Preferential orientation of tracer spheroids in evolving Taylor–Green vortex flow

Abstract

Rod- and disk-like particles preferentially align parallel and perpendicular, respectively, to the fluid vorticity, both at the early as well as later stages of the unsteady Taylor–Green vortex (TGV) flow. The early stage of the flow is laminar and comprises anisotropic large-scale Taylor–Green structures, while the later stages resemble homogeneous isotropic turbulence with Kolmogorov-type small-scale structures. The reason for the orientational behavior of inertialess spheroids in the early stage of the TGV-flow has been sought by examining the alignments of spheroidal particles, not only with vorticity but also with Lagrangian stretching and compression directions of the fluid elements in our earlier paper [Jayaram et al., “Alignment and rotation of spheroids in unsteady vortex flow,” Phys. Fluids. 33, 033310 (2021)]. This article is a sequel to the above paper in which the spheroids' alignments are studied locally, in contrast to the volume-averaged statistics studied previously, to observe the influence of the local flow field on the spheroidal alignment. It has been observed through our studies that the alignments vary periodically in space and these variations can be associated with the large-scale periodicity of the flow field originating from the initial conditions of the TGV flow. Additionally, the intense vortex stretching in the early stages of the flow evolution is seen to be largely influencing the orientation of the spheroids.