Large eddy simulation of tidal turbines

Understanding of hydrodynamics involved in the ow 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 umes featuring turbulent ow conditions dierent to
those found at deployment sites. Additionally, measuring velocities
at prospective sites is costly and often dicult.
Numerical methods arise as a tool to be used complementary to the
experiments in investigations of tidal stream turbines. In this thesis,
a high-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 oers 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 dierent
ow 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.