Partially Premixed Flame Stabilization in the Presence of a Combined Swirl and Bluff Body Influenced Flowfield: An Experimental Investigation

Abstract

Optical and laser diagnostic measurements in a nonpremixed model gas turbine (GT) burner have been performed to investigate the effect of an increase in thermal power on the flame stabilization. The model GT burner has a large bluff body base with an annular swirl region, leading to a convergent-divergent flow field at the burner exit. Under the investigated conditions, the flame stabilizes predominantly in the diverging section characterized by the swirl flow with a central recirculation zone. With increasing thermal power, the reverse flow of hot burned gases is strengthened, with the hydroxyl radical (OH) planar laser induced fluorescence (PLIF) images indicating an increase in the temperature of the burned gases. The preferred flame stabilization location coincides with the inner shear layer between the reactant inflow and the reverse flow of hot burned gases. At high thermal power, the flame seems to stabilize in regions of high fluid dynamic strain rate, highlighting the influence of the reverse flowing burned gases in the evolution of the flammable mixture upstream. However, simultaneous and time-resolved measurements of the flow-field and scalar field are needed for direct quantification of this. The results are in agreement with the flame stabilization theories based on partial fuel-air mixing and streamline divergence. The flow is seen to decelerate upstream of the flame front and the flame stabilizes in a region of low velocity, created as a result of heat release diverging the streamlines ahead of it.