Unsteady RANS for Simulation of High Swirling Non-Premixed Methane-Air Flame

Abstract

Highly swirled non-premixed methane-air combustion is studied using Unsteady RANS. The increased CPU power at present times makes RANS solutions a viable design methodology for industrial applications. LES, Large Eddy Simulation, is still a bit far away from being the routine approach as a design tool in industry. The confined non-premixed TECFLAM S09C flame is investigated because of its similarity with gas turbine engine combustors. A block structured hexahedral computational mesh is used for the whole domain for higher numerical accuracy. A first-order accurate Euler Implicit technique is used for the temporal discretization of the transient terms. Realizable k-ε turbulence model is employed in order to account for the turbulent flow effects on the flow field and chemical reactions. Results of fast and two step reactions are compared with finite rate chemistry. Results show that, the best solution is obtained by using Finite Rate Eddy Dissipation Model.The infinitely fast chemistry approach is not capable of predicting the reaction delay that is clearly observed in the experiments. Instead, the fast chemistry approach show reaction zones in the close vicinity of the swirler where the fuel-air mixing is not well achieved for the reactions to take place in such a short distance. The flow field is directly affected by the heat release rate that is determined by the fuel air mixing and combustion model. Nomenclature S= swirl number ρ = density U = velocity U θ ,W = circumference velocity U r ,u = axial velocity A = area k = kinetic energy ε = eddy dissipation rate R = swirler radius D = swirler diameter r = radial location CRZ = central recirculation zone EDM = eddy dissipation model