SUPPRESSION OF FLAME WRINKLING BY BUOYANCY - THE BAROCLINIC STABILIZATION MECHANISM

Buoyancy forces are known to alter the burning velocity of a turbulent flame by modifying the flame wrinkling process. To quantify how dame wrinkles are amplified or attenuated by buoyancy, a repeatable wrinkle of known size and amplitude is created in a premixed dame by interact ing the dame with a vortex. Images of the wrinkle amplitude were obtai ned for microgravity conditions in the NASA Lewis Research Center 2.2- s drop tower and for l-g conditions. Both thermodiffusively stable and unstable cases were considered. Results quantify the degree to which buoyancy suppresses the flame wrinkling; where buoyancy is removed, th e microgravity flames have a wrinkle amplitude that is 2-3 times great er than 1-g flames. Flame stretch effects also are observed because th e diffusionally unstable flames have larger wrinkle amplitudes than th e stable cases. The particle imaging velocimetry velocity data show th at two stabilizing mechanisms occur due to buoyancy: the conventional Rayleigh-Taylor mechanism and a baroclinic stabilization mechanism, wh ich has not been observed previously in combustion processes, Measurem ents show that the flame generates new vorticity, and this flame-gener ated vorticity can help to suppress the flame wrinkling.