Said fan curves are measured, not calculated. Fan design is a black art!!

Bugs wrote:
I assume that you are talking about fan output curves. They correspond
to water pump output curves. It is simply a plot of the output pressure
vs. output volume for any given impeller/fan style. At zero flow with
the outlet blocked the pressure will be at a maximum. At maximum flow
with the outlet fully open, the pressure will be near zero. The curve
traced betweeen these points shows the operating point for any
condition of discharge resistance, ie. friction. Somewhere on the curve
is a point that requires the maximum horsepower for that particular
fan, which produces the most volume at the greatest pressure possible.
There is usually a horsepower curve associated with the discharge
curves which shows the motor HP required at any point on the curve.
These are used to select the proper fan motor/impeller/HP combination
for design of a system.
Bugs