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Nanjing Center for Ocean-Atmosphere Dynamical Studies

Multiscale interaction in geofluid flows

Fluid control

Conanical transfer have also been validated in a control experiment of the wake behind a circular cylinder. Through computing canonical transfer one can identify the intrinsic sources of perturbation of an unstable fluid flow, which are usually limited within some localized regions, and more often than not they do not correspond to the observed growth of disturbances. Shown in the following is a saturated Karman vortex street (top), with maximal rate of growth observed along the axis x=0. But the computed canonical transfer takes positive values (and maximized) only at two small side lobes near the cylinder. By experiment, inhibiting the canonical transfer in these regions suppresses most efficiently the vortex shedding in the wake, forcing the unstable flow back to the mean state. Shown below is the vorticity evolution after a control is placed at t=50 (nondimensional time units); one can see that the vortices disappear completely after t=78.