I found this image in a paper titled, "Design and validation of advanced transonic wings using CFD and very high Reynolds number wind tunnel testing" that was published in part by Mark I. Goldhammer, the former Chief Aerodynamicist for the Boeing 777 project. In it he describes the evolution of wing sections over 4 decades. He notes the core CFD tools used to design each "generation" of wing, including:
- NACA empirically-derived sections for the 1960s generation
- Subsonic panel methods for the 1970s generation (in which he includes early widebodies)
- 2D Transonic Viscous Methods for the early 1980s generation
- "Early 3D transonic methods..primarily small disturbance methods that lack reliable viscous modeling" for the late 1980s generation
However, I struggle to understand what this graph is really depicting. While I understand that each iterative CFD method mentioned above is "advancing" the airfoil in some way, it's not clear to me in what way the airfoil is more advanced and how that is represented in the airfoil geometry (either of a single section or a set of airfoil sections). Would anyone be able to help decipher this graph?