Characteristic Curve Differences Between AeroDyn and Tidal Bladed

Wind & Water Rotor Aerodynamics
1

Hi everyone,
I’m having some difficulty getting the characteristic curves between AeroDyn and Tidal Bladed to match up. They have the same blades, polars, inputs and similar axial induction, tangential induction, AoA and Reynolds Number across the span, yet the characteristic curves aren’t even close. I know that AD and TB use different Tip and Hub loss models so I tried turning those off and they still don’t match up. Does anyone know what could be causing this discrepancy?

CharCurve
CharCurve715×421 18.9 KB

Thanks,
Conor

2

BladeSpan
BladeSpan953×575 46 KB

NoLossCharCurve - Copy
NoLossCharCurve - Copy718×422 15.5 KB

NoLossBladeSpan
NoLossBladeSpan978×622 50.4 KB

3

Dear @Conor.McCune,

The axial and tangential induction, angle of attack, and Re # are quite close in your plots, other than at the root and tip, which surprises me that the resulting Cp is so different.

In your first plot of Cp vs TSR for different RPMs, I see 4 labels, but 3 plots. Are the two AeroDyn results on top of each other? I would expect that, unless structural deflection is considered. Could that be the cause of the differences–i.e., that structural deflection is considered in your Tidal Bladed results, but not in your AeroDyn results? I.e., are you using the standalone driver for AeroDyn rather than AeroDyn within OpenFAST?

It would also be helpful to compare the normal and tangential force per unit length between the two solutions.

Best regards,

4

Hi @Jason.Jonkman,
Thanks for getting back to me so quickly. I was running AeroDyn with a standalone driver. I did have mass properties included for Tidal Bladed but blade flexibility disabled. I then ran a simulation in TB with both blade mass and flexibility disabled and still saw a discrepancy between 12 and 24 RPM.

StructuralModesDisabled
StructuralModesDisabled1111×746 55.3 KB

I am using polars with multiple reynolds numbers but am not sure why AeroDyn doesn’t see a difference in Cp between different RPM but TB does?
Here’s what I found for the normal and tangential force relative to the chord.
NormalTan Force
NormalTan Force474×571 21.5 KB

I used Tidal Bladed’s Hydrodynamic Axes and took the negative of the y direction for tangential.
TB HydroAxes
TB HydroAxes690×624 75 KB

Thanks for the help,
Conor

5

Dear @Conor.McCune,

With the same airfoil data and a rigid rotor, I would expect the BEM solution to depend only on pitch and TSR, not on rotor speed. I’m not sure how much your airfoil data is changing between the different Reynold’s number to comment on what effect that may have.

Regarding the normal and tangential forces, the normal force from AeroDyn is definitely what I would expect to see–with a peak around 70% span. The tangential force is also what I expect, other the sign is backwards, but I guess this depends on what coordinate system you are using. The results from Tidal Bladed look odd to me, but perhaps you the Tidal Bladed output you are using is not the applied aerodynamic forces per unit length, but rather some reaction load in the blade. I would double check.

Best regards,