Abstract
Computational prediction of thermoacoustic instabilities arising in gas turbine and aero-engine combustors still remains a challenge especially if fuel is injected in a liquid spray form. This study shows that, in LES of such a combustor, the treatment of the liquid fuel film created on the walls of the injection system affects the mean flame weakly, but modifies the flame dynamics strongly. The configuration used for this work is the experimental setup SICCA-spray available at EM2C laboratory in Paris. First steady spray flame measurements are used to validate the LES Euler-Lagrange approach. Two modelling strategies for the interaction between the liquid fuel and the injector walls are tested with a negligible impact on the flame shape and structure. In the second part the same comparison is applied to another operating condition where a self-sustained thermo-acoustic limit-cycle is experimentally observed. In that case resonant coupling is achieved with LES, confirming the adequacy of the approach but only when the film layer is taken into account. Indeed, contrarily to the stable configuration, the difference between the two Lagrangian boundary conditions is shown to have a major impact on the feedback mechanism leading to the thermoacoustic oscillation.
Highlights
Modern gas turbines operating in lean conditions to reduce the production of pollutants, such as NOx, are known to be prone to thermoacoustic instabilities, which in extreme cases lead to fatal failure of the engine [1]
The mean axial velocity peak as well as the intensity of the central recirculating zone (CRZ) are well captured by Large Eddy Simulation (LES) (Fig. 7) in the three planes
The lean two-phase swirled flames of the SICCA-spray experiment is simulated by use of a Lagrangian LES formalism for both the steady and self-sustained limit-cycle operating conditions
Summary
Modern gas turbines operating in lean conditions to reduce the production of pollutants, such as NOx, are known to be prone to thermoacoustic instabilities, which in extreme cases lead to fatal failure of the engine [1]. The second approach is to adopt the Lagrangian framework which solves the trajectory for each particle introducing difficulties such as load balancing because of the particle motion in the gaseous field [19] and their non-uniform distribution in the computational domain or the treatment when reaching the boundaries This approach has been applied to many realistic LES applications with multiple aims like ignition [20] or stabilized flames [14] as well as thermoacoustic instabilities [21]. In this case, correctly reproducing the liquid droplet behavior is a key aspect, since the feedback loop between the acoustic field and the flame is coupled to the particle dynamics [22, 23]. Spray [27, 28]
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