Aerodynamics of Open Big Rig Trailer Door
 

On my way home from work tonight, I was getting on the freeway and had to merge behind a big rig. Nothing special except that the trailer door of the big rig was wide open (it was one of those roll up doors, not the two swinging doors). It got me to thinking what the aerodynamics of having the open (or even half open) door is. Does anybody know what will happen with the door open or can somebody do a quick simulation in Fluidworks or something? Will it cause more eddy currents to be created inside the trailer, thus increasing drag?

Thanks!

open
 

In past reporting it was aid that separation vorticity can cause a collision normal to an aftbody truncation,imparting a small degree of forward thrust.Some Corvettes were designed with this in mind.
With an opening,there is no surface available for which this impact to impinge and the kinetic energy is lost to viscous attrition within the box cavity.

I'm sorry, I'm one of those guys that knows just enough to get myself in trouble (which seems to have happened here :)). Can you put that in layman's terms for me. So is it a good idea (aerodynamically) to have the door open? I'm lost...

terms
 

Without knowing more than I do,I'd recommend closed doors.
One of our members in Europe tested his streamlined Nissan pickup,with open and close rear bulkheads and reported better effect with the closed off configuration.
A neighbor which ran a boat tail/ box-cavity on his VW Vanagon saw only limited benefit with the open rear although he was delighted to have extra storage for very light camping gear.