![](http://acoustics.eng.cam.ac.uk/wp-content/uploads/2016/11/handriers.jpg)
High speed hand driers, such as the ones made by Dyson, dry hands efficiently by ejecting a jet a a high speed – up to half the speed of sound. The jet comes out of the nozzle as laminar flow, mixes with the surrounding air, becomes turbulent and radiates noise.
![](http://acoustics.eng.cam.ac.uk/wp-content/uploads/2016/11/JetMixing.jpg)
The jet contains coherent structures that are efficient for sound radiation
![](http://acoustics.eng.cam.ac.uk/wp-content/uploads/2016/11/JetSchlieren.jpg)
Schlieren image from a thin rectangular jet
We are modelling the noise sources and finding ways to reduce the noise.