Have any experiments been performed on how to maximize atmospheric drag on a surface? While looking for any research on maximizing drag, all of my searches produce studies on how to minimize drag. Is anyone aware of experiments performed to maximize drag on a surface? Is it even possible to increase drag above that supplied by a rough surface?
 A: Imagine a sphere moving through air. You can increase its drag by increasing the "apparent" diameter of the sphere by populating its surface with bumps or projections with sharp edges on them that stick out into the free stream air flow.
Note also that as the air flows around the sphere, it has a difficult time following the curve on the backside of the sphere at higher speeds- and beyond a certain point, the flow separates from the backside of the sphere and a zone of low pressure forms in the ball's wake. The larger the separation area, the more drag force will be applied to the sphere by the lowered pressure inside the separation zone.
Interestingly, flow separation can be delayed by stirring up or energizing the boundary layer surrounding the skin of the sphere. One way to do this is to populate the skin of the sphere with small concave divots or dimples. The amount of separated flow on the backside of the sphere will be less than in the case of a perfectly smooth sphere, which is the reason that golf balls are dimpled: the dimpled ball flies farther than the smooth one.
Finally, if you make the front surface of the object flat instead of smoothly curved, you can trigger flow separation right at the sharp edge of the flat and create a wake which is significantly wider than the object itself, where the wake zone is full of low pressure air which then acts on the backside of the object to slow it down.
A: I can't give you any proven answer. In my imagination, I see lots of stiff hairs or spikes extending from the surface. They would be spaced far enough apart that significant moving air would travel among them, rather than have a boundary layer that most of the air flowed around.
And after seeing @Niels Nielsen's answer, it might be good to put little balls on the ends of some of those spikes.
And in my imagination, it might be possible to have some small vortex ring generators on the surface. The ones I've seen all depended on single shocks to generate single vortex rings, but possibly you could have something that oscillated in a wind to produce long series of them. perhaps at angles. The closer you get to two vortex rings traveling in opposite directions, the more that their energy is just a drain. And they might help disrupt other airflows to increase drag. That's a series of assumptions, and any or all of them could be wrong, but it's what my imagination gave me.
A: Off the top of my head:

*

*parachute;

*aerodynamic brake and spoiler;

*thrust reverser;

*the lower surface of the space shuttle during reentry phase.

