by Tom&Shelly » Fri Apr 15, 2022 10:30 am
In my career, I worked on a few aerodynamic studies, and suffice it to say, it's a very difficult problem to analyze in detail and make predictions about. That said, the general idea is that creating turbulent air is bad. It takes energy to make turbulence, which of course comes, ultimately, from your fuel. The square back on that trailer is particularly bad in that regard since the air tries to move into the (relative) vacuum created behind the trailer as it moves down the road. As the air moves in, it creates turbulence. The intent of the baffles is to help smooth the airflow in the back and reduce the volume of vacuum that the air tries to move into. But we all already know all of that.
There are three ways to study the problem, only one of which seems to be practical for us. The first would be to use a super computer* to try and figure out the best length, and angles for the baffles, and the second would be to build accurate scale models and test in a wind tunnel. The practical method is to make some reasonable looking baffles and experiment on the road. My guess is that your first attempt will produce the biggest improvement, and any tweeks thereafter will be minor, but I might be wrong about that.
Tom
* Be wary of web sites that claim to allow computer analysis and read the fine print. Turns out they implement the equations using 2 dimensions, which is fine for students studying the phenomena of turbulence, but the results will be entirely incorrect in the details, including our situation, which is fundamentally based on a 3D world!