Noise efficiency of fan designs

[MisterX]

In particular I am wondering about compressor blades, but it's an interesting question to pose for household type fans as well. We can imagine "waterwheel" type schemes, and also the more traditional schemes where the axis of rotation is parallel to the flow. Which produces more noise per airflow? Also are there consequences of the various designs in terms of overall output?

 

[russ_watters]

Typically, noise is a function of velocity. So to move the same amount of air with low velocity, use a larger fan and make it spin slower. Similar issue exists for generating pressure (generating pressure requires high velocity).