Coherent vorticity extraction in 3D homogeneous isotropic turbulence: Influence of the Reynolds number and geometrical statistics

Abstract

The coherent vorticity extraction method (CVE) is based on the nonlinear filtering of the vorticity field projected onto an orthonormal wavelet basis made of compactly supported functions. CVE decomposes each turbulent flow realization into two orthogonal components: a coherent and an incoherent random flow. They both contribute to all scales in the inertial range, but exhibit different statistical behavior. We apply CVE to 2563 subcubes extracted from 3D homogeneous isotropic turbulent flows at different Taylor microscale Reynolds numbers (Rλ = 140,240 and 680), computed by a direct numerical simulation (DNS) at different resolutions (N = 2563,5123 and 20483), respectively. We compare the total, coherent and incoherent vorticity fields obtained by using CVE and show that few wavelets coefficients are sufficient to represent the coherent vortices of the flows. Geometrical statistics in term of helicity are also analyzed and the λ2 criterion is applied to the filtered flow fields.