Analysis of turbulent bending moments in tidal current boundary layers

As ocean current turbines move from the design stage into production and installation, a better understanding of localized loading is required in order to more accurately predict turbine performance and durability. In this study, large eddy simulations (LES) of tidal boundary layers without turbines are used to measure the turbulent bending moments that would be experienced by an ocean current turbine placed in a tidal channel. The LES model captures turbulence due to winds, waves, thermal convection, and tides, thereby providing a high degree of physical realism, and bending moments are calculated for an idealized infinitely thin circular rotor disc. Probability density functions of bending moments are calculated and detailed statistical measures of the turbulent environment are also examined, including vertical profiles of Reynolds stresses, two-point velocity correlations, and velocity structure functions. The simulations show that waves and tidal velocity have the largest impacts on the strength of bending moments, while boundary layer stability and wind speeds have only minimal impacts. It is shown that either transverse velocity structure functions or two-point transverse velocity spatial correlations can be used to predict and understand turbulent bending moments in tidal channels. (C) 2015 AIP Publishing LLC.