I want to design a custom 3D printed fan that would be made of several axial fans that would be connected (fixed) to their cylindrical casing. I am planning to rotate the whole assembly (the cylinder with fixed - nonrotating fans inside) using one engine on one axle only around it’s axis. I am hoping to achieve a higher static pressure (sum of individual static pressures of fans). Do you think this will work?

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    $\begingroup$ Can you provide a diagram? "higher static pressure" than what? The individual fans, sure. A larger fan? Maybe not... $\endgroup$ Jul 6, 2018 at 18:12
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    $\begingroup$ This won't work well unless you design the second fan to deal with the outlet flow velocity from the first fan (which will have a tangential component). If all the fans run at the same speed, it won't work well unless there are static vanes in between the fans to straighten out the air flow. Look at multi-stage compressors in jet engines. You can do without static vanes if alternate fans rotate in opposite directions, but that doesn't seem possible with your design idea. $\endgroup$
    – alephzero
    Jul 6, 2018 at 18:34

2 Answers 2


The fan blades ideally should work like a wing getting lift (or giving lift, like a helicopter) out of 'flying' in a smooth stream or wind, not in a turbulent flow already agitated by previous layers.

So by adding more fans and turning the cylinder you may end up wasting the torque energy by just mostly twisting and turning the entire volume of air inside the cylinder with the blades, not producing much lift.

If you compare the old windmill fabric sales to the new wind-energy propellers you see the difference. The old design worked based on direct wind pressure on the sails, like a parachute. But the new blades act like a wing in the stream of wind, creating much more energy efficiently.

It is possible to create a lot of speed and pressure in an enclosed multi-layered turbine, but that has its walls purposely stationary, has vanes and gears, and the chamber itself narrows along as air accelerates.


I think this wouldn't work because of the following:

1- the amount of power needed to rotate the whole mechanism is going to be much more than the required power to drive each fan individually due to the added weight of the cylinder ( casing ).

2- the eccentricity ( offset ) between the casing axial axis and one of your fans axis, will cause that fan to work inefficiently due to that that the required time to complete one revolution per fan is going to be longer, thus less output power from fan since power = torque x omega ( rotational speed ).

3- also fan blade design will no longer be effective because the change in the blade angle of attack and other specs.

Consider using the total lost power to drive the fan on their own axis, I think you will get a better results rather than as expected.


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