Understanding
of hydrodynamics involved in the flow around tidal turbines is
essential to enhance their performance and resilience, as they are
designed to operate in harsh marine environments. During their
lifespan, they are subjected to high velocities with large levels of
turbulence that demand their design to be greatly
optimised. Experimental tests have provided valuable information
about the performance of tidal stream devices but these are often
conducted in
constricted flumes featuring turbulent flow conditions different
to those found at deployment sites. Additionally, measuring
velocities at prospective sites is costly and often dificult. Numerical
methods arise as a tool to be used complementary to the experiments
in investigations of tidal stream turbines. In this thesis, a high-fi
delity large-eddy simulation computational approach is adopted and
includes the immersed boundary method for body representation, due to
its ability to deal with complex moving geometries. The
combination of these numerical methods offers a great balance between
computational resources and accuracy. The approach is applied and
validated with simulations of vertical and horizontal axis tidal
turbines, among other challenging cases such as a pitching
airfoil. An extensive validation of predicted hydrodynamics, wake
developed downstream of the devices or structural loadings, outlines the
accuracy of the proposed computational approach. In the simulations of
vertical axis tidal turbines, the blade-vortex
interaction is highlighted as the main phenomenon dominating the physics
of these devices. The horizontal axis tidal turbine is simulated under
different flow and turbulence intensity conditions, in both at and
irregular channel bathymetries. This thesis seeks
to assess and enhance the performance, resilience and survivability of
marine hydrokinetic devices in their future deployment at sea.