Large Eddy Simulation of turbulent flames in a Trapped Vortex Combustor (TVC) – A flamelet presumed-pdf closure preserving laminar flame speed

Abstract

Flow and flame dynamics inside a trapped vortex combustor are analyzed from Large Eddy Simulation (LES) results compared against measurements. The Navier-Stokes equations are solved in their fully compressible form over a Cartesian grid resorting to immersed boundaries to account for the complex geometry, composed of an annular flow impacting a set of axisymmetric rods (flame holders) before interacting with a cavity. Various cases are considered, varying the main flow rate, the length of the cavity, injecting secondaryair and also adding a swirling motion. From these cases, three main cavity flow regimes emerge. The modeling of molecular diffusion in LES with presumed probability density function (pdf), as filter of premixed flamelets, is also discussed. It is shown that a dynamic correction to molecular diffusion may be computed from the pdf control parameters to ensure the correct laminar flame speed, whatever the mesh used. Finally, studying the turbulent flame evolution within the cavity in the various cases, suggests that swirling motion is mandatory to favor the global burner stability.

Large Eddy Simulation of premixed turbulent combustion using approximate deconvolution and explicit flame filtering

“…As discussed in [28], the application of a corrective factor to the diffusive fluxes may be generalized to any modeled expression of the burning rate _…”

A review of computational studies on trapped vortex combustors for gas turbine applications

“…Reactive and non-reactive studies have been carried out using LES technique to explore the impact of main flow rate, impact of cavity injection and the impact of swirl motion in the TVC (Merlin et al , 2011). In the reactive case, LES simulations were carried out to demonstrate the ability of the LES technique to capture the flame structure inside the cavity of TVC (Merlin et al , 2012). The LES simulations, involving second and fourth order artificial dissipative terms increases the accuracy of convective flux in the simulations while considerable reducing the computing power when compared to addition of explicit dissipative terms.…”

“…The geometry includes a fore body and an afterbody with slots. Cavities with equal forebody and afterbody diameter were studied in the works of Merlin et al (2011Merlin et al ( , 2012, Wang et al (2013) and Xavier et al (2015bXavier et al ( , 2015a. TVC with more than one afterbodies was studied by Di Nardo et al (2009) and Wang et al (2013).…”

“…The numerical scheme used in the reactive flow cases is third-order accurate and hence resulted in very low diffusion error when compared to the usual practice of using second-order schemes. LES techniques using SiTCom parallel flow solver coupled with explicit finite volume scheme for cartesian grids were used in the simulations to study reactive and nonreactive cases (Merlin et al, 2011(Merlin et al, , 2012. Much simpler approximation using RANS with k-v turbulence model for non-reactive cold flow cases were also used (Selvaganesh and Vengadesan, 2008;Zeng et al, 2019).…”

Laminar Flame Speed Model at the Initial Stage of Formation Diffusion Flame

“…By considering the accuracy of predication of laminar flame speed and Markstein length from the spherical flame method, he suggested different non-linear models could be e used for different mixtures. In terms of large eddy simulation (LES) using sub-grid scale modeling, a methodology was suggested by [5]. It was proposed that a dynamic correction to molecular diffusion of the progress variable used in a presumed probability density function approach may be determined from the pdf control parameters to ensure the correct laminar flame speed used in with premixed flamelets model.…”