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A multidomain boundary element method for unsteady laminar flow using stream function-vorticity equations
Matjaž Ramšak, Leopold Škerget, Matjaž Hriberšek, Zoran Žunič, 2005, original scientific article

Abstract: 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.
Keywords: fluid mechanics, viscous fluid, unsteady laminar flow, boundary element method, multidomain model, stream function, vorticity formulation, backward facing step flow, flow past a cylinder
Published in DKUM: 01.06.2012; Views: 2246; Downloads: 105
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Simulation of unsteady fluid flow and heat transfer by BEM
Jure Ravnik, Leopold Škerget, 2011, published scientific conference contribution

Abstract: 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.
Keywords: boundary element method, heat transfer, unsteady fluid flow, transport equations
Published in DKUM: 01.06.2012; Views: 1980; Downloads: 29
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