ADsk: correction to disk average velocity equations

[andrew-platt]

Merge after 3.5.5 cross merge (rebase then).

Feature or improvement description
AeroDisk calculations were using an incorrect set of points for the DiskAvgVel calculations. The set of points used in the previous calculation was aligned with the hub axis instead of perpendicular to the hub axis.

Related issue, if one exists
See PR #2532 for details

Impacted areas of the software
AeroDisk only

Additional supporting information
Merge this after cross-merging main into dev after the 3.5.5 release.

Test results, if applicable
Test results will change slightly with this change.

• r-test merge required

[andrew-platt]

Some regression tests with OpenFAST changed significantly:

5MW_Land_DLL_WTurb_ADsk

Figure1: Disk average wind velocity has changed significantly as the sampling area is now in the rotor disk plane. This gives slightly lower, but smoother, average wind speeds than when the disk averaging points were located in the wrong plane (circle lying in the rotating hub X-Y plane, so it was spinning like a circular egg beater in front of the rotor which gave the periodic spikes).

Figure 2: blade pitch changes as rotor loads change. The new results track slightly better than the original.

Figure 3: GenPwr comparison with 5MW_Land_DLL_WTurb case. This is closer to the expected full OpenFAST simulation with AeroDyn.

5MW_Land_DLL_WTurb_ADsk_SED

Figure 1: Disk average wind speed changes, similar to above case

Figure 2: GenPwr is closer to the full OpenFAST simulation with AeroDyn than before.

TSinflowADskSED

Similar differences were noted on the second turbine in this case (only the main FAST.Farm.out file is compared). The wake calculations are not as affected by the change in the disk average wind calculations.

Figure 1: Slight changes are noted in the wind velocity at the second rotor (note this is at the FF timestep).