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?

If you want to "debug" the force calculation results, you need to take a look at the pressure profiles, since that's how the software calculates the forces. I guess the only way to judge the results would be to compare the CFD data to some experimental smoke visualizations or PIV analysis.