Validation of a Novel LES Approach Using Tabulated Chemistry for Thermoacoustic Instability Prediction in Gas Turbines

Abstract

For the prediction of thermoacoustic instabilities in gas turbines, a compressible, unsteady LES approach was validated for 1D, lab-scale and technical-scale test cases. The simulations were performed with a novel combustion model, which relies on a combination of tabulated chemistry and flame thickening. A 1D case was used for fundamental verification and to quantify the mesh resolution dependent error. The verification demonstrated sufficiently accurate predictions. In a second step an elevated pressure lab-scale flame was considered to calibrate the model parameter of the turbulence chemistry interaction at relevant conditions. For this case CO2 field data measured with the Raman scattering method is available. Finally, a test rig configuration of a can type combustor was investigated. The comparison between experiment and simulation was performed in terms of thermoacoustic pressure amplitudes at stable and unstable operating conditions. The LES combustion model relies on an artificial thickened flame approach to ensure that the flame propagation speed is reproduced with tolerable error. Tabulated chemistry provides the source term for CO2 (governing species) as a function of the mixture fraction and the CO2 concentration based on premixed, laminar flamelets. The model distinguishes between inherent thickening due to sub grid scale turbulence and explicit laminar thickening. This novel thickening approach is presented for the first time. The presented approach was able to predict the thermoacoustic stability behavior of a gas turbine combustion system correctly.

Coupling multicomponent droplet evaporation and tabulated chemistry combustion models for large-eddy simulations

“…The combustion model, developed initially for methane combustion by Dederichs [54], is a combination of the FGM and the SCRS models in order to have a compromise between the computational cost, the size of the tables and the accuracy of the simulations. One dimensional laminar flames are calculated prior to the simulation, using an appropriate kinetic mechanism, and the results are written into tables based on the passive scalars controlling the flame structure.…”

“…The perfect gas equation of state is used by the solver, so that deviations from the ideal law are not taken into account. Further details on the solved equations, the artificial flame thickening or the flame-turbulence interaction models can be found in [54].…”