The physics of random shearing by zonal flows and the consequent reduction of scalar field transport are studied. In contrast to mean shear flows, zonal flows have a finite autocorrelation time and can exhibit complex spatial structure. A random zonal flow with a finite correlation time τ ZF decorrelates two nearby fluid elements less efficiently than a mean shear flow does. The decorrelation time is τ D=(τ η/τ ZFΩ 2 rms) 1/2 (τ n is the turbulent scattering time, and Ω rms is the rms shear), leading to larger scalar field amplitude with a slightly different scaling (∝τ D/Ω rms), as compared to the case of coherent shearing. In the strong shear limit, the flux scales as ∝Ω rms -1.
ASJC Scopus subject areas
- Condensed Matter Physics