Acoustic attenuation performance of a round silencer with the spiral duct at the inlet

The acoustic attenuation performance of a round silencer with the spiral duct at the inlet
is investigated. A Finite Element Method was used for a three-dimensional numerical computations
in a COMSOL Multiphysics application. A time-harmonic analysis without airflow
was used for a frequency range from 10 Hz to 2 kHz. The results show that the spiral duct
at the inlet can improve the acoustic attenuation performance of a round silencer. The sound
attenuation depends on a spiral lead, an absorbing material and frequency. The transmission
loss of investigated acoustic system with spiral ducts is related to an initial acoustic system
with circular pipe. The results are shown as a growth of transmission loss $\Delta$TL given by
an insertion of the spiral ducts. A specific parameter given by relation of the spiral lead $s$ to
constant circular duct diameter d is presented as $s/d$ ratio. The value of $\Delta$TL is determined
by $s/d$ ratio and increases in specific frequencies. An acoustic wave, in those frequencies, is
there divided at the outlet of the spiral duct and major acoustic energy goes aside, directly to
an absorptive material, and minor acoustic energy goes axially to the silencers outlet. This is
the damping effect of the spiral ducts.