it was pouring rain all day yesterday, so I had the idea of putting the gopro on the back bumper to see what kind of water/mist patter was coming off the car. Just driving down the highway, there definitly seemed to be more spray/mist in the air than it normally would. Usually I don't see much of the spray up high in the rear view. Today however I saw A LOT of spray in the rear view, enough to cloud the car behind me pretty well!
Here is the video I took (shortened to just the highway part) from the rear bumper. Sadly between the rain drops on the lens and the faint/transparent-ness of the water/mist it is REALLY hard to see much of anything happening with the airflow. If you look carefully between rain drops there appears to be a faint "line" of water spray extending parallel with the diffuser outwards.
There also appears to be a lot of water falling off right at the leading edge of the diffuser. This could be airflow separation making the water fall off, or could be a function of the airflow changing in the diffuser and water being heavy... I'm not really sure what that means, and I doubt I'll ever really know. *shrug*
yarn test/video will be coming soon.