Most shapes aren’t streamlined for fluid flow. We call these bulky, often boxy shapes, bluff bodies. Above, we see two examples of a bluff body, a flat plate, in a soap film. On the left, the plate sits perpendicular to the soap film’s top-to-bottom flow. Two large, counter-rotating vortices form behind the plate and a wide wake stretches behind it.
On the right, we see the same flat plate but now a long, flexible filament is attached to either end. As the flow moves past, it deforms the filament, creating a rounded shape. Researchers found that, under the right conditions, this flexible afterbody could reduce drag on the object by up to 10%. (Image and research credit: S. Gao et al.)