Kay Wittig

Three-dimensionality of fluid flow in the benchmark experiment for a pure metal melting on a vertical wall

This work is devoted to the two- and three-dimensional modeling of pure Gallium melting in a cuboid cavity, as has been studied experimentally by Gau and Viskanta (C. Gau & R. Viskanta. J. Heat Transfer 108, pp. 171-174, 1986). The geometry and boundary conditions used in this work are taken from the benchmark experiment. The fixed-grid technique with artificial porosity was implemented into a finite-volume code, where the pressure-velocity coupling was treated using the SIMPLE algorithm. The results of simulations showed that the so-called multicellular flow pattern occurs only in two-dimensional (2D) simulations at the beginning of melting. However, an analysis of three-dimensional simulations (3D) showed the absence of a multivortex structure at any time step. This fact is explained by the presence of walls in the third direction which suppress the flow and by the occurrence of weak turbulence in the bulk of the melt preventing the formation of the long-living multicellular flow pattern known from previous 2D simulations. Additionally, we studied the influence of the cuboid width on the flow structure and solid front shapes. The results are discussed.

3D numerical study on the influence of particle porosity on heat and fluid flow

This work is devoted to the three–dimensional numerical simulations of the heat and fluid flow past and through a porous spherical particle over a wide range of Reynolds numbers (20 100) a local maximum in the drag force coefficient was observed for a porosity of about 0.76. On the basis of the results of simulations, expressions are derived and examined for the drag coefficient and the surface–averaged Nusselt number.

Parallelization of the 3D SIP algorithm

In this work an algorithm for the parallelization of the three dimensional strongly implicit procedure (3DSIP) matrix solver is presented. The algorithm is based on the block Jacobi algorithm. The parallelization of the matrix solver is implemented with the OpenMP standard. The speedup of this algorithm is demonstrated using the numerical solution of a 3D Laplace equation and a 3D Navier Stokes equations applied to a lid driven cavity problem.

Modelling of pore growth in char particles by an octree-based 3D PLIC method

A geometrical algorithm for Piecewise-Linear Interface Calculation (PLIC) is used on a 3D octree-based hexa-hedral mesh in order to reconstruct the surface and macropores of a porous char particle. The algorithm is then applied on simulating moving surfaces and particle consumption of char particles reacting with a carbondioxide and water atmosphere under kinetically controlled conditions. Depending on the initial pore configuration different developments of the specific particle surface due to pore surfaces interactions are observed.