Claudiu Dem

Experimental Study of Turbulence-Chemistry Interactions in Perfectly and Partially Premixed Confined Swirl Flames

Abstract A gas turbine model combustor (Turbomeca Burner) for premixed methane/air flames has been operated at atmospheric pressure in two different modes of premixing. In the partially premixed mode, fuel was injected into the air flow within the swirl generator shortly upstream of the combustion chamber while in the perfectly premixed mode fuel and air were mixed far upstream. The main objective of this work is the study of the influence of the mode of premixing on the combustion behavior. Stereoscopic particle image velocimetry has been applied for the measurement of the flow field, OH chemiluminescence imaging for the visualization of the flame shapes and single-shot laser Raman scattering for the determination of the joint probability density functions of major species concentrations, mixture fraction and temperature. The mixing and reaction progress and effects of turbulence-chemistry interactions are characterized by scatterplots showing the correlations between different quantities. To isolate effects of mixing from combustion instabilities that were frequently observed in this combustor, operating conditions without thermo-acoustic oscillations or coherent flow structures were chosen. While the mode of premixing had no major influence on the general flame behavior characteristic differences were observed with respect to flame anchoring, the flow field in the inner recirculation zone and the CO concentration level. The results further extend the data base of previous experimental and numerical investigations with this burner.

Influence of Air Staging on the Dynamics of a Precessing Vortex Core in a Dual-Swirl Gas Turbine Model Combustor

Detailed laser diagnostic and optical measurements to study temperature, major species concentration, velocity field and flame shape, have been carried out in a partially premixed dual-swirl gas turbine model combustor (GTMC) at atmospheric pressure using methane as fuel. The GTMC features separate air plenums for the inner and outer air stream, thus allowing control of the air split ratio between the inner and outer air stream. In the current study, flames with a thermal power of 22.5 kW and a global equivalence ratio of φ = 0.63 have been studied for air split ratios L between 1.2 and 2.0, with L = 1.6 corresponding to equal pressure loss across both swirlers. Temperature and major species concentrations were measured with laser Raman scattering, the velocity field with particle image velocimetry (PIV) and the flame shape and position with OH* chemiluminescence. For all air split ratios, the flame did not exhibit strong thermo-acoustic oscillations, such that the global heat release rate did not vary with time. However, due to a precessing vortex core (PVC) that was present for all operating conditions, strong variations in the local heat release distribution of the flame could be observed. The frequency of the PVC was at a constant Strouhal number, which was based on the air mass flow through the inner air nozzle, but was independent of the air split ratio. The Strouhal number for the PVC was Srnr = 0.78 for the non-reacting case and Srr = 0.85 for the reacting case. The current paper focuses on (a) providing a detailed data set for the validation of numerical simulations of this combustor and (b) on the influence of the air split ratio on the dynamics of the PVC.