How LE flaps make air fighter looks different in high maneuver

First, let me ask you a question. Do you think F15 haves a vortex lift? No matter what Quora said, any wings with that AR will have a strong vortex lift.

Here is a simple way to prove that. With some papers, you can easily get Cl of F15 as a ruff number.

Cl of F15 is around 0.96 at 20 degree alpha, and real Clmax is gonna be way higher than that. But the F15 airfoil’s 2d Clmax is only around 0.6(re=90000000, NACA 64A005). Which means actually F15 doubling lift by vortex lift.

Here back to today’s topic. I made two models of aircraft, and the only difference is one haves leading edge flaps and another don’t. But after CFD, it gives quite interesting results.

While aircraft in maneuver make low pressure area above. When air comes through, it will be cooling down and water vapor will condense into water droplets which is clouds. So it is a story about how pressure distributes on aircraft.

By comparing two models in different alpha. Here is some clue:

While in lower alpha, LE flaps make airfoil have more chamber and more lift. So naturally makes models with LE flaps have lower pressure. But in higher alpha, LE Flaps appear to reinforce Vortex generated by LERX. Also, lower pressure makes it more visible as clouds.

Back to F15. F15 doesn’t have LE flaps, and while alpha increases it is not that much easy to see its wing root generate clouds. On the other hand, F22 looks quite similar while lower alpha but clouds easily covers wing roots and even inlet in high alpha. it may have some relationship after all F15 and F22 have a lot of different.