This paper describes an experimental characterization of the phase drift ch
aracteristics of the oscillating pressure in an unstable combustor. It is s
hown that the phase continuously drifts in a predominantly irregular manner
and, given enough cycles, substantially drifts from its "initial" value. I
t is also shown that the mean-squared value of the phase drift monotonicall
y increases with the number of cycles, a result that is consistent with the
predictions of a random walk model. It is concluded that these phase drift
characteristics are primarily caused by random processes (i.e., noise) and
, thus, do not reflect the underlying low-dimensional dynamics of the insta
bility. (C) 2001 Academic Press.