Tidal turbine blade load experiments for oscillatory motion

This paper presents blade root bending moment
measurements of a horizontal-axis tidal turbine for planar
oscillatory motion, conducted in a stationary water towing tank.
By comparing the measurements with quasi-steady reconstructions
for both single and multiple frequency oscillatory
motion, the bending moment was shown to be sensitive to both
frequency and amplitude, as well as to the mean tip-speed ratio.
The unsteady loads associated with the separation of the flow
and dynamic stall are shown to be of considerably greater
importance than those which are already present for attached
flow, such as added mass and dynamic inflow. A linear model fit
to the unsteady bending moment also indicates that the inertia
contribution is relatively small.

For cases where attached flow exists over the majority of the
load cycle, these reconstruction methods are likely to be sufficient
to obtain a reasonable prediction of the root out-of-plane bending
moment. However, turbines whose blades are likely to operate
near stall are likely to require more complex models for accurate
load predictions to mitigate the risk of fatigue failure