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Turbulence and scalar flux modelling applied to separated flows


Respondent	Huvudhandledare	Bihandledare	Datum
Johan Gullman-Strand	Arne Johansson	Gustav Amberg	2004-12-17

Opponent
Suad Jakirlic, TU Darmstadt

Betygsnämd
Peter Eliasson, KTH, Mekanik Antti Hellsten, HUT Christoffer Norberg, LTU

Abstract

The turbulent flow in an asymmetric diffuser has been studied by the means of Reynolds averaged Navier-Stokes equations with both differential and explicit algebraic expressions to model the Reynolds stress tensor. Modifications to the differential stress model have been derived, using the inverse turbulence timescale to obtain the dissipation of turbulence kinetic energy. The explicit algebraic Reynolds stress model has been used in combination with a two-equation platform to close the system of equations. Modifications made to the transport equation for the inverse turbulence timescale has made it possible to substantially relax the demand on near-wall resolution of this quantity. The rapid growth present in the original formulation can be treated as an explicit function of the wall-normal distance. In order to use the new formulation for the transport equation, an equation has been derived to obtain the shortest distance between a point and the closest wall, regardless of the geometric complexity of the domain. An explicit algebraic expression to model the passive scalar flux vector has been investigated using a comparison with a standard eddy-diffusivity model in the asymmetric diffuser. Results show a substantial improvement of the complexity of the scalar field and scalar flux vector in separated flows. Automated code generation has been used in all the above studies to generate versatile model testing tools for general two-dimensional geometries. Finite element formulations are used for these tools.
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