ESDU 00024:2011

ESDU 00024 introduces a computerised method for estimating the
sound power attenuation of absorbent linings in constant section
straight rectangular ducts with axial flow. The method is based on
a theoretical model that takes the velocity profile across the
duct, assumed constant axially, into consideration. The method can
also be applied to annular ducts with inner radius to outer radius
ratios as low as 0.5, below which the risk of error increases. Up
to ten duct sections with different linings in each can be
considered. The program, ESDUpac A0024, permits the user to output
results at third-octave band centre frequencies, at specified
frequencies, or over a frequency range with constant step increment
between the frequencies. Equal energy in each mode or equal
amplitude in each mode can be selected. Individual modes can be
weighted. The output can be total attenuation at each frequency, or
the total attenuation and the attenuation in each mode at each
frequency. The format of the input file is explained and a second
ESDUpac, B0024, facilitates its construction. The input requires
values for the normalised acoustic impedance for each lined section
and, for low Mach numbers, values may be taken from ESDU 74003 and
74004, while for higher Mach numbers, the manufacturer's values
will need to be used. Worked examples illustrate the various
features of the program.

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