"Struts" in propeller airflow 3

[amorrison]

I am designing a propeller support system (think wind tunnel) where the propeller shaft is supported by multiple radial struts that are very close(upstream and downstream)to the propeller. Propeller diameter 8.5 ft(2.6m), struts are 1.5 ft(0.5 m) upstream and 3 inches (0.1m ) downstream.
Propeller power will be 50 hp max. (37kW).

If there is equal angle strut displacement - resonance may be a problem. Maybe the strut regular displacement should be staggered to decrease the probability of resonance?

Any thoughts on the axial and tangential pulse forces on the propeller.

 

[MikeHalloran]

You should know the design speed range of the propeller, so you can design the struts to resonate outside that range. Additionally, you can space them unevenly, and make them roughly tangential to the shaft housing, not strictly radial, to diffuse the interaction between blade and strut. Maybe you can find some literature on the evolution of muffin fans, which have evolved considerably for acoustic reasons.





Mike Halloran
Pembroke Pines, FL, USA

 

[Sparweb]

The tangential mounting of the stator blades to the hub can be seen here:

There's obviously 1 less stator blade than propeller blades.


Steven Fahey, CET

 

[GregLocock]

Another trick is to vary the spacing between the blades so that they do not generate tonals. This is commonly seen on automotive cooling fans, but is generally applicable.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[plasgears]

This is a common problem in jet engine work. You have structures with even spacing struts with rotating fans/blades intereacting with passing freqs. Rotor-stator intereaction is another challenge. Vibration analysis over the range of operation is the key. Passing thru resonance on the way up to operating conditions is sometimes allowed.

 

[WKTaylor]

amorrison4 ... ref Sparweb's comments and photo...

Not only are the #of blades and struts unequal [odd-VS-even]... but the struts are canted "off the center axis" of the fan... while the fan-blades are roughly "on-axis". This is useful for improved torque stiffness... and misaligns the strut and blade axis(s)... for improved vibration resistance.

Regards, Wil Taylor