EU-NORSEWInD - Investigation of Flow Distoration Effects on Offshore Instrumentation

Data is a key component for all offshore wind projects. As the deadline for 2020 fast approaches, offshore wind is the key area of expansion for the wind industry and EU member states in order to meet their renewable energy obligations. However there remains significant challenges ahead, not least of which is the availability of good quality data to facilitate better project planning, accurate yield prediction, and a fundamentally better understanding of the working environment and local climatology. To address this issue the common convention is to mount instrumentation in offshore locations to assess the local wind conditions. Part of the overall NORSEWInD project is the use of LiDAR remote sensing (RS) systems mounted on offshore platforms to measure wind velocity profiles at a number of locations offshore. The data acquired from the offshore RS measurements will be fed into a large and novel wind speed dataset suitable for use by the wind industry. The data will also feed into key areas such as forecasting and MESOSCALE modelling improvements. One significant problem identified early on at the NORSEWInD project planning stage was the problem of platform interference effects on the RS data. It was obvious that the airflow data measured above the mounting platforms would be distorted by the presence of the platform. However; the extent to which the flow field above the various mounting platforms would be distorted was unknown. Therefore, part of the fundamental research incorporated into the NORSEWInD project was an investigation into the possible scale and extent of the interference on the measured data of the various mounting platforms and an assessment of the possibility of correcting the recorded data for the interference effects. This paper reports on the Computational Fluid Dynamics (CFD) modelling of the wind flows over the platforms and the verification of the CFD models by the use of sub scale wind tunnel models employing three dimensional Constant Temperature Anemometers (CTAs) to measure local velocity vector data. The report also discusses how the measured RS data may be corrected for interference effects.