Computational and Experimental Investigations of a Sound Pressure Level Distribution at the Outlet of the Spiral Duct

This paper describes a computational and experimental investigations of a sound pressure
level distribution at the outlet of the spiral duct. A finite element method was used to
compute a three-dimensional numerical models in a COMSOL Multiphysics computer application.
Both, numerical and experimental models of the spiral duct were placed solidly in
a circular duct and they were approximately of the same size with a mandrel placed axially.
For experimental investigations of sound pressure distribution, the measurements were carried
out in a square plane, about 16 cm per 16 cm, perpendicular to the mandrel’s axis and placed
at a distance of 2.5 cm from the outlet of the spiral duct. The nearest surroundings of the
outlet of the spiral duct was covered by an absorptive material. As the computational outlet
surroundings was set up an empty air volume with a boundary conditions of a characteristic
impedance of the air. This gives the same conditions as an anechoic chamber. It is presented
that computational model is very similar to experimental one. Specific sound pressure level
distribution at the outlet of the spiral duct is presented as computed and measured experimentally.
This comparison shows good agreement between experimental and numerical results
and it reveals great potential for applications as a newly discovered acoustic band stop filter –
the spiral duct.