. The algorithm solves the velocity-vorticity formulation of the incompressible Navier-Stokes equations coupled with the energy equation using the Boussinesq approximation.The subdomain BEM is used to solve the kinematics equation, the vorticity transport equation and the energy equation. The boundary vorticity values, which are needed as boundary conditions for the vorticity transport equation, are calculated by singe domain BEM solution of the kinematics equation. Simulation results are compared with benchmark results for a cubic inclined enclosure for Rayleigh number values ▫$10^3Ključne besede: podobmočna metoda robnih elementov, hitrostno-vrtinčna formulacija, laminarni tok viskozne tekočine, naravna konvekcija, nagnjena kotanja, fluid mechanics, subdomain boundary element method, velocity-vorticity formulation, laminar viscous fluid flow, natural convection, inclined enclosure Objavljeno: 31.05.2012; Ogledov: 1468; Prenosov: 55 Povezava na celotno besedilo |
12. Boundary element method for thermal flows using k-[epsilon] turbulence modelsMatjaž Ramšak, Leopold Škerget, 2008, objavljeni znanstveni prispevek na konferenci Opis: Purpose - This paper aims to develop a multidomain boundary element method (BEM) for modeling 2D complex turbulent thermal flow using low Reynolds two-equation turbulence models. Design/methodology/approach - The integral boundary domain equations are discretised using mixed boundary elements and a multidomain method also known as a subdomain technique. The resulting system matrix is an overdetermined, sparse block banded and solved using a fast iterative linear least squares solver. Findings - The simulation of a turbulent flow over a backward step is in excellent agreement with the finite volume method using the same turbulent model. A grid consisting of over 100,000 elements could be solved in the order of a few minutes using a 3.0 GhzP4 and 1 GB memory indicating good efficiency. Originality/value - The paper shows, for the first time, that the BEM is applicable to thermal flows using k-▫$epsilon$▫. Ključne besede: thermal flow, heat exchange, turbulence, boundary element method, simulation Objavljeno: 31.05.2012; Ogledov: 802; Prenosov: 20 Povezava na celotno besedilo |
13. Magnetic particle separation in viscous flows by BEMMatjaž Hriberšek, Jure Ravnik, Primož Kocutar, 2011, objavljeni znanstveni prispevek na konferenci Opis: A boundary element method based solver for particle motion simulation in dilute suspensions under the influence of hydrodynamic and magnetic forces was applied. The Euler-Lagrangian formulation for simulation of dilute two-phase flow was applied. The algorithm solves the incompressible Navier-Stokes equations written in velocity-vorticity formulation. The non uniform magnetic field was defined analytically for the case of a set of long thin wires. The particle trajectories were computed by applying the 4th order Runge-Kutta method. The computed test case consisted of a narrow channel under the influence of a nonuniform magnetic field, where magnetite and aluminium particles were suspended in water. The results of computations show the distributions of particles along the channel and confirms the suitability of the proposed configuration as a separation device under ideal conditions. Ključne besede: boundary element method, laminar flow, magnetic particles, viscous fluids Objavljeno: 01.06.2012; Ogledov: 1656; Prenosov: 25 Povezava na celotno besedilo |
14. Simulation of unsteady fluid flow and heat transfer by BEMJure Ravnik, Leopold Škerget, 2011, objavljeni znanstveni prispevek na konferenci Opis: A boundary element method based solver for simulation of unsteady laminar viscous flow and heat transfer in three-dimensions has been developed. The algorithm solves the incompressible Navier- Stokes equations written in velocity-vorticity form and coupled with energy equation. Buoyancy is modelled within the Boussinesq approximation. The solver has recently been adapted for simulation of unsteady phenomena. The governing set of equations consists of the kinematics equation and transport equations for vorticity and temperature. Velocity and temperature boundary conditions are known, vorticity boundary conditions are calculated during the simulation by single domain BEM applied on the kinematics equation. The transport equations are solved by a domaindecomposition BEM approach, which yields sparse integral matrices and enables simulation using large computational grids. Rayleigh-Benard convection is used for a test case. In this case fluid is heated flow below, thus making it highly unstable. Already at low driving temperature of the bottom wall, the fluid becomes unstable. Vortices are formed above the hot bottom wall and travel up by buoyancy forces. Flow exhibits oscillatory behaviour, which at higher temperatures leads to chaotic and turbulent flow. The phenomenon was simulated using different driving temperatures of the bottom wall, observing the change of flow characteristics for steady to unsteady oscillatory regime and at even higher temperature to chaotic behaviour. Time series of heat flux and field functions were examined by phase portraits to determine the flow regime. A grid independence study and time step analysis was performed to asses the algorithms capability of simulation of unsteady behaviour. Ključne besede: boundary element method, heat transfer, unsteady fluid flow, transport equations Objavljeno: 01.06.2012; Ogledov: 942; Prenosov: 15 Povezava na celotno besedilo |
