Insertion Loss of Spiral Ducts - Measurements and Computations

This work presents measured and computed characteristics
of insertion loss (IL) of spiral ducts. Numerical and experimental models of
spiral ducts have been investigated. For the numerical modeling, a three
dimensional model computed by the use of a finite element method in a COMSOL
Multiphysics computer application has been used. For the experimental modeling,
there has been made a spiral duct model by using a three dimensional rapid
prototyping technique. An acoustic system with a round silencer has been
ivestigated, and the spiral duct has been inserted at the inlet. IL is
considered in this paper as the difference between the sound pressure level
(SPL) [dB] probed at only one outlet point of the acoustic system without and
with an acoustical filter (spiral duct), respectively. The results of measured
and computed IL of spiral ducts presented in this paper confirm the fact that
this newly discovered technical solution for attenuating sound in ducted systems
has an applicable potential. There are visible small discrepancies between the
measurements and computations. The results can differ due to the non ideal
dimensions of the experimental model and the non ideal inlet and outlet
surroundings of the experimental acoustic system. However, the IL
characteristics of the computed model is almost wholly covered by the IL
characteristics of the measured model.