Orientation and rotation dynamics of triaxial ellipsoidal tracers in wall turbulence

Abstract

The rotational dynamics of triaxial ellipsoidal particles in turbulent channel flow have been explored. The non-inertial particles were tracked in a Lagrangian approach in an Eulerian flow field that resulted from a direct numerical simulation. Although the tracer particles translated along with the local fluid, they did not adhere to the local fluid rotation. The triaxial ellipsoids were characterized by two independent shape parameters that both were varied from 0.1 to 10. In spite of the anisotropic velocity field in the channel center, the tumbling of the particles closely resembled earlier results in homogeneous isotropic turbulence. The orientation of the particles varied substantially from the center to the near-wall region where triaxial particles tended to align their major axis in the mean flow direction and their minor axis in the wall-normal direction. These preferential alignments caused the ellipsoid to tumble as a rod about the major axis and like a disk about the minor axis. These observations show the dual nature of triaxial ellipsoids embedded in real turbulence.