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Compressibility is only relevant in aircraft once they start getting near the speed of sound.



How about ground effect for helicopters (or hovercraft)?


Works just the same underwater. (Inviscid, incompressible). Low Mach number means compressibility is not significant. High Reynolds number means viscosity is not significant. Same for other dimensionless numbers and physical phenomena (Froude number etc).

Though note: compressibility is not the same as "exerting pressure". A hydrofoil or marine propeller works on pressure differences, even though the fluid is effectively incompressible.




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