Non-local amplification of intense vorticity in turbulent flows

Abstract

The nonlinear and nonlocal coupling of vorticity and strain-rate constitutes a major hindrance in understanding the self-amplification of velocity gradients in turbulent fluid flows. Utilizing highly-resolved direct numerical simulations of isotropic turbulence in periodic domains of up to $12288^3$ grid points, and Taylor-scale Reynolds number $R_{\lambda }$ in the range $140-1300$, we investigate this non-locality by decomposing the strain-rate tensor into local and non-local contributions obtained through Biot-Savart integration of vorticity in a sphere of radius $R$. We find that vorticity is predominantly amplified by the non-local strain coming beyond a characteristic scale size, which varies as a simple power-law of vorticity magnitude. The underlying dynamics preferentially align vorticity with the most extensive eigenvector of non-local strain. The remaining local strain aligns vorticity with the intermediate eigenvector and does not contribute significantly to amplification; instead it surprisingly attenuates intense vorticity, leading to breakdown of the observed power-law and ultimately also the scale-invariance of vorticity amplification, with important implications for prevailing intermittency theories.

6 pages, 6 figures

References in corpus (4)

• Local and Nonlocal Strain Rate Fields and Vorticity Alignment in Turbulent Flows
• Direct Assessment of Vorticity Alignment with Local and Nonlocal Strain Rates in Turbulent Flows
• Extreme dissipation and intermittency in turbulence at very high Reynolds numbers
• Generation of intense dissipation in high Reynolds number turbulence

Cited by in corpus (4)

• Generation of intense dissipation in high Reynolds number turbulence
• Intermittency of turbulent velocity and scalar fields using 3D local averaging
• Scaling of acceleration statistics in high Reynolds number turbulence
• Lagrangian acceleration in fully developed turbulence and its Eulerian decompositions