What you're getting at is the Kutta condition: https://physics.stackexchange.com/questions/135707/what-is-a-physically-accurate-explanation-for-the-kutta-condit

What you're getting at is the Kutta condition: https://physics.stackexchange.com/questions/135707/what-is-a-physically-accurate-explanation-for-the-kutta-condition https://physics.stackexchange.com/questions/135707/what-is-a.... This only arises in viscous flow and ensures that the upper and lower flows leave the trailing edge smoothly. Without this, the flow would not be turned.