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16. Boundary domain integral method for high Reynolds viscous fluid flows in complex planar geometriesMatjaž Hriberšek, Leopold Škerget, 2005, izvirni znanstveni članek Opis: The article presents new developments in boundary domain integral method (BDIM) for computation of viscous fluid flows, governed by the Navier-Stokes equations. The BDIM algorithm uses velocity-vorticity formulation and is basedon Poisson velocity equation for flow kinematics. This results in accurate determination of boundary vorticity values, a crucial step in constructing an accurate numerical algorithm for computation of flows in complex geometries, i.e. geometries with sharp corners. The domain velocity computations are done by the segmentation technique using large segments. After solving the kinematics equation the vorticity transport equation is solved using macro-element approach. This enables the use of macro-element based diffusion-convection fundamental solution, a key factor in assuring accuracy of computations for high Reynolds value laminar flows. The versatility and accuracy of the proposed numerical algorithm is shown for several test problems, including the standard driven cavity together with the driven cavity flow in an L shaped cavity and flow in a Z shaped channel. The values of Reynolds number reach 10,000 for driven cavity and 7500 for L shapeddriven cavity, whereas the Z shaped channel flow is computed up to Re = 400. The comparison of computational results shows that the developed algorithm is capable of accurate resolution of flow fields in complex geometries. Ključne besede: fluid mechanics, numerical methods, boundary domain integral method, algorithms, incompressible fluid flow, Navier-Stokes equations, velocity vorticity formulation, segmentation technique, driven cavity flow Objavljeno: 01.06.2012; Ogledov: 1065; Prenosov: 38 Povezava na celotno besedilo |
17. A multidomain boundary element method for two equation turbulence modelsMatjaž Ramšak, Leopold Škerget, 2005, izvirni znanstveni članek Opis: The paper deals with the multidomain Boundary Element Method (BEM) for modelling 2D complex turbulent flow using low Reynolds two equation turbulence models. While the BEM is widely accepted for laminar flow this is the first case, where this method is applied for complex flow problems using ▫$k-epsilon$▫ turbulence model. The integral boundary domain equations are discretised using mixed boundary elements and a multidomain method also known as subdomain technique. The resulting system matrix is overdetermined, sparse, block banded and solved using fast iterative linear least squares solver. The simulation of turbulent flow over a backward step is in excellent agreement with the finite volume method using the same turbulent model. Ključne besede: fluid mechanics, turbulent flow, boundary element method, incompressible viscous fluid, stream function-vorticity formulation, two equation turbulence model, backward facing step flow Objavljeno: 01.06.2012; Ogledov: 1041; Prenosov: 45 Povezava na celotno besedilo |
18. BEM for the two-dimensional plane compressible fluid dynamicsLeopold Škerget, Niko Samec, 2005, izvirni znanstveni članek Opis: In this study, the boundary element method, which has been established for theviscous incompressible fluid motion, is modified and extended to capture the compressible fluid state. The velocity-vorticity formulation of the time dependent set of equations is employed, where the kinematics is given with thePoisson velocity vector equation, while the kinetics is represented with the vorticity transport equation, and the pressure field function is governed by the Poisson pressure scalar equation. The method is applied to consider buoyancy driven flow in closed cavity, differentially heated under large temperature gradients. The ideal gas law is used and viscosity is given by Sutherland law. Ključne besede: fluid mechanics, compressible viscous fluid, natural convection, boundary element method, fluid dynamics Objavljeno: 01.06.2012; Ogledov: 883; Prenosov: 47 Povezava na celotno besedilo |
19. A multidomain boundary element method for unsteady laminar flow using stream function-vorticity equationsMatjaž Ramšak, Leopold Škerget, Matjaž Hriberšek, Zoran Žunič, 2005, izvirni znanstveni članek Opis: The paper deals with the Boundary Element Method (BEM) for modelling 2D unsteady laminar flow using stream function-vorticity formulation of the Navier-Stokes equations. The numerical algorithm for solving a general parabolic diffusion-convection equation is based on linear mixed elements and a multidomain model also known as subdomain technique. Robustness, accuracy and economy of the developed numerical algorithm is shown on a standard case of steady backward facing step flow and a periodic flow past a circular cylinder test case. Ključne besede: fluid mechanics, viscous fluid, unsteady laminar flow, boundary element method, multidomain model, stream function, vorticity formulation, backward facing step flow, flow past a cylinder Objavljeno: 01.06.2012; Ogledov: 1300; Prenosov: 54 Povezava na celotno besedilo |
20. Combined single domain and subdomain BEM for 3D laminar viscous flowJure Ravnik, Leopold Škerget, Zoran Žunič, 2009, izvirni znanstveni članek Opis: A subdomain boundary element method (BEM) using a continuous quadratic interpolation of function and discontinuous linear interpolation of flux is presented for the solution of the vorticity transport equation and the kinematics equation in 3D. By employing compatibility conditions between subdomains an over-determined system of linear equations is obtained, which is solved in a least squares manner. The method, combined with the single domain BEM, is used to solve laminar viscous flows using the velocity vorticity formulation of Navier-Stokes equations. The versatility and accuracy of the method are proven using the 3D lid driven cavity test case. Ključne besede: subdomain boundary element method, laminar viscous fluid flow, velocity-vorticity fomulation, lid driven cavity Objavljeno: 01.06.2012; Ogledov: 952; Prenosov: 46 Povezava na celotno besedilo |