Large Eddy Simulation of a dual swirl gas turbine combustor: Flame/flow structures and stabilisation under thermoacoustically stable and unstable conditions

Abstract

A laboratory gas turbine model combustor with dual-swirler configuration is investigated using Large Eddy Simulation (LES) with a flamelet subgrid combustion model. Two partially premixed methane/air flames with different equivalence ratio and thermal power are simulated: one stably burning with an elongated V-shape and another undergoing pronounced thermoacoustic oscillations exhibiting a flat shape. Additionally, both flames feature a hydrodynamic instability in the form of a precessing vortex core (PVC). Detailed comparisons between experimental and LES results show that the different flow and reaction zone structures in these two flames are reproduced well. The various flow dynamics resulting from the PVC and thermoacoustic oscillations are also captured accurately in the simulation. Further analyses on the lifted swirl flame stabilisation using phase averaged statistics at the PVC frequencies reveal that the PVC-induced stagnation points provide an anchoring mechanism for both the stable and unstable flames, although in the latter case large self-excited pressure oscillations are present. It is found that the PVC is significantly influenced by these oscillations, being axially stretched and compressed at high and low pressures, respectively. However, the formation of flame leading edge due to the PVC is robust during these unstable processes and the azimuthal movement of the leading point is found to be strongly correlated with the rotation of the PVC in both flames, further confirming the vital role of the PVC in the stabilisation process of these lifted swirl flames.

The Role of CFD in Modern Jet Engine Combustor Design

“…Recent findings [20,21] show that, since part of the strain is resolved in the LES, its effect on the flame is implicitly captured as long as the local mesh size is appropriate. These preliminary findings have been confirmed by GT calculations [22][23][24] and show that strained flamelets are unnecessary at least for the conditions considered. For an industrial perspective where the reduction of computational cost is essential, these recent findings open the way to effective use 1 The flame brush is the time-averaged high temperature region.…”

“…The dual-swirl GTMC experimentally investigated by Meier et al [50,51] at the German Aerospace Center (DLR) is of interest. The schematic of this GTMC [50,51] and a typical computed flame surface using LES [24] are shown in Figure 1. This burner has a single nozzle head with dual-swirl air passages, which is a common design in modern jet engines to achieve fast fuel-air mixing.…”

“…One recent development in this sense is the SDR closure of Dunstan et al [41], which approaches the linear relaxation concept in the limiting behaviour of non-reactive mixture and is thus more recommended. This model has been used in many past studies for different combustion regimes [20,22,24,36] (see also Sections 3 and 4).…”

A scaling law for the recirculation zone length behind a bluff body in reacting flows

“…The use of this model for partially premixed combustion has also been developed by Chen, Ruan & Swaminathan (2017) and applied for gas turbine combustors (Chen et al. 2019 a , b ; Langella et al. 2018 a ).…”

“…2018 a ; Chen et al. 2019 a , b ) with and without thermo-acoustic instabilities. Furthermore, this s.g.s.…”