TRANSPORT ENHANCEMENT IN ACOUSTICALLY EXCITED CAVITY FLOWS, PART 2 - REACTIVE FLOW DIAGNOSTICS

Planar laser-induced fluorescence is used to study the unsteady temper ature field associated with reactive flows in a two-dimensional dump c ombustor. These studies ape performed alternately under steady, natura lly resonant, and externally driven conditions. Fluorescence from an i nert seed (nitric oxide) is used to determine the temperature field. I mages of the temperature field taken under naturally resonant acoustic al conditions show evidence of strong perturbations of the flame, simi lar to perturbations seen in images taken during on-resonance, externa lly forced conditions. If the device is externally forced at the same amplitude hut at an arbitrary (off-resonance) frequency, however, the temperature field remains unperturbed, very nearly as if there were no acoustic excitation at all. Hence, the reactive cavity flow appeared to be preferentially responsive to external acoustic forcing at freque ncies at which the flow could potentially resonate anyway, given a suf ficient level of energy input by the reaction. External acoustical for cing using the loudspeaker provided such energy input at the specific resonant modes, resulting in increased thermal transport within the ca vity.