Abstract
This thesis is the result of a research activity carried out in collaboration between the Aerospace Engineering Department of the University of Pisa and INRIA, aimed at developing numerical tools and methodologies for the numerical prediction of complex flows, characterized by massively separated unsteady wakes and complex geometry, as encountered in many applications of engineering and industrial interest.
In this work, a systematic investigation on the effects of some of the factors that affect the results of variational-multiscale and classical LES is started in the simulation of time-evolving shear-layers. These are a rather classical flow configuration for direct numerical simulation (DNS) and LES and, thus, detailed reference data have been available in the literature. Thanks to pe-riodic boundary conditions and the consequent limited streamwise width of the computational domain, the simulations are significantly less demanding than those of spatially evolving flows, as for instance bluff-body flows, and this allows simulations to be carried out for a significant number of parame-ter values. It has also been possible to obtain, at reasonable computational costs, a well-resolved Direct Numerical Simulation, useful for making a com-parison with the successive simulations.
In a first time, the sensitivity of the results to the amount of numerical vis-cosity introduced has been tested in the so-called implicit LES : the analysis highlighted the capabilities of these simulations when progressively coars-ening the grid, and, moreover, the characteristics of the numerical methods adopted. In a second part, LES and VMS-LES simulations have been carried out using Smagorinsky and WALE subgrid scale models. An analysis of the sensitivity to the grid refinement has been carried out. As it regards all the other parameters involved in LES and VMS-LES, no particular adaptation to the considered test-case has been made.
