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Abstract
In the design of modern wind turbines with long and slender rotor blades it becomes increasingly important to model and understand the evolving aeroelastic eects in more details. Standard stateoftheart aeroelastic simulation tools for wind turbines usually employ a blade element momentum (BEM) based aerodynamic model which is computationally cheap but includes several limitations and corrections in order to account for threedimensional and unsteady eects. The present work discusses the development of an aeroelastic simulation tool where highfidelity computational fluid dynamics (CFD) is used to model the aerodynamics of the flexible wind turbine rotor. Respective CFD computations are computationally expensive but do not show the limitations of the BEMbased models. It is one of the first times that highfidelity fluidstructure interaction (FSI) simulations are used to model the aeroelastic response of an entire wind turbine rotor.
The work employs a partitioned FSI coupling between the multibodybased structural model of the aeroelastic solver HAWC2 and the finite volume CFD solver EllipSys3D. In order to establish an FSI coupling of sufficient time accuracy and sufficient numerical stability several coupling strategies are investigated and implemented. The considered coupling strategies incorporate both loose and strong coupling schemes and employ both a conservative and a nonconservative force and deflection transfer. In a specific assessment of the implemented coupling schemes it was found that a relatively simple loosely coupled algorithm with a nonconservative force transfer is wellsuited to establish a second order time accurate and sufficiently stable FSI simulation. The use of a strong coupling scheme was found to be redundant.
Results of the partitioned FSI coupling between HAWC2 and EllipSys3D (HAWC2CFD) were then compared to the computations of the standalone solver of HAWC2 which employs traditional BEM theory to model the aerodynamics. In a first set of comparative simulations the quasisteady aeroservoelastic response of the NREL 5MW reference wind turbine was investigated for the wind speed range between 4 m/s and 24 m/s. In a second test case the same turbine was modelled during an emergency shutdown due to a loss of power in which the rotor blades are quickly pitched to feather in order to slow down the turbine. The rapid change in the aerodynamic loading and the severe structural response evoke complex flow regimes which are rather challenging to model with the traditional BEMbased models. The comparisons between the results of HAWC2CFD and HAWC2 revealed a very good agreement in the predicted aeroservoelastic response of the modelled wind turbine, although some smaller discrepancies could be found in the predicted aerodynamic forces.
Additionally, the work includes the description of a generic coupling framework which was developed in order to establish the desired partitioned coupling between HAWC2 and EllipSys3D. The developed framework was then used to also conduct FSI simulations of isolated twodimensional and threedimensional aerofoil sections by coupling a simple three degrees of freedom structural model with the respective CFD model.
The work employs a partitioned FSI coupling between the multibodybased structural model of the aeroelastic solver HAWC2 and the finite volume CFD solver EllipSys3D. In order to establish an FSI coupling of sufficient time accuracy and sufficient numerical stability several coupling strategies are investigated and implemented. The considered coupling strategies incorporate both loose and strong coupling schemes and employ both a conservative and a nonconservative force and deflection transfer. In a specific assessment of the implemented coupling schemes it was found that a relatively simple loosely coupled algorithm with a nonconservative force transfer is wellsuited to establish a second order time accurate and sufficiently stable FSI simulation. The use of a strong coupling scheme was found to be redundant.
Results of the partitioned FSI coupling between HAWC2 and EllipSys3D (HAWC2CFD) were then compared to the computations of the standalone solver of HAWC2 which employs traditional BEM theory to model the aerodynamics. In a first set of comparative simulations the quasisteady aeroservoelastic response of the NREL 5MW reference wind turbine was investigated for the wind speed range between 4 m/s and 24 m/s. In a second test case the same turbine was modelled during an emergency shutdown due to a loss of power in which the rotor blades are quickly pitched to feather in order to slow down the turbine. The rapid change in the aerodynamic loading and the severe structural response evoke complex flow regimes which are rather challenging to model with the traditional BEMbased models. The comparisons between the results of HAWC2CFD and HAWC2 revealed a very good agreement in the predicted aeroservoelastic response of the modelled wind turbine, although some smaller discrepancies could be found in the predicted aerodynamic forces.
Additionally, the work includes the description of a generic coupling framework which was developed in order to establish the desired partitioned coupling between HAWC2 and EllipSys3D. The developed framework was then used to also conduct FSI simulations of isolated twodimensional and threedimensional aerofoil sections by coupling a simple three degrees of freedom structural model with the respective CFD model.
Original language  English 

Publisher  DTU Wind Energy 

Number of pages  182 
ISBN (Print)  9788792896742 
Publication status  Published  2013 
Series  DTU Wind Energy PhD 

Number  0033(EN) 
Keywords
 DTU Wind Energy PhD0033(EN)
 DTU Wind Energy PhD0033
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Dive into the research topics of 'Partitioned FluidStructure Interaction for Full Rotor Computations Using CFD'. Together they form a unique fingerprint.Projects
 1 Finished

Coupling of a CFD Solver with a Multibody Structural Model Applied to Trailing Edge Flaps
Heinz, J. C., Sørensen, N. N., Zahle, F., Mikkelsen, R. F., Johansen, J. & Voutsinas, S.
01/10/2009 → 27/08/2013
Project: PhD