Abstract Submitted
for the DFD12 Meeting of
The American Physical Society
The Sudden Onset of Acoustic Effects with Increasing Nozzle-
Chevron Length In a Mach 0.9 Jet
RYAN A. FONTAINE, Department of
Mechanical Science & Engineering, University of Illinois, JOANNA M. AUSTIN,
GREGORY S. ELLIOTT, Department of Aerospace Engineering, University of Illi-
nois, JONATHAN B. FREUND, Departments of Mechanical Science & Engineering
and Aerospace Engineering, University of Illinois — The addition of chevrons to the
exit of a jet has been found to reduce far-field noise, making it an effective passive
noise reduction technique. The selection of specific designs, however, is challeng-
ing since mechanics models provide insufficient guidance and computations remain
far too expensive for trial-and-error parameter exploration. To assess the design
optimization problem, we have experimentally evaluated parametric dependence of
sound on chevron geometry. Specifically, rapid prototyping is used to change the
model geometries and study the relationship between chevron length and the far-
field jet noise. We show that the effect of the chevron starts relatively abruptly
for lengths less than 4 mm, which is well less than the 16 mm length selected as a
starting point from previous studies. Thus a small increase in the chevron length
can produce a large change in the far-field sound. However, for longer chevrons the
sound is insensitive to the length, which has important implications for design op-
timization. Additionally, other flow diagnostics are performed to better understand
the flow characteristics resulting in the observed changes in jet noise.
Ryan A. Fontaine
Department of Mechanical Science & Engineering, University of Illinois
Date submitted: 02 Aug 2012
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