I hope this is the right place for this, if not, please feel free to move it elsewhere.
The question about the Me 309 wing profile in the book-review thread piqued my curiosity.
https://www.secretprojects.co.uk/th...itics-by-dan-sharp-and-calum-e-douglas.41814/
So I put together a small comparison done in XFOIL (viscous mode). The data for the unmodified NACA 15014 are taken from
Airfoiltools.com, just as the wing profiles of the P-51 D and H.
The modifications done to NACA 15014 in order to match the Me 309 airfoil designation which can be found in Dan's book, were done by me in XFOIL, I hope they are accurate. At least they look right. Thanks to Sienar for linking to the explanatory thead for reading german modifications to NACA profiles. Please also note the wonky quality of the P-51 D profile and pressure distribution resulting from the available profile-dataset.
For the comparison I chose Ma 0.5 since I wanted to steer clear of any transonic effects while being relevant to the speeds these planes flew at. Different Reynolds numbers are included, you might want to discard the Re 1,5000,000 results, since there seems to have been faulty user input causing some of them to run at 15,000,000 instead. I also limited the angle of attack range to maximum 6° since I wanted to avoid any separation issues.
The laminar to turbulent transition in these simulations was apparently triggered by a separation bubble (visible as a plateau in the total pressure distribution). Higher Reynolds numbers make this effect slowly disappear (as it should) so I feel relatively confident in the chosen Reynolds number range w.r.t. its capability to show the effect which I wanted to see.
What can you take from this?
The transition from laminar to turbulent flow indeed happens later for the Me 309 profile (so the modified NACA15014-0.825-37) compared to the unmodified NACA15014 (Re 1,000,000, AoA 0°, estimated 68% axial chord end of suction side transition bubble NACA15014-0.825-37 vs 51% axial chord end of suction side transition bubble NACA15014) . However, the P-51 H profile shows this only at roughly 76% axial chord. The P-51 D profile shows this phenomenon at 52% chord but since the surface is so wobbly this is most certainly not accurate and artificially shifted towards the leading edge.
Now can the NACA15014-0.825-37 be considered a laminar flow profile? Yes and no, I would say. It is more of a laminar flow profile than a typical NACA15014. But it does not reach the laminar flow lengths of the P-51 H profile. This is aggravated by the fact, that the Me 309 profile has a lower cl compared to the P-51 H Mustang profile at the same angle of attack and thus needs a higher AoA to generate the same lift as the latter profile. This in turn causes a forward shift in the transition point and shifts the scales even further in favor of the P-51 H profile. Just look at the large advantage in L/D the H Mustang profile has!
The attached document contains the plots on which I based my conclusions, please let me know if you think there is an error.