I have a question regarding the production mechanism of induced drag.
I understand the downwash aft of the trailing edge (steaming from wingtip vortices) causes the induced drag by changing the relative flow (blue line) into the effective relative airflow (red line), and thus by bending the lift vector rearward (L to Leff).
My question here is: How does the downwash, that has already passed behind the trailing edge of the airfoil, influence the airflow upstream, causing the entire relative airflow to bend upward as in the picture.
Or is it just an imaginary concept to explain the induced drag?