טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentSreekanth Ravindran
SubjectLarge Eddy Simulation of Turbulent Flame Wall-Interactions
DepartmentDepartment of Aerospace Engineering
Supervisors Professor Emeritus Yeshayahou Levy
Professor Emeritus Jerrold Greenberg
Full Thesis textFull thesis text - English Version


Abstract

The aim of the present research work is to investigate Turbulent Flame-Wall Interactions (TFWI) in non-premixed combustion using Large Eddy Simulation (LES). The interaction between turbulent flame and wall is an important phenomenon, affecting flame stability, emissions and wall heat transfer. In the present work a parallel LES combustion finite-volume code was developed to simulate turbulent flame-wall interactions. First, a novel fast Riemann solver using the blending of Riemann Invariants was developed and applied in the code. The Riemann solver was tested for various cases of shock tube problems and two dimensional Riemann problems and was found to be extremely accurate in capturing discontinuities and highly computationally efficient. The non-reacting LES code was validated by testing it on standard test cases such as a free jet, flow past a backward facing step and flow in a ramjet dump combustor and was found to be reasonably accurate when compared with independent experimental data. A new approach for modeling non-premixed combustion was used in the present work. The Flame Surface Density combustion model was adapted to the LES framework, modified with suitable closure models, and implemented to simulate non-premixed combustion in a dump ramjet combustor. The simulation was compared to experimental results from the literature and was found to be in sound agreement with experimental data. In order to incorporate the effect of wall interactions with the flame a Flame-Wall Interaction model was adapted, modified and used in the flame surface density framework. The model was found to be successful in predicting the extinction of the flame under quenching conditions. A comprehensive investigation was carried out to study phenomena of quenching of flamelets at the wall, and temporal and spatial changes in heat transfer due to flame wall interaction for various wall temperatures. Cold walls were found to severely inhibit proper ignition of the reaction mixture resulting in complete extinction of the flames due to large heat loss to the wall. Large unsteady heat fluxes were found to be generated near the wall just before extinction. A comprehensive combustion regime analysis was carried out and it was observed that the cold walls affected the turbulence, and hence scalar dissipation rates, lowering the reaction rates and resulting in flame extinction.