Turbines certainly do produce turbulence. I believe it takes around 10 blade diameters downwind for the freestream windspeed to recover, so the turbulence caused would probably extend a similar distance.
I totally agree. A short time ago we were approaching AMS over Flevoland (to the East of PAM) where each "new" farm appears to have it's own turbine. The whole of Flevoland was covered in dense but shallow fog and we could plainly see the wind turbines poking through the top. What was interesting was that each turbine not only disturbed the air directly downwind but the entire downwind quadrant. The distance affected appeared to be approx. 10 blade diameters. How much the air was disturbed I don't know, but you could clearly see the effect of the turbines on the fog and by implication, the surrounding air.
PM