AnsweredAssumed Answered

propeller - weird forces explaining weird results

Question asked by Flegmatoid Zoid on Nov 9, 2016
Latest reply on Nov 9, 2016 by Bill McEachern

While doing a number of CFD simulations on variety of propellers, I've observed that:

- Solidworks results differ from theoretical (ideal) calculations by ~ 50%

- Solidworks results differ from real calculations by ~30%

 

I.e., 48" diameter (1.2m), 8.5" pitch (21cm), 2400RPM.

Theoretical maximum (Abbott f-la): 153N (or 17.2 kg) of Thrust.

By considering the propeller efficiency (70%-80%), expected results are in range from 107N to 122N

Solidworks gave 87N.

 

To further debug the problem, I've ran a force analysis on each of the propeller surfaces.

 

The results were rather surprising. The bottom surfaces seem to generate the opposite thrust of ~1/3 of upper surfaces' thrust.

My physics knowledge can't explain this.

 

By excluding these opposing (2x 25N) values, we would get ~138N.

That would be a fairly good estimate, because it would indicate a propeller efficiency of ~90%.

This is ok, because FEM cannot account for non-linear losses.

 

Are my assumptions reasonable?

Attachments

Outcomes