ABSTRACT
Environmental concerns have led to the development of combustors which burn
lean mixtures with consequently low NO
x
emissions. One limitation in ducted
ows stems from naturally occurring oscillations which can have amplitudes suf-
cient to do physical damage, and these may stem from acoustic coupling in a
range of equivalence ratios from 0.75 to 1.2 and from poor stabilization close
to the lean ammability limit. Longitudinal frequency modes dominated the
ows with frequencies of the order of 100 Hz [1{4] and generally gave rise to
combustor duct [5]. Ducts with exit nozzles sometimes gave rise to bulk mode
(Helmholz) frequencies which were associated with poor ame stabilization [6,
7]. These investigations were characterized by comparatively simple geometric
congurations and by heat release rates far below those of practical combustors.
