Licentiate seminar: Linus Sundberg

Fluid, particles, and their ineractions

Abstract

Particles suspended in a fluid form an interacting system, where the fluid exerts hydrodynamic forces and torques on the particles, and the particles generate disturbances in the fluid flow. For large particles, there are two types of inertia involved in the dynamics of the particle suspension: (i) particle inertia and (ii) fluid inertia.

Particle inertia, measured by the dimensionless Stokes number, allows particles to detach from the flow. This implies that nearby particles can have very large velocity differences. The underlying multivalued particle-velocity field is formed when the phase-space manifold folds over (caustic). Here, we investigate how the tails of the fluid-velocity gradient distribution affect caustic formation.

Fluid inertia, measured by the non-dimensional particle Reynolds number, affects the hydrodynamic forces and torques on the suspended particles. The fluid inertia corrections to the hydrodynamic force and torque are given as polynomials in the relative velocity and angular velocity of particle and fluid. In this thesis, we derive constraints upon the coefficients of the polynomials based on particle-shape symmetries. These constraints are used to predict the fluid-inertial correction to the torque on a curved fibre settling in a quiescent fluid and determine the orientation of which the wire settles. The predicted tilt angle is found to be in qualitative agreement with experimental measurements on settling fibres in quiescent air.

Opponent: Srdjan Sasic

Supervisor: Bernhard Mehlig

Extra supervisor: Kristian Gustavsson

Examiner: Mattias Marklund