Fluid Structure Interaction of Wind Turbines in Atmospheric Flow

The overall aim of this project, is to develop tools that can perform high fidelity simulations of the interaction between atmospheric wind and the wind turbine response. This will mean that more physically realistic simulations can be conducted, clarifying, for instance, the influence of turbulent inflow on the structural response of the turbines. 

Background

When designing wind turbines, currently industry relies on Blade Element Momentum (BEM) solvers, which are efficient, as good results are found with low computational cost. However, BEM is not suitable for all kinds of load cases, e.g. stand still operation and rotor-tower interaction, as vortices are not considered. For this reason Computational Fluid Dynamics (CFD) is gaining relevance as computational resources increase, enabling high fidelity wind flow modelling around the turbines.

As turbines increase in size and become more flexible, the need to include the structural response in the simulations becomes important. This is due to an increased risk of vortex induced vibrations and flutter instabilities. This is known as Fluid Structure Interaction (FSI), where the coupled effects of wind and structure response are studied.

In the present project, the aim is to develop further on the DTU CFD solver Ellipsys3D, which is coupled to the aero-elasticity code HAWC2 for FSI simulations. The CFD solver needs further development on overset grid features and modelling of atmospheric boundary layer flow, in order to efficiently conduct fully resolved simulations of wind turbines in atmospheric flow.

Project Objectives

The objectives of the PhD project are to:

  • Develop on the existing overset grid capabilities of Ellipsys3D
    - Motion transferring from HAWC2 to the moving subdomains needs to be established
    - Pressure coupling between subdomains is to be developed
  • Implement a hybrid turbulence model in Ellipsys3D combining Large Eddy Simulations (LES) of the atmospheric boundary layer, with a k-ω SST turbulence model close to the turbine.
  • Conduct fully resolved FSI on wind turbines in realistic simulated atmospheric flow.

Perspective

The expected outcomes of the PhD project are developments that allow us to conduct FSI simulations with fully resolved wind turbines in atmospheric flow. This will become possible as the overset grid feature enables relative motion between rotor, tower and ground. The motion will be defined through the communication with HAWC2, which calculates the structural response to the loads from CFD in a coupled manner.

The new turbulence model will make sure that realistic atmospheric inflow is modelled, while remaining computationally efficient.

Using these new features, load cases like stand still operation and tower-rotor interaction can be studied at high fidelity in realistic flow. This can help clarifying where BEM is sufficient and where it is not. Additionally high fidelity simulations can be used to make simple models of phenomena, which can be included in future BEM codes.

Contact

Christian Grinderslev
PhD student
DTU Wind Energy
+4526 35 38 09