Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Comparison of Different Wind Turbine Modeling Strategies in CFD Simulations
Maokun Ye

Department of Ocean Engineering, Texas A&M University
College Station, Texas, USA

Hamn-Ching Chen

Zachry Department of Civil Engineering and Department of Ocean Engineering, Texas A&M University
College Station, Texas, USA

Arjen Koop

MARIN – Maritime Research Institute Netherlands
Wageningen, The Netherlands

ABSTRACTINTRODUCTION

Computational Fluid Dynamics (CFD) tools are now widely used in the
aerodynamic analysis of wind turbines. To simulate the turbine different
modelling techniques are available with different levels of complexity
and accuracy. In CFD simulations with fully resolved rotor geometries,
one common approach is to resolve the blades and hub only whileneglecting the supporting tower. The main advantage of this approach isthat it circumvents the need to model the relative motion between
rotating blades and the stationary tower. As a result, steady-state CFD
simulations can be performed, and the computational resources aresignificantly reduced. On the other hand, however, the unsteady natureof the turbulent flow generated by the turbine blades is not properly
captured, and the effects of the tower on both the near and far wakes are
entirely ignored.

To be a major clean energy source that supplies one-third of the total
electricity demand by 2050, more wind farms need to be deployedworldwide, and more efficient wind turbines and wind farms need to be
designed (Veers et al., 2019). Different modelling techniques withdifferent levels of complexity and accuracy have been widely adopted inwind turbine CFD simulations. One commonly used approach tocalculating the flow around and behind a wind turbine is to couple theRANS or LES solvers with Blade element method (BEM) based methods.
In these calculations, the influences of wind turbines are modeled asforces in the fluid field, thus the need of resolving the geometry of theblades and the fluid boundary layers is omitted (Troldborg, 2009). Thisapproach is in particular popular in the wind turbine wake simulations,examples can be found in Troldborg (2009), Wu and Porté-Agel (2015),and Xie and Archer (2017). The adoption of these approaches is often
inevitable when it comes to calculations of wind turbine wakes because
it is extremely resource-demanding to resolve both the turbine boundary
layers and the wake regions at the same time. However, those methods
may be questioned as they usually assume that the flow on the surface ofthe blades is 2 dimensional and this may not be physically correct in thereal world (Duque, 1999).

In the present study, the NTNU Blind Test 1 wind turbine is calculated
in CFD simulations by three different approaches: 1) steady-state
simulations by Absolute Formulation Method (AFM) for the rotor – onlygeometry; 2) unsteady simulations by Moving-Grid Formulation Method(MVG) for the rotor – only geometry; 3) unsteady simulations by MVG
for the complete rotor, nacelle, and tower geometry. For all simulations,
Reynolds Averaged Navier-Stokes (RANS) simulations with the 𝑘𝑘 − 𝜔𝜔
SST turbulence model are performed. First, the numerical uncertainties
are quantified to ensure the validity of the results. Then, for each of theconfigurations, the thrust coefficients (𝐶𝐶𝑇𝑇 ) and power coefficients (𝐶𝐶𝑃𝑃 )are calculated under the inlet velocity of 10 m/s and the tip speed ratio(TSR) of 6. The wake velocity profiles are obtained, and the vorticalstructures from the rotor are visualized. Finally, the CFD results arecompared among each other and against the measured data to provide
insights into the effects of the different modeling approaches in windturbine CFD simulations.

In recent years, thanks to the continual decrease of computational cost,
CFD simulations with fully resolved rotor geometries are becoming
increasingly popular in wind turbine simulations. In those calculations
which resolve the geometry of the turbine blades and the corresponding
boundary layers, two different approaches of handling the turbine
rotation exist.
The first approach is to resolve the rotor only while ignoring thesupporting structure. By doing this, steady-state simulations can be
performed because the relative motion between the rotor and thesupporting tower is absent. As a result, the computational resource is

KEY WORDS: CFD; Wind Turbine; Wake Effects; Numerical
Uncertainties; Verification.

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