I am currently working on the Kline-Fogleman airfoil for NACA 23015 variant at Reynolds number 208800 with the configuration of the backward facing step of 50% thickness at 50% chord on the bottom surface of the airfoil. The KF airfoil gives higher L/D ratios for all pre-stall AOA and it also stalls at a slighty higher angle than conventional variant of the same series. The highest L/D value from Ansys Fluent was 22.45 at 9deg AOA as compared to conventional NACA 23015 at 9deg AOA being 19.74. I want to know if the KF variant of this airfoil profile can be used in turbine blades of a gas turbine engine and if it will produce higher power output or efficiency. Will it cause any problems due to turbulence and the number of blades and stages?

Also, are there any other applications of KF airfoils other than RC planes?


1 Answer 1


KF airfoils result from folding paper airplanes. In a way, most paper airplanes employ an airfoil with a stepped contour. At the scale of paper airplanes, this step possibly forces a laminar-turbulent boundary transition which might allow the airfoil to stall at a higher angle of attack.

A regular NACA 23015 has an optimum L/D of close to 50 at a Reynolds number of 200,000 and 9° angle of attack. Airfoiltools gives it as 48.5.

If you doubt the XFOIL data from Airfoiltools, NACA TR 824 gives essentially the same values using wind tunnel data, however, you need to pick Airfoiltool data at a higher Reynolds number to compare the two.

Since the L/D of the conventional airfoil is two an a half times better than what you calculated with ANSYS, I recommend that you review your results. And no, I would not recommend their use in turbines. The exposed corner at the step will face extreme heat loads and film cooling will probably fail there.


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