Effects of covering portion of an axial fan blade? 2

[MechEng92]

In a scenario an axial fan is positioned on the top of a box drawing air in from three of the four vertical faces. A portion, lets say a fifth, of the fan blade is covered by some metal on the bottom of the fan closest to the middle of the three face openings. Will this effect the airflow through this open face much?

Please see crudely drawn MS Paint image attached.

 

[MFJewell]

The only thing I can think of is that it may be there to lengthen the path the flow has to take from that face. It would then draw air more evenly from all three faces.

 

[willard3]

You could also pre-rotate the airstream which would effect fan performance.

 

[DrRTU]

Don’t do it. 10 years ago we applied numerous 60” 70,000 cfm cast axial upblast fans in a large Sony warehouse. Sections of the warehouse had bar joists on 52”centers. Fans were on 11” curbs with butterfly dampers on outlet. Thus the fan had a 6” bar joist obstructing one side of the inlet. After 6 months of operation, numerous blades failed. Parts of the blades were found on the warehouse floor. Failures were at 6” in from the tip and at the hub. The mfg inspected the failures and the application. Based upon metallurgical inspections, the blade to found to flex up and down due to loading / unloading during a revolution. We changed to a steel blade with less flow and slower rpm. Lucky no damage was done to people or equipment.
Fans require even flow to load the wheel or blade evenly. Look at old style IGVs on cent. fans, the vortex damper allows to even out the flow.

 

[LittleInch]

DRRTU. Great advice.

The law of unexpected consequences....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[SAK9]

The impact on fan performance is dependent on how close the obstruction is to fan suction.This kind of system effect is impossible to calculate so have some margin for air flow.One way of reducing the influence of obstruction is to guide the flow around the obstruction using an eye shaped enclosure around the obstruction( some details are available in the Carrier handbook.

 

[RossABQ]

AMCA has some excellent materials on system effects, for instance:

https://youtu.be/PU_kLyamADY

Much more in their papers.