noise reduction

[pleaback]

The noise level of the cantilever fans is encouraging compared to axial fans. Keeping the fan frequency in the infrasonic region meant that the audible noise emanating from the fan is solely due to the aeroacoustics turbulence. Fans using 0.1mm thick steel were practically inaudible. However, the higher speed 0.5mm thick fans had noticeable noise (figure reported in the paper).

A cursory inspection of aero-acoustic theory suggests that the trailing edge of aerofoils are a major contributor to their noise. I did notice a measurable reduction of noise when I placed shrouds within 0.5 mm of the top and bottom edges of the fan blades. Reducing the noise from the fan tip edge eluded my admittedly short investigation. I had a few fan blades cut with different sized trailing edge chevrons and also tried placing fury material on the fan tip (a nod to owl wings).

The chevron geometries I tried had no noticeable effect. The fury trailing edge did reduce the noise produced, but also reduced the net flow rate.

As noise reduction of cantilever has not needed investigating in the past, I am optimistic that progress can be made in this area.