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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?

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I don't think this graph is supposed to be very quantitative, otherwise there would be a "real" scale on both axes instead of the two-ended arrows and the hatched lines would be actual curves supported by some data points for specific airfoils.

What he's saying is that for a given airfoil thickness (constant y), the critical Mach number could be improved from one decade to the next, allowing faster flights without the drag penalty of transsonic flow. Or, for a given critical Mach number (constant x), the airfoil could be thicker, so the wing could be lighter or longer and more aerodynamically efficient. Or a combination of the two.

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  • $\begingroup$ Yup, I guess I was just wondering what changed about the underlying airfoil or sets of airfoils to allow that improvement from one decade to the next. He mentions the specific underlying CFD methods that allowed for the "jump" from one line to the next, but not what the output of those methods were. For example, I was hoping for a sentence like: "because of the use of 2D viscous solvers, we learned that varying the t/c ratio across span in XYZ pattern led to less drag penalty" or something like that. $\endgroup$
    – interested22
    Jun 6, 2022 at 22:02

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