Marine Current Turbines - Siemens
Improve and de-risk the design of tidal turbine device.
Marine Current Turbines deployed their 1.2MW SeaGen turbine in Strangford Lough in 2008. It was the first renewable marine energy project to be accredited by OFGEM, and is capable of generating 6,000MWh per year. Since then, the client has built up a wealth of operational experience which they are now using to inform the design of the next-generation 2MW turbine.
The SeaGen design consists of a horizontal crossbeam supporting a rotor and generator at each end. One of the key lessons learned from the Strangford Lough turbine concerned the hydrodynamic interaction between the crossbeam and the rotor. When the tide is flowing in one direction, the rotor is upstream of the crossbeam and there is minimal interaction between the two components. However, when the tide flows in the other direction, the rotor is in the wake of the crossbeam. This imparts an impulsive load on the rotor blades which is transmitted through to the rest of the structure. This makes a contribution to the fatigue loading on the existing machine. The client asked Frazer-Nash for advice on how to minimise this loading in the 2MW design.
We built a series of models to understand the hydrodynamic interaction between the rotor blade and the crossbeam. These included:
- a high-fidelity unsteady 3D CFD model to capture the full physics of the interaction and provide accurate estimates of the resulting loading
- a simpler, more computationally-efficient model which could be used to compare the fatigue loading from different crossbeam designs and fairing designs quickly and cost-effectively
Both classes of models were validated against measured data from the 1.2MW turbine.
We analysed a wide variety of concepts, ranging from simple tapered fairings to much more novel designs and assessed the effect that each had on the fatigue loads and power performance of the turbine. This information also increased the clients' understanding of some of the key requirements on the structural design of the blade.
The results of the analysis were used to select and refine a crossbeam design concept that would minimise fatigue loads on the machine. The information also proved invaluable in informing the blade design which would reduce dynamics problems once in service. This represented a substantial de-risking of the design.