Modelling of a turbulent lean premixed combustor using a Reynolds-averaged Navier–Stokes approach

• Published in: Journal of the Brazilian Society of Mechanical Sciences and Engineering 2020, Vol.42 (5), Article 213
• Main Authors: Coimbra, Alain P. N., Figueira da Silva, Luís Fernando
• Format: Article
• Language: English
• Subjects: Aerodynamics; Boundary conditions; Combustion chambers; Computational fluid dynamics; Computer simulation; Engineering; Engineering Sciences; Finite element method; Fluid flow; Gas turbine engines; Gas turbines; Grid refinement (mathematics); Isothermal flow; Jet engines; Large eddy simulation; Mathematical models; Mathematics; Mechanical Engineering; Navier-Stokes equations; Numerical Analysis; Reactive fluid environment; Reynolds averaged Navier-Stokes method; State-of-the-art reviews; Swirling; Technical Paper; Topology; Transport equations; Turbulence; Turbulent flow; Velocity distribution
• ISSN: 1678-5878; 1806-3691
• DOI: 10.1007/s40430-020-2273-y

This work aims to characterize lean premixed turbulent swirling flames representative of gas turbines and jet engines via a numerical study of flame topologies in a laboratory-scale burner. The state of the art of the numerical studies concerning these types of flames is first reviewed, with respect to Reynolds-averaged Navier–Stokes and large eddy simulations. Then, a turbulent, isothermal flow study is performed within the radial swirler. The impact of mesh refinement levels and boundary conditions on the swirl number and overall flow structure is investigated. The mesh refinement level and slip wall boundary condition alter the computed swirl number significantly. The computed swirl number converges to a value of 0.7, which is larger than the geometrical one, 0.4. Furthermore, using Reynolds-averaged Navier–Stokes transport equations, closed by the realizable k - ϵ model, coupled with a two-equation premixed combustion model for methane/air mixtures, two combustion regimes are analysed. These regimes correspond to the outer recirculation zone flame and an unstable regime. The flow structure is characterized in terms of velocity fields, turbulence and combustion properties. A reaction progress variable comparison is also performed, using existing experimental results, yielding qualitatively similar structures for both studied regimes. Some discrepancies between numerical and experimental results concerning the stable regime may be observed: The computed progress variable at the outer recirculation zone, 0.5, is smaller than the experimental value, 0.8, and the average flame brush thickness, 1 mm, is found to be smaller than the measured, 3 mm.