Proposed mechanism of thrust enhancement.

Schematic of the proposed mechanistic basis of elevated circulation of vehicles with (A) flexible margins relative to those with (B) rigid margins. Kinematics of the flexible margin during bell contraction creates a large low pressure region between the bell margin and the inflexion point. This creates a suction that entrains high velocity flow in the region of the inflexion point. In contrast, higher pressure along the subumbrellar surface ejects fluid from under the bell. The difference in pressure between the two regions generates increased circulation by the extruded fluid that joins flow at the inflexion point to coalesce into a broader vortex at margins of bells with flexible flaps (A) relative to those without flexible flaps (B). (C) The pressure and (D) velocity vector fields around the bell margin of the scyphomedusa Aurelia aurita during bell contraction demonstrate the presence of a low pressure region extending from the bell margin to the inflexion point and maximum fluid velocities in the vicinity of the inflexion point, respectively.