LES Combustion Model With Stretch and Heat Loss Effects for Prediction of Premix Flame Characteristics and Dynamics

Abstract

The present paper extends an approach to include effects of stretch and heat losses into turbulent combustion models from the RANS framework to the LES framework. This approach has shown the potential to improve the prediction of flame stabilization by considering these combined effects. The model is based on the calculation of the consumption speed of laminar premixed flames influenced by variations in strain and heat loss in asymmetric counterflow configurations. The consumption speed depending on strain and heat loss is introduced into a turbulent combustion model based on a progress variable approach. Large Eddy Simulations of a fully-premixed axial swirl burner with and without the influence of stretch and heat loss effects are carried out and validated against flow field and OH* chemiluminescence measurements for different power ratings and equivalence ratios. Flame dynamics are also investigated by extracting the Flame Transfer Function of the fully-premixed axial swirl burner with System Identification methods. Good agreement on the flow field, flame characteristics and dynamics between experiment and simulation was obtained with the inclusion of stretch and heat loss effects into the combustion model. Results show the importance of including these effects into turbulence combustion models for the design of premix burners for gas turbine combustors.

Numerical Modeling of Gaseous Partially Premixed Low-Swirl Lifted Flame at Elevated Pressure

“…Despite the model was originally proposed in RANS framework, the rationale behind it can be extended to LES without particular modifications. However, the two approaches deeply differ in the flame stretch modelling, which was here inspired by previous works focused on the Turbulent Flame Closure [33][34][35]. The present work represents the extension of the Klarmann's model [27] to Large Eddy Simulation, adopting and improving the quenching effects formulation in [33][34][35] thanks to the modelling of the front curvature contribution on the flame stretch.…”

“…In LES framework, the above definition can be filtered and the two terms of a and curvature σ c distinguished. Applying the filter to the strain definition leads to [33]:…”

“…Nevertheless, the flame stretch definition requires the calculation of the front curvature σ c . Despite in previous LES studies it was not modelled [33][34][35]37], in this work this contribution was included by filtering its definition:…”

Impact of Stretch and Heat Loss on Flame Stabilization in a Lean Premixed Flame approaching Blow-off

“…Finally, the source term of progress variable has been modelled in the present work with either the Zimont Turbulent Flame Closure (TFC) or an extended TFC model able to deal with the effects of both flame strecth and heat loss. The extension of TFC model is implemented in Fluent following the approach of Tay-Wo-Chong et al [11]. The model relies on the empirical correlation (1) for the flame consumption speed developed by Tay-Wo-Chong et al [12] from 1D calculations of strained lean premixed methane-air flamelets in asymmetric counterflow configuration at atmospheric pressure:…”

“…The first two effects enters respectively in the stretch Karlovitz number Ka and in the heat loss parameter ϕ. For more details about the model implementation see the formulation of Tay-Wo-Chong et al [12,11].…”