Fluid Dynamics and Passive Scalar Transport Driven by Non-Uniform Tumbling of a Prolate Spheroid in Simple Shear Flow

TL;DR

This study uses high-fidelity simulations to analyze how non-uniform tumbling of a prolate spheroid in shear flow influences passive scalar transport, revealing effects of particle inertia, tumbling mode, and flow parameters on scalar distribution and transport rates.

Contribution

It provides new insights into scalar transport mechanisms around tumbling spheroids, highlighting the impact of particle inertia and tumbling uniformity on flow patterns and scalar transport.

Findings

Particle inertia affects tumbling and flow patterns.

Scalar lines form and merge in the wake region.

Increased particle inertia enhances scalar transport rate.

Abstract

Using high-fidelity numerical simulations based on a lattice Boltzmann framework, the advection-enhanced transport of a passive scalar from a prolate spheroid in simple shear flow has been thoroughly investigated across various parameters, including the spheroid's aspect ratio, particle-to-fluid density ratio, Reynolds number, and Schmidt number. The Reynolds number is constrained to the range from 0 to 1, where the prolate spheroid tumbles around its minor axis, aligned with the vorticity axis, in an equilibrium state. Several key findings have emerged: 1) Particle inertia significantly influences the uniformity of the spheroid's tumbling, affecting flow patterns around the spheroid and, consequently, the modes of scalar transport; 2) Both uniform and non-uniform tumbling generate a scalar line in the fluid with elevated scalar concentration, which sweeps through the wake region and merges with clusters of previously formed scalar lines; 3) Fluid passing over the spheroid carries the passive scalar downstream along these scalar lines; 4) Variations in the uniformity of spheroid tumbling result in distinct flow patterns and scalar transport modes, leading to different transport rates; 5) Within the studied parameter ranges, increased particle inertia enhances the scalar transport rate; 6) When both fluid and particle inertia are minimal, the dimensionless scalar transport rate for different aspect ratios converges to a common dependence on the Peclet number. These phenomena are analyzed in detail.