Experimental analysis of the flowfield at the exit of a premixer for combustion applications

The flowfield at the exit of a premixer for combustion applications is experimentally studied under isothermal conditions. The premixer produces a main swirling flow, while an injector, positioned on the jet axis, generates four jets in cross-flow mimicking the fuel introduction. The main nozzle has a variable geometry to simulate different operative conditions. Two configurations, in which the flow rate of the fuel cross-flow jets is varied, are examined. Mean and fluctuating streamwise velocity profiles, acquired by means of laser Doppler anemometry (LDA) at the exit plane of the premixer, are presented for all of the geometrical setups and compared with the surrogate fuel distribution at the exit plane. The mixing characterization is provided either by means of an intrusive gas sampling technique and non-intrusive flow-visualization analyses. Results show that the velocity flowfield is considerably affected by the relative strength of the fuel jets with respect to the main swirling flow, and by the boundary conditions at the nozzle exit. Comparison of the mixing and velocity data shows that for some configurations there is a matching between the streamwise velocity momentum and scalar distributions. Correspondingly, the fuel jets at the exit plane maintain a marked individuality.