Computational Analysis of Tandem Floating Offshore Wind Turbines under Coupled Pitch-Surge Motion: A Comparative Study of the NREL 5 MW and the IEA 22 MW Turbines

Computational Analysis of Tandem Floating Offshore Wind Turbines under Coupled Pitch-Surge Motion: A Comparative Study of the NREL 5 MW and the IEA 22 MW Turbines | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Computational Analysis of Tandem Floating Offshore Wind Turbines under Coupled Pitch-Surge Motion: A Comparative Study of the NREL 5 MW and the IEA 22 MW Turbines Bin Xie, Yihan Wang, Yumeng Cai, Zi-Lu Ouyang, Chi Zhu, Guibin Tan, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6591333/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 21 Nov, 2025 Read the published version in Scientific Reports → Version 1 posted 11 You are reading this latest preprint version Abstract This study conducts a comparative CFD analysis of tandem-configured floating offshore wind turbines, in which the upstream National Renewable Energy Laboratory (NREL) 5 Megawatt (MW) and the International Energy Agency (IEA) 22 MW turbines are under coupled pitch-surge motion. Increasing pitch-surge amplitudes suppress the mean thrust of upstream turbines but enhance the thrust of stationary downstream turbines. The upstream IEA 22 MW turbine uniquely exhibits increased mean power generation with larger motion amplitudes, despite transient power losses during the downstroke phases. Compared to the upstream NREL 5 MW turbine, the upstream IEA 22 MW turbine operates at a higher angle of attack, exceeding the static stall angle, and undergoes a more severe and prolonged dynamic stall, marked by a substantially expanded flow separation zone and elevated reverse flow velocity magnitudes, particularly in the wingtip region. In contrast, downstream turbines do not show detectable dynamic stall. Although divergent wake velocity distributions are observed between the NREL 5 MW and IEA 22 MW turbines, increased pitch-surge amplitudes enhance flow velocity recovery, expanding the high-speed region and reducing the low-speed zone. Turbulent kinetic energy (TKE) levels in the wake of the IEA 22 MW turbine are decreased relative to the NREL 5 MW turbine, suggesting that dynamic blade kinematics associated with pitch-surge amplitudes improve velocity recovery through enhanced wake mixing. Furthermore, wingtip vortices coalesce into thicker three-dimensional (3-D) vortex rings as the motion amplitudes increase, with increasing downstream skewness. In the two-dimensional (2-D) planes, the vortex stripe of upstream IEA 22 MW turbine undergoes an early breakdown, interacting with the vorticity stripe of the downstream turbine to form a meandering topology. These results elucidate the physical mechanisms that govern the flow dynamics and turbine performance and provide a foundational framework for refined aerodynamic designs, the unified similarity wake model, and improved spatial configuration of wind farm arrays. Physical sciences/Engineering/Mechanical engineering Physical sciences/Energy science and technology/Renewable energy/Wind energy Floating offshore wind turbine pitch-surge motion dynamic stall vortex dynamics Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 21 Nov, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 29 Jun, 2025 Reviews received at journal 27 Jun, 2025 Reviews received at journal 18 Jun, 2025 Reviewers agreed at journal 06 Jun, 2025 Reviewers agreed at journal 03 Jun, 2025 Reviewers agreed at journal 02 Jun, 2025 Reviewers invited by journal 30 May, 2025 Editor assigned by journal 22 May, 2025 Editor invited by journal 19 May, 2025 Submission checks completed at journal 16 May, 2025 First submitted to journal 05 May, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Increasing pitch-surge amplitudes suppress the mean thrust of upstream turbines but enhance the thrust of stationary downstream turbines. The upstream IEA 22 MW turbine uniquely exhibits increased mean power generation with larger motion amplitudes, despite transient power losses during the downstroke phases. Compared to the upstream NREL 5 MW turbine, the upstream IEA 22 MW turbine operates at a higher angle of attack, exceeding the static stall angle, and undergoes a more severe and prolonged dynamic stall, marked by a substantially expanded flow separation zone and elevated reverse flow velocity magnitudes, particularly in the wingtip region. In contrast, downstream turbines do not show detectable dynamic stall. Although divergent wake velocity distributions are observed between the NREL 5 MW and IEA 22 MW turbines, increased pitch-surge amplitudes enhance flow velocity recovery, expanding the high-speed region and reducing the low-speed zone. Turbulent kinetic energy (TKE) levels in the wake of the IEA 22 MW turbine are decreased relative to the NREL 5 MW turbine, suggesting that dynamic blade kinematics associated with pitch-surge amplitudes improve velocity recovery through enhanced wake mixing. Furthermore, wingtip vortices coalesce into thicker three-dimensional (3-D) vortex rings as the motion amplitudes increase, with increasing downstream skewness. In the two-dimensional (2-D) planes, the vortex stripe of upstream IEA 22 MW turbine undergoes an early breakdown, interacting with the vorticity stripe of the downstream turbine to form a meandering topology. 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