Wind fences on half-bed cover?
 

As I have done my own research on aerodynamics, I have noticed that there is the counter-rotating vortices on each rear corner of a vehicle, that is, the rotation on one side is opposite the rotation on the other side. Having a pickup truck and interested in a half-bed cover, would there be any benefit to having a wind fence on each side of the bed? I am thinking this would help "straighten" out these vortices, and at least keep some air that is coming over the cab from "rolling" down over the edge of the bed toward the rear.

If so, what kind of dimensions and shape should they be? Yes, I have a secondary purpose of a wind fence in mind, but am curious as to whether wind fences would be beneficial and not a detriment. No, I am not thinking in terms of a raised "spoiler" across the bed as some trucks have been seen over the years.

My truck cab height is 20" above the bed rail at the corner, with the inside bed dimensions of 73" by 56".

Something like this?

http://graphics8.nytimes.com/package...T/22364449.JPG

Yes. I had envisioned something along the lines of the silver car's wind fences.

fences
 

I believe that counter-rotating vortices are most prominent with pseudo-Jaray/'fast-back' cars with too steep a backlight angle.
Your pickup should be suffering from a very large captured-vortex spinning perpendicular to your line of travel within the open bed.
You might be able to 'tailor' this vortex a bit by modifying the rail height and inclination but to diminish the vortex significantly you'll need to address both the back of the cab and where the 'floor' of the bed is.
Here at the aero forum there are a number of threads dealing with pickup drag reduction which speak directly to your problem.
Search around a bit and see if you don't find something which will help.

aerohead,
I take it you are referring to the horseshoe vortex that occurs behind the cab. So any effect a wind fence would have would be miniscule to the main problem of minimizing or eliminating the horseshoe vortex, right?

I did find out quite by accident how much air pressure is hitting the tailgate area and basically at least the last third of the bed "floor". I put a heavy steel weight in the back (in the center next to the tailgate) of my truck for better traction in snow. I put it in a good size but short (about 24" by 18" by 10" high) cardboard box inside a plastic bag to keep the box from getting wet. At 55 mph that plastic bag had pushed the flaps of the box (not very strong anyway) down into the box and the plastic bag looked like it was glued down into the box.

Hauling bags of garbage to the dump really shows how violent the wind gets back toward the tailgate but relatively calm up close to the cab. I tend to notice how the wind effects other objects that people are hauling in their truck.

horseshoe
 

Yep,the big dogs will tell us to go after that drunk tornado lying on it's side.
Since your actually hauling,the cab wing extension and half-tonneau might help 'cause it has mpg performance close to an aeroshell,but leaves most of the bed 'open' for the utility of it.

Been thinking along the same lines.
 

If you watch the aerolid flow visualization video closely you can see the tufts of yarn tend to split along the rear edge of the lid.

The yarn splits at center and the ones on the left point left and the ones on the right point right. This illustrates the two counter-rotating vortexs you speak of. What caught my attention was that the air stays attached pretty well along that lip.

Here is a scale model of a small electric car I did last year having vertical winds to control flow at the rear corners and behind the vehicle. The fins could be warped to optimum shapes for different speeds.

Bondo

photo
 

Brett,I did get a photo of that Cd 0.20 car I told you about and will mail soon.I'm behind on everything seems like.You all can call me Mr. Late!
Love your EV model!!!!!!!!!!!!!!!