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Old Nov 27, 2002, 02:57 PM
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P_J_Glor's Avatar
Valencia, CA
Joined Oct 2002
3,612 Posts
Inlet/fan/outlet ratios

I have seen a couple of "rules of thumb" on this site indicating the outlet or exhaust diameter should be 90% of the fan diameter in one case, or 80% of the fan diameter in another case.

The instructions with the Wattage Powerfan 400/6 EDF Unit says the exhaust and inlet should be equal to or greater than the fan diameter. Obviously, the outlet diameter may affect the choice of jets to model or at least the size of a model to have a reasonably scale-like exhaust with minimal cheating.

I have also seen the use of a tailcone aft of the fan to keep the cross-sectional area fairly constant from the fan to the exhaust.

I also gathered from some of the threads here that it may depend on the fan unit itself -- high rpm, high volume, high static...

So I guess my question is: What are the "rules of thumb" for inlet/fan/outlet diameters for 1) best performance; and 2) what I can get away with for scaling inlet/outlet sizes.

The particular fans I am interested in are the KP44, GWS EDF-50, and Wattage Powerfan 400/6 EDF.

I realize there are probably no simple answers, but your advice would be greatly appreciated. Thanks!

Pete G.
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Old Nov 27, 2002, 03:36 PM
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St. Mary, Maryland, United States
Joined Dec 1996
8,303 Posts
For those low power fans I would follow the instructions you have. You need some significant power and speed to work with in order to start restricting inlets and outlets.
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