2134/11871921.v1
Chris Keylock
Chris
Keylock
Turbulence at the Lee bound: maximally non-normal vortex filaments and the decay of a local dissipation rate
Loughborough University
2020
vortex dynamics
turbulence theory
isotropic turbulence
Science & Technology
Technology
Physical Sciences
Mechanics
Physics, Fluids & Plasmas
Physics
VELOCITY-GRADIENT TENSOR
RESTRICTED EULER
EVOLUTION
IDENTIFICATION
MODEL
VORTICITY
ALIGNMENT
DYNAMICS
FLUID
TUBE
Fluids & Plasmas
Mathematical Sciences
Engineering
2020-02-20 13:16:46
Journal contribution
https://repository.lboro.ac.uk/articles/journal_contribution/Turbulence_at_the_Lee_bound_maximally_non-normal_vortex_filaments_and_the_decay_of_a_local_dissipation_rate/11871921
© 2019 Cambridge University Press. This paper uses a tight mathematical bound on the degree of the non-normality of the turbulent velocity gradient tensor to classify flow behaviour within vortical regions (where the eigenvalues of the tensor contain a conjugate pair). Structures attaining this bound are preferentially generated where enstrophy exceeds total strain and there is a positive balance between strain production and enstrophy production. Lagrangian analysis of homogeneous, isotropic turbulence shows that attainment of this bound is associated with relatively short durations and an upper limit to the spatial extent of the flow structures that is similar to the Taylor scale. An analysis of the dynamically relevant terms using a recently developed formulation (Keylock, J. Fluid Mech., vol. 848, 2018, pp. 876-904), highlights the controls on this dynamics. In particular, in high enstrophy regions it is shown that the bound is attained when normal strain decreases rather than when non-normality increases. The near absence of normal total strain results in a source of intermittency in the dynamics of dissipation that is hidden in standard analyses. It is shown that of the two terms that contribute to the non-normal production dynamics, it is the one that is typically smallest in magnitude that is of greatest importance within these filaments. The typical distance between filament centroids is just less than a Taylor scale, implying a connection to the manner in which flow topology at the Taylor scale explains dissipation at smaller scales.