Modelagem matemática de escoamentos reativos turbulentos utilizando uma metodologia hibrida LES/PDF

Abstract

The present work is devoted to the development and implementation of a computational framework to perform numerical simulations of low Mach number turbulent reactive ows. The numerical algorithm designed for solving the transport equations relies on a fully implicit predictor-corrector integration scheme. A physically consistent constraint is retained to ensure that the velocity eld is solved correctly, and the numerical solver is extensively veried using the Method of Manufactured Solutions (MMS) in both incompressible and variable-density situations. The nal computational model relies on a hybrid Large Eddy Simulation / transported Probability Density Function (LES-PDF) framework. Two dierent turbulence closures are implemented to represent the residual stresses: the classical and the dynamic Smagorinsky models. The specication of realistic turbulent in ow boundary conditions is also addressed in details, and three distinct methodologies are implemented. The crucial importance of this issue with respect to both inert and reactive high delity numerical simulations is unambiguously assessed. The in uence of residual sub-grid scale scalar uctuations on the ltered chemical reaction rate is taken into account within the Lagrangian PDF framework. The corresponding PDF model makes use of a Monte Carlo technique: Stochastic Dierential Equations (SDE) equivalent to the Fokker-Planck equations are solved for the progress variable of chemical reactions. With the objective of performing LES of turbulent reactive ows in complex geometries, the use of distributed computing is mandatory, and the retained domain decomposition algorithm displays very satisfactory levels of speed-up and eficiency. Finally, the capabilities of the resulting computational model are illustrated on two distinct experimental test cases: the rst is a two-dimensional highly turbulent premixed ame established between two streams of fresh reactants and hot burnt gases which is stabilized in a square cross section channel ow. The second is an unconned high velocity turbulent jet of premixed reactants stabilized by a large co- owing stream of burned products.