Étude numérique de conditons aux limites en situation de combustion turbulente non prémélangée

Abstract

This work is a numerical study on the turbulent non- remixed flame HMI of Sydney's University. The main objective of this thesis is to analyze the prédictions of the vectorial and scalar quantities as a function of vcuious boimdary conditions applied to the annular flow field. The cases analyzed hère are compared -with expérimental results Daily et al. (1998a). To fulfill the objectives of this thesis, the présent document is divided in three main sections. First, a grid sensitivity analysis is performed on the two main catégories of grid (for first and second order turbulence model) in order to show the effect of the physical discretization on each of the turbulent modeling approach. The second part of this "work consists on a study of the turbulence models, already implemented on ANSYS CFX, that can be used for simulating both inert and reacting flows. Thus, the inert flow of Daily et al. (1998a) is simulated using fîrst and second order closure models modeling approach in order to choose the best model to be used for the reacting case. Also, a first sensitivity case study of the annular boundaries conditions is performed on the non reacting flow. The main and last topic of this thesis features the simulation of the HMI turbulent flame of Daily et al. (1998a). For this reacting case, the modeling of combustion and turbulence is respectively donc by using the flamelet regime hypothesis and the EARSM model. The fnst armular boundary condition analysis is performed by using the expérimental profile of velocities and turbulent energy. Then, to try enhancing the quality of the vectorial and scalar quantities prédiction, the profils of those quantities are imposed to follow a mean uniform distribution. The main différence of this approach is that those imiform profils are applied to grids featuring différent annular channel development length. The goal of this approach is to demonstrate which armular boundary condition would be the most effective to correcfiy predicts the HMI flame quantities. For this study, the vector fields of the reacting case is fîrstly depicted in order to characterize the turbulent stiiicture of the flow. Then the scalars quantities such as mixture fi-action, températures and concentration of chemical species are also analyzed as a function of their respective annulus boundaries conditions. The simulation showed that the usage of the EARSM model in addition to the expérimental annular boundary conditions helped significantly enhancing the prédictions of the non-reacting flow, particularly for the measured stations far away from the bluff-body face. While simulating the reacting flow, using the expérimental boundary conditions had the contrary effect and decrease the quality of the prédictions and the uniform profils cases were the ones that give better results. Overall, the prédictions of températures are generally in good agreement with the expérimental results for ail measured stations. On the other hand, the chemical species concentrations do not follow the same trend and the validity of the prédictions are restricted to a région of 45 mm from the bumer's face.

Date	16 Sept 2010
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Patrice Seers (Supervisor)