Brief on Status Report 2012

The Beta version of the “Offwind code” has been developed and now the evaluation process has been started. The purpose is to learn how well the program succeeded in achieving its ultimate goal and thereafter, the code will be further developed in the next two years (2013-14).

The code has been developed to be an “Open source” and mainly for industrial purposes (engineers and not necessarily researcher). Looking to this, we have put lots of time and effort to develop a very user friendly interface and in two different levels:

  • Engineering Level (based on empirical equations): While engineers can easily get the results in accurate level and very fast (minutes). This will be mainly Web based design. The Engineering level will include: Meso Wind, Wake Simulation and Wind wave Power calculation)
  • Advanced Level (CFD): Using Google Earth, wind data and based on our CFD solver (Offwind solver- based on OpenFoam). This part will be a combination of web- Cloud- based and local installation. This will include: Pre-Processing. Solver and Post Processing

Further description

The project aims to develop a prediction tool for Prediction tools for offshore wind energy generation. The tool will be employed for advanced operation assessment and forecasting for offshore wind farms. This will lead to optimal localization of a wind farm and how to allocate future farms with respect to each other within the same wind energy cluster. The predicting the interaction between wind farms and turbines becomes important for optimized wind energy production or large installations offshore, considering the fact that the flow of wind between windmills is influenced by other windmills – both on a small and large scale wind farm.

This objective was tackled in two distinct approaches: a) an engineering strategy, by which the regional climatology is characterised by long-term wind data series obtained from publicly available databases; b) an advanced strategy, where the local mesoscale winds are modelled using a mesoscale meteorological model, namely the Weather Research and Forecast (WRF) model, from which boundary conditions are subsequently extracted to drive the microscale CFD simulations. Two approaches are implemented to allow the inclusion of the regional climatology within computational fluid dynamic (CFD) of wind flow over offshore wind farms.

In present work package a turbine wake interaction model is developed. Two methods for accounting the wake from the wind turbines are discussed: engineering method based on the Jenson approach and CFD based on implicit modelling of the wind turbines. The engineering tool is based on velocity deficit approach and it is named as OffWindEng. In CFD approach the turbines are modelled as a momentum sink in 3D Navier Stokes (NS) equation. The momentum sink is based on Actuator Line (AL) approach, which is developed from the SOWFA code and implemented in PisoFoam solver within OpenFoam architecture. The extended code is named as an OffWindSolver. The results from OffWindEng and OffWindSolver are compared with a real windfarm located at Lillgrund, Sweden/Denmark.

Because of the scale of a computation, we only examine the effect of wind from one direction at one speed. In absence of real time depending atmospheric boundary profile, a log wind velocity profile with surface roughness of 0.04. The simulated power production of the turbines in the wind turbine farm is compared to the field data and large-eddy simulation (LES). The overall plant power is well predicted with OffWindSolver but large discrepancy with OffWindEng is observed. The simulation shows the significant decreases of the power for some of the turbines those were in wake.

On the wind-wave interaction side, A CFD solver has been developed and validated to compare the ABL over a flat wall with offshore ABL over ideal 2D waves moving with and against the wind direction. Large Eddy Simulation (LES) approach to model turbulence which has the ability to provide detailed descriptions of turbulent flow at large Reynolds number with reasonably computational cost is used to investigate the effect of moving wavy wall on the velocity profile and flow structures.

An engineering tool has also developed to show the scatter in predicted velocity and turbine power output values by using different wave parameterization models. The primary results of the test cases show the ability of the developed code to solve the offshore ABL. Waves show a tendency to alter the velocity and turbulent fields in offshore ABL and these effects extend to cover the depth of ABL where wind turbines are usually placed. More detailed and accurate LES simulations are needed to quantify the surface wave effects on offshore ABL.

Our main goal as a part of Offwind project is to deal with managing and implementing the software development process. Offwind team consists of a strong part of research persons and to deliver their results (models, solver codes, databases etc.) to end users we did a full analysis of the situation and proposed ways of how this can be presented.

Conclusion

Open source code is available at GitHub: https://github.com/OffWind

Offwind tools application is here, on this web-site. Tools become available after registration.

For now (end of 2012) the following aspects have been covered:

  • Web-site creation
  • Engineering Tools (web-application)
  • Advanced Tools / CFD (web-application coupled with back-end server)
  • Advanced Tools / CFD (desktop-application for Windows platforms, experimental for users who don't have access to web)