Energy and Environment

Deep sea offshore wind turbine technology

The exploitation of open sea (deep-water) wind energy resources can give access to a large number of sites with good wind conditions and less restrictions (noise, visual acceptance) than on-shore. Wind turbines used here may differ from conventional designs due to different operational conditions and absence of some restrictions.
Contact

Stenbro, Roy

Specialist Group Manager - Wind Energy

 

The KMB-project ‘Deep sea offshore wind turbine technology’ will combine wind technology know-how with offshore and energy industry experience to enhance development of deep-sea offshore wind farms. The overall objective is to advance Norwegian development within this field and to focus on technical solutions that ensure cost-efficiency of deep-sea offshore wind energy technology.

The project comprises interdisciplinary tasks that are required for the successful development of Norwegian deep-sea offshore wind technology.

The main goals and activities are:

Task 1: Development of design tools for offshore wind energy concepts

To give design activities a sound foundation, a variety of models have to be developed and tested. Offshore experience, extensive experimental investigations and the coupling of existing numerical methods from the different fields will create the necessary tools. Main goal of this task is to develop a tool-box (analytics, numerical methods and experiments) for the design of offshore wind energy concepts. Sub-goal is the design and the verification of concepts itself. The task includes institute research headed by Marintek. One Phd-study is planned on “concurrent engineering aspects for reducing loads on support structure” with Prof Geir Moe (NTNU) and Dr Kjetil Uhlen (SINTEF Energy Research) as supervisors.

Task 2: Development of large offshore rotorblades

Research activities will focus on the design of rotor blades adapted to offshore conditions. Investigation issues will be blade flexibility and operation at high tip-speed ratios. Aerodynamic devices such as winglets, vortex generators or adaptive ‘add-ons’ to increase performance of the blade will be evaluated. The estimation of the potential for adaptive technology with focus on boundary-layer manipulation to optimise aerodynamics and decrease loads will be assessed. The aerodynamic design process will be carried out with various numerical tools. Design and parameter studies, see Figure 1 will be conducted using Euler/Boundary layer solvers like XFOIL and state-of-the-art Navier-Stokes models. Aero–elastic simulations, for typical results see Figure 2 will be carried out with proven tools based on the Blade-Element-Momentum theory and new developed coupled solvers. The numerical results will be verified in wind tunnel tests at NTNU and field tests at the Norwegian test station for wind energy at Valsneset. A PhD-student will work on ‘Rotorblade tip design’ with Prof. Per Åge Krogstad and Dr. Andreas Knauer (IFE) as supervisors. The work will comprise numerical parameter studies with focus on aerodynamic performance and verification of results in wind tunnel tests at NTNU.

 

offshorefig1

Figure 1: Aerodynamic behaviour of the rotorblade profile IFE M06 compared to NACA 63415 profile

 

 

offshorefig2

Figure 2: Torque generation of a 1.5 MW rotor in the whole operational area from aero-elastic simulations with Flex5

Task 3: Connection of big offshore wind farms

The development of very large offshore wind farms in blocks of +1000 MW represent new challenges compared to land based developments. The wind may be more stable offshore, but there will be less geographical smoothing effect, so wind intermittence will still be a key issue. Power transmission and grid connection represent other main challenges for realisation of deep sea offshore wind farms. The following activities are planned for this sub-task:

- Development of systems for connection of very big offshore wind farms (bulk transmission)
- Assessment of offshore wind power intermittency and variations depending on time-scale and geographical distribution, but also possibilities to forecast production
- Case study considering offshore wind farms and electrification of oil-rigs

One PhD study is planned on this task to be supervised by Prof Tore Undeland (NTNU) and Dr Kjetil Uhlen (SINTEF Energy Research).

Actual work

IFEs project activities are today focused on advanced aerodynamic and aero-elastic simulations with state-of –the-art numerical tools. IFE’s new Linux cluster ‘Polaris’, established by ENSYS/IT/ADMIN in late 2006 is the cornerstone for such advanced simulations.

The RANS-solver TAU from DLR Göttingen will be used on the cluster for the assessment of complex rotor blade flows and design of large wind turbine rotor blades. The dynamic behaviour of complete Offshore wind turbine concepts will be analysed with the aero-elastic code FLEX 5. This will support the design of new concepts for the deep-water offshore environment. Aero-elastic models will further be coupled with models for marine hydrodynamics for simulation of the complex, multi-physical behaviour of the deepwater concepts.

Norsk Hydro ASA and UMOE RYVING AS are cooperating industry partners for IFE in this project.