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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.

Influence of air staging on the dynamics of a precessing vortex core in a dual swirl gas turbine model combustor