engleski

Implicitly Coupled Turbulence Models

Introduction Implicitly coupled pressure- velocity algorithms for incompressible flows introduced a significant increase in convergence rates for the velocity and pressure equations, compared with corresponding segregated algorithms (e.g. SIMPLE or PISO). However, when implicitly coupled solvers are used for turbulent fl ow simulations, convergence rates are often limited by segregated treatment of turbulence model equations. Despite their relatively simple mathematical representation, turbulence model equations present serious numerical difficulties, among which are non- linear coupling, convergence and positivity preserving challenges. Furthermore, in the process of convergence, non- physical solutions, namely negative values of the turbulence quantities may appear even if the equation set analytically guarantees to remain positive. Therefore, stability and boundedness of the implemented turbulence models is becoming an active and challenging field for research. Aims The aims of this work is to derive general conclusions regarding impact of implicit coupling of two-equation turbulence models on overall calculation performance. Methods The method was previously implemented in foam- extend (the community-driven fork of OpenFOAM) using incompressible k-epsilon and k-omega SST models and it was successfully validated for the backward facing step and for the NACA 4412 case. The previous benchmark study was carried out on structured and relatively small grids, therefore the new analysis will contain benchmarking on large three-dimensional unstructured grids. Furthermore, the comparisons will be carried out for both implicitly coupled and segregated pressure-velocity algorithms in order to obtain a general conclusion about influence of implicit coupling of turbulence models on overall calculation performance. Expected scientific contribution The work is suppose to quantify the trade-off between the performance enhancements and increased memory usage when implicit turbulence models are used for industrially applicable flow problems.

Block Coupled Solvers ; Turbulence Modelling ; Benchmarking

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