Parametric study of vortex structures and their dynamics in swirl-stabilized combustion

The dynamics of major flow structures were studied in a gas turbine model combustor for perfectly premixed swirlstabilized flames under a variety of reacting and non-reacting conditions using high-repetition-rate laser diagnostics. The studied combustor is a target case for the International Workshop on Advanced Measurement Techniques and Computational Methods for Premixed and Partially Premixed Combustion. Measurements were taken of the three-component velocity field, OH planar laser induced fluorescence, and OH* chemiluminescence at a rate of 10 kHz for nine different flow conditions, covering a range of thermal powers (Pth = 10 − 35 kW) and equivalence ratios (φ = 0.65 − 0.8). Under all non-reacting conditions, the dominant flow structure was a helical vortex core (HVC) that rotated around the burner at a frequency represented by a constant Strouhal number StH,NR = 0.78. However, igniting the burner significantly altered the flow structures. At most conditions, the strength and frequency of the HVC increased relative to the corresponding non-reacting case. The HVC frequency in such cases was once again represented by a constant Strouhal number of StH,R = 0.88, irrespective of the thermal power or equivalence ratio. The HVC frequency was considerably higher than the frequency of the self-excited thermo-acoustic oscillations exhibited by the burner. However, at other conditions, combustion prevented formation of the HVC. In such cases, the dominant flow structure dynamics were periodic shear layer oscillations and shedding of toroidal vortices at the thermo-acoustic frequency. Cases in which combustion prevented formation of the HVC included those at low thermal powers (Pth ≤ 15 kW) and the highest equivalence ratio (φ = 0.8). A distinct relationship was found between the flow structure geometry and the pressure oscillation amplitude, with cases having an HVC resulting in higher pressure oscillations.