Cp. Cadou et al., TRANSPORT ENHANCEMENT IN ACOUSTICALLY EXCITED CAVITY FLOWS, PART 2 - REACTIVE FLOW DIAGNOSTICS, AIAA journal, 36(9), 1998, pp. 1568-1574
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.