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

Verification Study for CFD Simulations of NTNU Blind Test 1 Wind Turbine
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

several folds. To meet this requirement, more wind farms need to be
deployed worldwide, and more efficient wind turbines and wind farms
need to be designed. Computational Fluid Dynamics (CFD) methods
have become a very powerful tool in the predictions of wind turbine
performance with the continually decreasing computational cost andhave been widely used in the wind engineering industry with different
levels of fidelity. Blade element method (BEM) based approaches
coupled with RANS or LES equations have been predominant in thewind turbine simulations, examples can be found in Troldborg (2009),
Wu and Porté-Agel (2015), and Xie and Archer (2017). CFD simulations
with fully resolved rotor geometries are also becoming increasingly
popular in the predictions of wind turbine performance. Li et al. (2012)
performed CFD simulations for the NREL phase VI wind turbine byleveraging the dynamic overset technique. In the study, the geometriesof the turbine including the tower are resolved. Both the RANS and thedetached eddy simulation (DES) approaches were used in thesimulations. Lynch and Smith (2013) also investigated the NREL phaseVI turbine by using the CFD code FUN3D with unstructured oversetgrids. Tran and Kim (2016) studied the performance of the NREL 5 MWturbine under prescribed platform motions by using Star-CCM+. In thestudy, RANS equations with the 𝑘𝑘 − 𝜔𝜔 SST turbulence model are solved,
and the overset grid technique is adopted. Ye et al. (2021) performed
CFD simulations with fully resolved rotor geometry for two tandemly
arrayed wind turbines, in which steady-state RANS simulations werecarried out by using the absolute formulation method (AFM).

ABSTRACT
Computational Fluid Dynamics (CFD) simulations with fully resolved
turbine geometries are increasingly popular for wind turbine
aerodynamic analysis. However, the results obtained from the CFD
simulations are sensitive to many numerical settings, such as grid
spacing, time increment, turbulence models, etc., and thus rigorous
quantification of the numerical uncertainties is necessary to be able tohave confidence in the results.
In the present study, a modern verification procedure is adopted to assess
the numerical uncertainties in the CFD simulations. The NTNU Blind
Test 1 turbine is analyzed in the CFD simulations by using ReFRESCO.
To quantify the spatial and temporal discretization uncertainties, asimulation matrix consisting of four computational grids with different
level of resolutions combined with three different time increments isestablished. In all the computational grids, the turbine geometry is fully
resolved including the blades, hub, nacelle, and tower. Moreover, thecomputational domain for CFD simulations is constructed such that itexactly matches the wind tunnel in the NTNU Blind Test 1 experiment.
Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations withthe k-ω SST turbulence model are performed. The Moving-GridFormulation (MVG) approach with the sliding interface technique isleveraged to handle the rotating wind turbine and stationary tower andnacelle. By using a modern verification procedure, the numericaluncertainties on the thrust coefficient (𝐶𝐶𝑇𝑇 ) and power coefficient (𝐶𝐶𝑃𝑃 ) aredetermined for an inlet velocity of 10 m/s at a tip speed ratio (TSR) of 6.

However, confidence in the CFD predictions needs to be established ina proper manner when applying the CFD methods to complex flows.
Most of the aforementioned studies only compared the CFD predictions
against the experimental data, while detailed assessments of thenumerical uncertainties and experimental uncertainties were notprovided. In particular, for floating offshore wind turbines (FOWT), theaerodynamics and hydrodynamics of the wind turbines are of equal
importance, thus for each of those numerical uncertainties has to be
determined to provide confidence on the overall uncertainty from CFD

KEY WORDS: CFD; Wind Turbine; Numerical Uncertainties;

Verification.

INTRODUCTION
In order to achieve carbon neutrality in the coming decades, electricity
generation from renewable sources, including wind, will have to increase275