Abstract:
The aim of this thesis is to study the effects of turbulent flow on a fixed pitch
tidal current turbine from the perspective of turbine design and operation. A
prototype turbine, Deltastream as it is known, is being developed by Tidal
Energy Ltd for deployment in Ramsey Sound, Wales. It is well known that
turbulence plays an important role in the fatigue life of marine turbines. Field
measurements of tidal flow at the turbine site were analysed to establish the
velocity spectra and turbulence intensity. This revealed a wide range of
anisotropic turbulence which is dependent upon the tidal direction with
intensities ranging from 5-20%.
A numerical turbine model based on momentum theory was constructed in a
time marching formulation that accounts for the effects of dynamic inflow and
rotationally augmented airfoil stall delay properties. The turbine rotor design
allows for load alleviation by regulation of the turbine tip speed ratio. At flow
velocities above the rated velocity the tip speed ratio can be increased to
reduce turbine loads. The model has been combined with a novel rotor speed
control algorithm that estimates unsteady turbine inflow velocity from turbine
loading without the requirement for external sensing of flow speed. When the
turbine is subjected to three dimensional turbulent inflow the rotor speed
controller has been shown to significantly reduce the fatigue effect of unsteady,
turbulent flow. The turbine blade design has been developed using the model
established. Experimental validation studies were carried out at 1/16th scale in
turbulent conditions.
Studies using the model have; identified the relationship between turbulence
intensity and turbine fatigue load, established a controller schedule to
significantly reduce fatigue loading and determined the blading fatigue life in
realistic turbulent flows.
