Originally Posted by
JKEpps
Question, why does an inlet ring make that much difference? What about if you're using an inlet duct? Should you still use an inlet ring, and bring the duct up to the outside diameter of the ring? Thanks!
-Jorden
If you run a fan on the bench with a sharp edged housing lip you will have a huge amount of turbulence around the intake edge and the fan will starve of air, rpm increases as the fan is unloaded and the result is lower thrust and can be easily 30% down on smaller fans, with my 127mm fan I see around 15% drop on the bench. So most fan builders try to test with rounded lips at the front to smoothen the air out, you can hear a huge difference between a smooth inlet and a sharp one.
Inside your model its a different scenario, as your inlet ducting creates the smooth flow path to the fan, you want the ducting as clean and neat as possible right up to the fan and you want the intake lip at the entrance to the duct or ducts, IE the intakes should be rounded to obtain a smooth flow into the ducting.