2022/09/06 by Aluie, Hussein, Rai, Shikhar, Yin, Hao +5
#FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn)
paper · doi:10.48550/arxiv.2209.02819
We highlight the differing roles of vorticity and strain in the transport of coarse-grained scalars at length-scales larger than ℓ by smaller scale (subscale) turbulence. %subscale flux/stress which appear in the evolution of coarse-grained (resolved) scalars/momentum account for the effect of (subgrid) scales smaller than the coarse-graining length ℓ. We use the first term in a multiscale gradient expansion due to Eyink \citeEyink06a, which exhibits excellent correlation with the exact subscale physics when the partitioning length ℓ is any scale smaller than that of the spectral peak. We show that unlike subscale strain, which acts as an anisotropic diffusion/anti-diffusion tensor, subscale vorticity's contribution is solely a conservative advection of coarse-grained quantities by an eddy-induced non-divergent velocity, \bv_*, that is proportional to the curl of vorticity. Therefore, material (Lagrangian) advection of coarse-grained quantities is accomplished not by the coarse-grained flow velocity, \OL\bu_ℓ, but by the effective velocity, \OL\bu_ℓ+\bv_*, the physics of which may improve commonly used LES models.