The best explanation I have found so far comes from the "principles of flight" book from oxford (studying material for the EASA ATPL)
Basically as you encounter high mach numbers, air molecules ahead of the wing are given less notice about the in incoming airfoil. At low speeds there is plenty of time for the molecules ahead to upwash ahead of the leading edge. At high speeds this up wash occrus much closer to the wing and the upwash motion is "compressed". End result is that the air meets the wing at a steeper angle. This is cited as the main reason for the change in CL max with mach.
Compressibility effects start to become evident above 0.4 M.
L/D max also decreases at HIGH Mach
Last edited by RBF; 21st Apr 2022 at 12:45.