Nonspherical particle suspensions in wall turbulence

Abstract

In the present PhD thesis, we investigate the dynamics of small non-spherical particles suspended in a fully developed turbulent channel flow. Non-spherical particles are approximated as axisymmetric spheroidal and triaxial ellipsoidal particles, which are characterized by their inertia and shape. As a starting point, the rotational dynamics of an inertial oblate spheroidal particle suspended in a creeping linear shear flow is investigated, which is later used in interpreting the results obtained in complex turbulent flows. The three-dimensional turbulent flow field is obtained from the Navier-Stokes equations by means of direct numerical simulation in an Eulerian reference frame. The particles are tracked using Lagrangian point particle approach. Existing methodology to simulate the prolate spheroidal particles in wall-bounded turbulent channel flow is extended to investigate the dynamics of oblate spheroidal particles and triaxial ellipsoidal particles. The effects of particle inertia, particle shape, and fluid shear on particle rotation and orientation are reported with respect to both fluid and particle reference frame. Particles at the channel center and near the wall show different rotation patterns and surprisingly different effects of particle inertia. Finally, we report the systematic investigation of the gravity force effects on the dynamics of prolate spheroidal particles.