Tailoring the gain and phase of the flame transfer function through targeted convective-acoustic interference

This paper investigates how targeted interference between two well characterized sources of hydrodynamic disturbances can modify the response of premixed bluffbody stabilised H-2/CH4 flames with and without swirl. We introduce modulations into the Flame Transfer Function (FTF) through hydrodynamic interference between the shedding of vortices/wakes from different shaped bodies upstream of the flame and the vortex roll-up at the flame base caused by acoustic forcing. By placing a set of small diameter cylinders, a streamlined body, or a swirler upstream of the bluffbody and varying the distance from the dump plane, the gain and phase of the FTFs could be modulated at targeted frequencies providing a method to suppress thermoacoustic instabilities. We further investigate the flame response which shows that modulations in the fluctuating global heat release rate are caused by linear superposition along the flame front. At frequencies leading to destructive interference, large-scale wrinkling of the flame front occurs which increases the flame surface area but is offset by the simultaneous pinch-offof the flame tip which decreases flame surface area. Their combined effect reduces the amplitude of the fluctuating global heat release rate. At frequencies of constructive interference, large-scale wrinkling of the flame occurs before the flame tip pinches off, leading to an overall increase in the flame surface and amplitude of the fluctuating global heat release rate. (C) 2021 The Author(s). Published by Elsevier Inc. on behalf of The Combustion Institute.

Automated summary

This study investigates how targeted interference between two well-characterized sources of hydrodynamic disturbances can modify the response of premixed bluff-body stabilized H-2/CH4 flames with and without swirl. The Flame Transfer Function (FTF) can be modulated at targeted frequencies by placing different shaped bodies upstream of the flame and varying the distance from the dump plane. The flame response shows that modulations in the fluctuating global heat release rate are caused by linear superposition along the flame front, leading to changes in flame surface area and amplitude of the fluctuating global heat release rate.