Parameterisation of intra array effects around Wind Turbine Monopiles

Abstract

Project II is a continuation of project I which studied the effects of wave incidence angle and current interaction around offshore Wind Turbine Monopiles. This report presents a brief recap of project I findings and objectives before identifying the experimental methodology used for lab testing, post processing and results analysis. Laboratory testing conducted in the Plymouth Coast basin used a 1:50 scale Monopile to replicate the prototype site and conditions of Scroby Sands Offshore Windfarm. Turbulent Kinetic Energy (TKE) and Bed Shear Stress were measured across the wake region as part of this testing, enabling a number of conclusions to be drawn. Firstly, it was noted when wave and current propagation directions were more aligned a higher level of TKE is noted at both bed and free stream level, this was seen to decay to background levels along the downstream centreline from the Monopile at around 14 diameters at free stream level. At bed level it took 8 Monopile diameters downstream to decay which was different to that predicted in Rogan’s (2015) work. Secondly, the turbulent wake region was seen to have rotated anticlockwise under wave conditions to align more with incident wave direction; this was particularly seen when wave propagation angles aligned with those of the current. Thirdly, Bed Shear Stress was observed along the downstream centreline from the Monopile. Although no clear relationships were observed, it was noted that a slightly higher level of Bed Shear Stress was seen when waves and currents were propagated at perpendicular angles. This testing also confirmed that the observed Bed Shear Stress, when scaled, matched in magnitude that of Scroby Sands prototype site. The need for research in this specific area of current and wave interaction around Monopiles is of high importance in order to bring down development costs of offshore renewables therefore a number of recommendations for further research have been made in this report.