Measurements and LES of a SGT-800 Burner in a Combustion Rig

The Siemens gas turbine SGT-800 is the largest industrial gas turbine produced by Siemens Industrial Turbomachinery (SIT) offering a dry low emission (DLE) capability below 15 ppm NOx. It has a very high reliability using an annular combustor system with passive damping and 30 DLE burners. To obtain a greater understanding of the mixing process and the flame dynamics and in order to further reduce the emission levels, single burner rig tests have been performed. The laboratory measurements are complemented by Large Eddy Simulation (LES) and Reynolds Averaged Navier-Stokes (RANS) simulations to further investigate the transient fuel distribution and subsequent flame behavior.

The measurements were performed jointly by SIT and Lund University using the SIT single burner combustion rig, where the square chamber allows great optical access in the flame region. The experimental data includes wall temperature, pressure fluctuations, light intensity variation and simultaneous Planar Laser Induced Fluorescence of OH and acetone. This investigation is complemented using fuel concentration field laser measurements of the fuel distribution upstream of the flame region in SIT water rig, using a burner partly made of Plexiglas to allow for optical access.

The LES model was developed jointly by SIT and FOI. The LES computations were performed using a combustion code developed from the OpenFOAM library utilizing the mixed subgrid flow model, complemented with a subgrid wall model. The reacting flow was simulated using a Finite Rate Chemistry (FRC) combustion model based on the Partially Stirred Reactor (PaSR) model. For this study, a two-step global/reduced methane-air reaction mechanism was employed to describe the combustion chemistry. The RANS simulations were performed with ANSYS Fluent, using the k-ε Realizable eddy viscosity turbulence model in combination with the Fluent partially premixed combustion model. This model is a combination of the Zimont flamelet progress variable model and a Probability Density Function based non-premixed combustion model.

The investigation includes a detailed evaluation of the numerical results compared to the measurement data. The numerical model includes the upstream air supply and fuel line systems up to well-defined constrictions to ensure appropriate acoustic inlet conditions. The measurements reveal large fluctuations in the flame region, which has been investigated using LES.