This investigation considers the effect of axial pressure gradient on the dynamics of flame-vortex interaction for a lean premixed bluff-body stabilized flame. Large eddy simulations (LES) of four different combustor geometries generated through combustor wall adjustments that resulted in mild to strong pressure gradients are studied. A bluff-body stabilized combustor for a propane/air flame is analyzed first. Results are compared with all available experimental data with the purpose of validating the LES methodology used in OpenFOAM and obtaining a base solution for the study of the pressure gradient effect on flame-vortex interaction. The role of the pressure gradient on flame structure, emission characteristics, vortex dynamics, and flame stability are presented.The mild favorable pressure gradient due to the decelerated flow in diffuser configurations influences flame-vortex dynamics by suppressing flame-induced vorticity sources; baroclinic torque and dilatation, and hence resulting in augmented hydrodynamic instabilities. The sustained hydrodynamic instabilities maintain the large flame wrinkles and sinusoidal flame mode in the wake region. The nourished near lean blowoff dynamics also affect the emission characteristics and the emission of species increases. However, the accelerated flow in the nozzle configuration amplifies the flame-induced vorticity sources that preserve the flame core hence resulting in a more organized, symmetric, and stable flame. Ultimately, the combustion performance and operation envelope in the lean premixed flames can be increased by maintaining the flame stability and suppressing the limiting lean blowoff dynamics and emissions with the help of a strong favorable pressure gradient generated through adjusting the combustor geometry.

This study presents numerical investigations of turbulent premixed bluff-body stabilized flame by emphasizing the influence of pressure gradient on flame-vortex interaction and flame stability for lean combustion applications. Large eddy simulations of four different geometrical configurations, diffuser 3°, diffuser 1.5°, nominal, and nozzle that resulted in mild to strong pressure gradients are presented. Numerical investigations allowed determining the effects of geometry-induced pressure gradient on the flame structure, development of the flame-front vorticity and turbulent structures and flame stabilization. It is shown that the pressure gradient plays a key role for the spatial and temporal development of the flame front vorticity and baroclinic torque. The flow deceleration in diffuser geometries suppresses the flame-induced vorticity mechanisms, which in turn lead to large wrinkle forms of the flame and may lead to local extinctions along the flame front. The favorable pressure gradient in the nozzle geometry, on the contrary, increases the baroclinic torque that restrains the development of the shear layer vorticity and hence prevents local extinctions.

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