Mj. Fisher et al., A MODELING OF THE NOISE FROM SIMPLE COAXIAL JETS, PART II - WITH HEATED PRIMARY FLOW, Journal of sound and vibration, 209(3), 1998, pp. 405-417
This paper reports the second part of a continuing study of the noise
of coaxial jets, and describes modifications to the model developed pr
eviously to allow for the effects of a heated flow from the primary no
zzle. The essential feature of the model described previously for the
prediction of the noise from isothermal coaxial jets was the identific
ation of three flow regions, within the coaxial jet flow, the noise pr
oduction of which could be estimated from single-jet prediction method
s. In particular, it was shown that noise from the principal interacti
on zone could be calculated by using single-jet prediction methods as
long as account was taken of the fact that measured turbulence levels
in this region were lower than those observed in a single isolated jet
at the same centerline velocity. For isothermal flows, for which only
quadrupole sources exist, allowance for this reduced turbulence level
was entirely straightforward. However, for heated flows both dipole a
nd quadrupole sources exist, and these have different dependencies on
the turbulence level. Hence to predict the noise one needs to know the
relative contributions of the dipole and quadrupole sources. In the p
resent work, use has been made of previously published results for the
se relative contributions, as a function of jet velocity and temperatu
re, for single jets. This then permits prediction of the noise from th
e interaction zone, which is subsequently combined with that from the
secondary jet shear layer and fully mixed flow region, as before: Comp
arison between data and prediction over a range of jet velocity, tempe
rature and angle of observation again show very acceptable agreement.
(C) 1998 Academic Press Limited.