Qualify what high solidity means

[petebachant]

TODO

• Revise definition on line 46 (\pi D) in parentheses.
• Define with the c/R also and explain how this creates the flow curvature problem.
• Citation for lambda decreasing with solidity (Templin).
• What is high and low solidity? Fiedler and Tullis say 0.1 threshold, but we could use Migliore and define some delta alpha threshold