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Werner Lazeroms (TU/e)
| Speaker: |
Werner Lazeroms (TU/e)
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| Date: |
Wednesday December 8, 2010
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| Title: |
Sound
propagation in slowly varying lined ducts with temperature gradients
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Abstract
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The
design and production of aircraft engines is an expensive affair. One
important aspect is the emission of sound, which should fulfill all
kinds of regulations. Therefore, aircraft engine manufacturers would
like to effectively study and measure the amount of noise produced by
their engines. Both the construction of experimental prototypes and the
numerical simulation of the complete set of equations are extremely
costly, so good analytical models are of great importance. In this
presentation I will present some models of sound propagation in (slowly
varying) ducts, in the presence of mean flow and temperature gradients.
The problem is based on the specific configuration of sound propagation
in the so-called Auxiliary Power Unit (APU) at the back of an aircraft,
where large temperature gradients are typically prevailing. The models
make use of the WKB approximation to account for a description in terms
of modes, even in slowly varying ducts with a non-uniform wall
impedance. The main result is a very general expression that can be
used to determine the pressure ‘eigenfunctions’ in a cylindrical slowly
varying duct with general mean flow and mean temperature profiles.
Furthermore, the acoustic field was numerically simulated in order to
visualize the flow of acoustic energy and to evaluate the influence of
the mean flow and mean temperature on the damping of certain modes.
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