Synthetic Turbulence Generation for LES on
Unstructured Cartesian Grids

A. Badry, Cranfield University, 2008

Abstract

A parallel CFD code to solve incompressible fluid flow on unstructured Cartesian meshes has been developed almost from ground up. Turbulence statistics have been computed using the Large Eddy Simulation technique. The new code was subjected to some validation where results are compared to available reference data. An analysis on the iteration and discretisation errors was carried out.

This code was then applied to predict the lid driven cubical cavity flow in at a bulk Reynolds number of 10,000. Three different mesh sizes were used to investigate independence of results on grid size. Amongst others, turbulence statistics were checked against Kolmogorov -5/3 law.

A detailed study of synthetic turbulence methods was carried out and applied to the prediction of flow in a duct with square cross section using an inlet and outflow boundaries. Three different turbulence generation methods were investigated namely the artificial turbulence generation method, random perturbation method and a novel hybrid particle-wave method also termed as the enhanced vortex particle method in this study. The mean and instantaneous field variables together with the turbulence
statistics from each method were compared and analysed.

Finally, the code was used to solve turbulent flow over arrays of wall-mounted obstacles with mesh densities comparable to previous studies. The velocity profiles and vector fields at various locations in the domain were compared to data obtained from recent LES simulations. The artificial turbulence generation case was applied for the first time to produce turbulence at the inlet. The turbulence kinetic energy spectrum distribution agrees well with reference data.