In this paper, we analyze the three-dimensional (3D) instabilities observed in two flows, both of which comprise dominant coherent vortices that are deformed elliptically by strain rate effects. These flows are the counter-rotating vortex pair and the circular cylinder wake in the transition regime. In the case of the vortex pair, we compare the experimental instability growth rate, spatial structure of the internally deforming vortices, and wavelengths of instability, with predictions from the theory of elliptic 3D instability, all of which have good agreement. In the case of the transition in the cylinder wake, we provide evidence that the origin of the "mode A" 3D instability is also an elliptic instability of the highly-strained primary wake vortices. These results provide the first clear evidence of elliptic 3D instability in open flows comprising finite vortices.
展开▼
