An obstruction can create turbulence for a considerable distance. Measurements of windbreaks showed reductions in windspeeds (where H is the height of the obstruction): at 10H range 66% reduction; 20H - 14% reduction; 25H - 10% reduction.
Effects were measurable up to 30H downwind (4%)
With a wind turbine it is not just the height that is important - the actual obstruction size is the rotor diameter (D)
Turbulence is usually regarded as significant 2D in front of the rotor, 2D above the rotor and 10D downwind.
Turbines are rarely placed less than 6D apart. This more due to the loss of turbines through turbulence than loss of power on the occasions when they are directly downwind. The blades are wings - in severe turbulence they flex - and in a number of cases they have hit the pylon! - Hence 6D seperation!
The East Midlands turbines are going to be interesting.... but it must be remembered that they are rather small (only 27m diameter) compared to the latest turbines being constructed. I believe they are 3-400m to the side of the runway so unlikely to have a major turbulence problem (for aviation!)