Stirring Faces
These dramatic curlicues were generated by a computer simulation of the motion of a small body — in this case a flat, rigid plate — through an incompressible fluid, such as water or, in some conditions, air. Each of the four images depicts the same phenomenon, but at a different point in time. The "eyes" of the facelike pictures correspond to vortices of turbulence caused by the motion of the plate through the fluid. "Two direct goals of the research are to better understand how birds and insects fly, and to develop unsteady aerodynamic models for advanced micro-aerial vehicles," says Steve Brunton, a graduate student in Princeton's department of mechanical and aerospace engineering.

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