Use unstructured lift/drag interpolators

[eyoung55]

Purpose

This is a small PR to enable unstructured airfoil polar data to be used to define the lift/drag lookup tables.

Changes

The nrel_5mw airfoil polars are defined with different angular resolutions at different stations along the blade (e.g., station 0 has 3 aoa points, station 4 has 136 aoa points, station 7 143, and so on). The current approach to defining lift/drag lookup tables assumes a common angle-of-attack grid and makes use of a structured interpolation. To handle cases like the nrel_5mw the following changes have been made:

1. Use LinearNDInterpolator instead of RectBivariateSpline and refactoring to construct the right inputs for the former.
2. Update the truth values to reflect the slight changes brought about by the modified coefficients of lift and drag.

Additionally, some minor changes were made along the lines of enabling the nrel_5mw runs and verification:

1. Add a tip_loss option to enable turning off the tip loss model from the yaml file and rename value to tip_loss_fac to avoid confusion.
2. Save the axial velocity (normal to the rotor plane) as part of the along-blade data output.
3. Add log print statements for hmin, gaussian_width, and num_blade_segments.

Type of Change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update
• Maintenance update
• Other (please describe)

Checklist

• I have run existing tests which pass locally with my changes
• I have added new tests or examples that prove my fix is effective or that my feature works
• I have added necessary documentation

[johnjasa]

Looking great, this will be quite helpful for the V&V work!