# Issues with AeroDyn Standalone

Hi All,

I am currently testing the AeroDyn v15 Standalone version. I found something interesting with the results. Any help is greatly appreciated.

I did a series of tests on NREL 5MW blade with 10 rpm initial rotor speed and 10 mps steady uniform wind (zero precone, zero shearExp, zero yaw, and zero pitch). The dT is 0.03 sec with total Tmax 12.00 sec

Case 1: ShftTilt=0, yaw=0, Precone=0

• The azimuth angles DO NOT very with time-step. It is constant at their initial state (Blade 1 at 0 deg, Blade 2 at 120 deg, Blade 3 at -120 deg)
• Therefore, all the Vrel, Phi, Alpha (AoA), Cl and Cd are constants in this 12.0 sec simulation
Why the azimuth angles do not change with time? Does it mean the rotor is not rotating? Please advise.

Case 2: ShftTilt=20, yaw=0, Precone=0

• Blade 1 initial Azimuth angle starts at -90 deg.
• The azimuth angles now VARY with time-step, rotating CW. direction.
• all the Vrel, Phi, Alpha (AoA), Cl and Cd are NOT constant in this 12.0 sec simulation

Case 3: ShftTilt=-20, yaw=0, Precone=0

• Blade 1 initial Azimuth angle starts at 90 deg.
• The azimuth angles now VARY with time-step, rotating CW. direction.
• all the Vrel, Phi, Alpha (AoA), Cl and Cd are NOT constant in this 12.0 sec simulation

Based on the picture below, AoA of each blade should change in both Case 2 and Case 3

However, the AeroDyn results show that B1 AoA are the same for both Case 2 and Case 3 when the B1 is at azimuth angle = 0. The below picture show the B1 AoA at azimuth =0 and after one full rotation. All the line overlay on each other because they have the same value. Notes that the same thing happened for tilt =0, yaw=20 case.

Here are better pictures to understand the issues. The pictures show B1 AoA of a full revolution (azimuth angle starts from 0 to 360).

From my understanding, Case 2 is correct because AoA changes and its symmetrical to the vertical axis. Case 3 should have changes in the bottom area, but the AeroDyn result shows they are the same.

I have change dT, skewMod, and other parameter, but it still provide similar results. I do not understand what is going on here.

Here is the download link of my driver code, primary input code, and outputs of each case. The blade data is the same as NREL 5MW for its example.
Case 1: “T0_Y0.1.out”
Case 2: “T20_Y0.1.out”
Case 3: “T-20_Y0.1.out”
Case 4: “T0_Y20.1.out”
dropbox.com/sh/x474qykko60g … 5Jusa?dl=0

Any input or help is greatly appreciated. Thank you!

Dear Daniel,

Your questions seem to be related to the questions about AeroDyn’s blade-azimuth angle outputs that we discussed in a separate forum topic: http://forums.nrel.gov/t/azimuth-angle-of-the-blade/1464/1.

Again, AeroDyn’s blade-azimuth angle is defined relative to the inflow-skew angle. In Case 1, there is no inflow-skew angle, so the azimuth angle is undefined (and simply output as zero by AeroDyn). In Case 2, z_disk points to the right when looking downwind and so an azimuth of zero means that blade is pointing to the right. In Case 3, z_disk points to the left when looking downwind and so an azimuth angle of zero means that blade is pointing to the left. Your results seem consistent with this azimuth convention.

Best regards,

Dear Jason,

Thank you so much for the explanation. Just few questions:

1. How to know the z_disk points to right or left?

Case 2: Blade 1 with azimuth angle at -90 deg will point upward.
Case 3: Blade 1 with azimuth angle at 90 deg will point upward as well.
Please see the picture to check if my understanding is correct.

If this is correct, I still have the same AoA for both cases (Blade 1 are both in the vertical direction)

For Case 2, at Time = 6.00 sec, B1_Azimuth = -90,

Case 2 nodal AoA= [ 67.2021, 6.368361, 4.795432, 4.504047, 4.931961, 4.988134, 5.106888, 4.973749, -0.08621766]

For Case 3, at Time = 6.00 sec, B1_Azimuth = 90

Case 3 nodal AoA= [ 67.20213, 6.368365, 4.795431, 4.50405, 4.931962, 4.988136, 5.106889, 4.973748, -0.08621766]

For both case, the AoA are identical, even thought Case 3 have tilt = -20 deg. Is this correct result? Or it is my interpretation is wrong?

If I am wrong, how to I compare Blade 1 AoA at the same position?

Thank you.

Dear Daniel,

I described how x_disk, y_disk, and z_disk are defined in my posted dated Sep 29, 2016 in the forum topic linked above: http://forums.nrel.gov/t/azimuth-angle-of-the-blade/1464/1.

Yes, I agree that a blade pointing up will have an AeroDyn azimuth angle of -90deg for Case 2 and 90deg for Case 3. Without the Pitt and Peters skewed-wake correction enabled (SkewMod = 1), I would expect the AoA to be the same for this blade orientation because the streamwise (axial) component of the blade velocity is zero. When the skewed-wake correction is enabled (SkewMod = 2), there is a correction to the induction at this blade orientation and the AoAs would then be effected.

I hope that helps.

Best regards,