Response of an acoustically forced flame to vortex shedding of a circular cylinder

Understanding the characteristics of structures arising from vortex shedding can be of great importance in combustors, where controlling thermoacoustic instabilities is primarily desired. An experimental study is conducted on the interaction of a circular cylinder with an oscillating flow and the subsequent response of a bluff body stabilised CH₄/H₂ flame to such form of acoustic forcing. The flow has a non-zero mean velocity, ¯u of 10 m/s at the exit with forcing frequency ranging from 0.05 − 1 kHz and forcing amplitude maintained at 5 % of ¯u. Measurements of the flow and flame properties were carried out through hot-wire anemometry and planar particle image velocimetry (PIV), and by photomultiplier tubes and high-speed imaging capturing OH*-chemiluminescence, respectively. The findings confirm the classical case of vortex lock-on of the upstream cylinder and reveal that the flame reacts correspondingly as the heat release rate also locks onto the sub-harmonic, akin to the vortex shedding. These results highlight the potential in controlling the onset of thermoacoustic instabilities through the effect of acoustic/convective interference between vortex shedding behind cylinders and acoustic forcing of a bluff body stabilised flame.