Investigation into the Sound Power Level Reduction Achieved using Acoustic Jackets on a Centrifugal Fan and an Axial Fan

C1b - Noise Control by Passive Means

A very common method to reduce the noise radiated from a fan is to wrap the impeller casing with an acoustic jacket. This project seeks to measure how much an acoustic jacket reduces the noise from a typical fan and whether there are any opportunities for improvement. As part of the testing, axial and centrifugal fan configurations were used. The acoustic jacket material that was used was made from vinyl faced acoustic quilting and a 5kgm-2 barrier layer.

The A-weighted sound power level was measured using sound intensity measurements across a measurement surface encompassing the impeller casing, motor and a section of the inlet and outlet duct work. The measurements were also broken down in to the third octave frequency bands. The sound intensity measurements allowed for the generation of noise maps of noise radiating from the source.

The jackets were found to perform well on the axial fan as it was straight forward to enclose the noise source but for the centrifugal fan (3kW direct drive) it became apparent that the cooling fan on the motor was a key source. An acoustic jacket was developed to extend across the motor but not impede its performance in cooling air. This resulted in a reduction of the sound power radiated from the source down to the level of the break out noise from the ducting.

The noise mapping from the sound intensity measurements provided data in a visual format which demonstrated the relative importance of the different elements of the noise source including; scroll casing, motor and connecting ductwork which was important in developing the product. The main aim of this project was to produce data on the sound power level reductions that can be achieved using acoustic jackets on typical fan set-ups that would be found in the field.