Just wanna share about this technology, I believe most EDF guys knows this principles already.

We knew that in EDF the head of stream is constant and also there's no added heat or thermodynamics. In order for the EDF to increase exhaust velocity like in turbine, we can change ducting diameter.

For reference here how it works. In EDF steady stream, there's no change in air density and volume flow rate is constant from inlet (intake) to outlet (exhaust).

The volume flow rate, Q

= Volume / time
= Area * distance / time
= Area * velocity
= (pi) * (radius)^2 * velocity
= (pi) * (Diameter/2)^2 * velocity
= (pi) * (1/4) * D^2 * v
= (3.14) * (0.25) * D^2 * v
= 0.785 * D^2 * v

Since Q is constant
Qin = Qout
we can eliminate constant value
Din^2 * vin = Dout^2 * vout

Now therefore,

EDF velocity / exhaust velocity = (exhaust diameter / EDF diameter)^2


Exhaust velocity can be expressed by:

Exhaust velocity = (EDF dia. / Exhaust dia.)^2 * EDF velocity