The effect of transversal velocity fluctuations on the thermoacoustic response of reheat flames

Abstract

Thermoacoustic analysis remains a key component during the development process of new combustion chambers. Whereas a vast amount of literature exists on the interaction of planar acoustic and propagation-stabilized flames, research on reheat flames, especially, on how they respond to transverse modes is scarce. With the study presented here, we show the isolated effect of transversal velocity perturbations on a reheat flame. This is done for two distinct flame stabilization cases occurring in a lab-scale reheat combustor. For the first, the flame is partly autoignition-stabilized but also has propagation-stabilized regions in the shear layer because of recirculation zones induced by a backward-facing step. The second features only a minimal step height and therefore only minor recirculation zones, leading to an almost purely autoignition-stabilized flame. The two different flame stabilization cases are investigated using Reynolds–averaged Navier–Stokes simulations integrating an in-house reheat combustion model. The analysis shows that transverse velocity perturbations have no effect on flames that are purely stabilized by autoignition. In the presence of propagation-stabilized flame regions within the shear layer, transverse velocity perturbations do induce heat release rate fluctuations, as expected.