Direct numerical simulation of turbulence modulation by premixed flames in a model annular swirling combustor

Direct numerical simulations (DNS) of two adjacent turbulent swirling kerosene/air premixed flames in a model annular combustor under aircraft engine-like conditions are carried out to investigate turbulence modulation by flames. One inert case and two reactive cases with different Reynolds numbers and Karlovitz numbers are studied. Most characteristic non-dimensional parameters of the reactive cases are designed to be close to those of the realistic aircraft engine-like conditions. The DNS results suggest that combustion increases the mean velocity of reactants, while the turbulence in the main swirling region and the shear layers is weakened. The recirculation in the center region is enhanced due to the stronger shearing. Analysis of the TKE balance equation demonstrates that the terms of convection, turbulent transport, and velocity-pressure gradient correlation play important roles in the current swirling flames with relatively high Karlovitz numbers, which is different from that of the planar jet flames. Compared to inert flows, the convection and turbulent transport terms in reactive flows are suppressed in the inner shear layer and enhanced in the main swirling region, while the velocity-pressure gradient correlation term changes little due to the weak pressure dilatation in the present configuration. The vorticity vector is preferentially aligning with intermediate principal strain rate in swirling flows, and this alignment is enhanced by flames in the low turbulent intensity case. When this preferential alignment works, dilatation term in reactive flows remarkably promotes the production of enstrophy. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.