| dc.description.abstract | A bluff body, i.e. an object with blunt rather than streamlined shape, exposed to
external flow gives rise to a multitude of flow patterns depending on the timeand
length-scales, the free-stream velocity, and the viscosity of the fluid. In this
work, three-dimensional numerical solutions of the Navier–Stokes equations are
used to study the physics of two interesting cases of flow past bluff bodies. The
first is the turbulent wake behind a curved circular cylinder. This is an important
flow configuration for the offshore industry because it represents a model to study
the flow past catenary risers and curved pipelines. Carefully validated direct numerical
simulations are the basis for the identification of upper and lower wake
regions with distinctly different flow dynamics. Results concerning turbulence in
the wake, vortex dynamics, secondary flows, and instabilities in the shear layers,
are presented and discussed. The second problem addressed is that of oscillatory
flow around cylinders, with focus on the primary vortical instability for circular
and elliptic cross-sections. New findings for both cylindrical configurations are
reported in the light of vortical structures and time-series analysis of velocity and
vorticity samples. Furthermore, predictions from a previous stability theory for
elliptic cylinders are confirmed for the first time. | nb_NO |
