To achieve jet noise reduction goals for the High Speed Civil
Transport aircraft, researchers have been investigating the mixer-ejector
nozzle concept. For this concept, a primary nozzle with multiple
chutes is surrounded by an ejector. The ejector mixes low-momentum
ambient air with the hot engine exhaust to reduce the jet velocity
and, hence, the jet noise. It is desirable to mix the two streams
as fast as possible in order to minimize the length and weight
of the ejector.
An earlier model of the mixer-ejector nozzle was tested extensively
in the Aerodynamic Research Laboratory (ARL) of GE Aircraft Engines
at Cincinnati, Ohio. While testing was continuing with later generations
of the nozzle, the earlier model was brought to the NASA Lewis
Research Center for relatively fundamental measurements. Goals
of the Lewis study were to obtain details of the flow field to
aid computational fluid dynamics (CFD) efforts and obtain a better
understanding of the flow mechanisms, as well as to experiment
with mixing enhancement devices, such as tabs. The measurements
were made in an open jet facility for cold (unheated) flow without
a surrounding coflowing stream. The photo shows the experimental
setup. Distributions of streamwise vorticity as well as turbulent
stresses were obtained using hot-wire anemometry for a low nozzle
pressure ratio. Pitot probe surveys were conducted for higher
nozzle pressure ratios.
The figure shows the mean velocity distribution inside the ejector.
The outline of the interior of the ejector is shown for reference.
The distribution exhibits a cellular pattern because of varying
velocities through the primary and secondary chutes. Corresponding
streamwise vorticity data show that pairs of counter-rotating
vortices originate from the chutes and persist over the entire
length of the ejector. The velocity distributions also reveal,
with increasing downstream distance, an interchanging of low-velocity
regions (marked with an
L
) with adjacent high-velocity
regions (marked with an
H
). This occurs because of the
action of the streamwise vortices as fluid is continually transported
laterally by the vortex pairs. Although the data shown are for
a low-pressure ratio, corresponding distributions at higher pressure
ratios exhibit a similar behavior, in some cases, with the interchanging
occurring more than once within the ejector.
Previous articleLast updated April 29, 1997
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