Cyclone separators use swirling flows to separate particles from air. This flow produces oscillations that manifest themselves as unwanted high-pitch noise in vacuum cleaners and result in structural damage in large industrial separators.
The oscillations can be thought of a wobbly spinning top. When the axis is vertical it spins smoothly but when the axis is off-vertical then the top wobbles about the axis.
Looking down with a high-speed camera into cyclone, we can see the wobbly flow
These oscillations make a high-pitched sound that we call a “cyclone hum”.
We have developed a new experimental technique to model and characterise the cyclone hum. Dyson are now using the technique to design the next generation of vacuum cleaners.
Characterisation of acoustically linked oscillations in cyclone separators. In: Journal of Fluid Mechanics, vol. 780, pp. 45–59, 2015, (15pp).