PIV/PLIF investigation of unsteady turbulent flow and mixing behind a model gas turbine combustor

The present paper reports on the investigation of turbulent transport and fuel mixing under nonreacting conditions for a model gas-turbine swirl burner based on a design by Turbomeca. Two regimes of fuel (methane with acetone vapor) injection are compared. Specifically, the injection between the vanes of the radial swirler organizes lean, well-premixed combustion in a primary zone. The fuel supply as a central jet from the swirler’s centre-body provides a pilot flame. A combination of stereoscopic PIV and acetone PLIF systems is used to measure the velocity and concentration fields in the flows with a Reynolds number of 3 × 10⁴. The effect of the central jet density is tested by replacing methane with air and neon. The data are processed using the POD method to extract coherent flow structures and quantify large-scale variations in concentration produced by them. In both cases, the flow dynamics were associated with the movement of large-scale vortex structures in the inner and outer mixing layers. The coherent flow fluctuations provide a substantial contribution to the turbulent transport, which locally exceeds 60% for the Reynolds shear stresses and Reynolds fluxes. The mixing is analysed based on the local probability of the fuel concentration pulsations. The probability distributions for the coherent and stochastic components of the pulsations are considered separately. For the premixed operation regime, the variation in the local equivalence ratio at the nozzle exit of the swirl burner reached 35% with the contribution of coherent pulsations up to 7%. In contrast, the large-scale vortex structures for the diffusion pilot jet flame primarily contributed to the advection of the fuel but not mixing. This paper provides relevant data for validating numerical methods for simulating unsteady turbulent mixing in swirl combustors.