Session: 01-06-01 CFD Modeling and Offshore Applications

Submission Number: 175826

Exploratory Energy-Budget Analysis of a Floating Wind Turbine Wake Under Pitch and Roll Motions 

Introduction:

Floating offshore wind turbines (FOWTs) are increasingly critical for unlocking wind energy potential in deep-water sites where fixed-bottom foundations are infeasible. Unlike fixed turbines, FOWTs undergo significant platform motions such as pitch, roll, surge, and heave, induced by wave and wind loading. These motions affect blade aerodynamics, wake structures, and ultimately, energy capture and farm-level performance. Existing research has characterized how pitch and roll affect wake velocity deficits, turbulence intensity, and coherent structure formation. However, these studies focus primarily on qualitative wake dynamics and performance metrics and stop short of quantitatively describing how energy is transported, diffused, and dissipated in the wake under motion conditions.

This study provides an exploratory step toward quantifying wake energy transport in floating wind turbine wakes by applying a slice-based pseudo energy budget analysis.

o      Using high-fidelity URANS with the Reynolds Stress Model, we extract velocity fields from cross-plane snapshots of a model FOWT wake and compute two-dimensional approximations of key energy transport contributions (mean/TKE advection, production, turbulent transport, diffusion, and a surrogate dissipation term).

o       We compare pitch and roll-induced wakes at representative Strouhal numbers and amplitudes, highlighting qualitative differences in how platform dynamics redistribute kinetic energy in shear layers and wake cores.

o       By integrating budget terms over coherent wake regions (defined either via vorticity thresholds or fixed windows), we obtain interpretable, order-of-magnitude indicators of energy redistribution that can inform reduced-order wake models.

While this approach does not yet provide a complete three-dimensional energy budget, it demonstrates how CFD data can be leveraged to explore how floating-platform dynamics affect energy transport pathways. The method and preliminary findings represent a first step toward bridging detailed turbulence diagnostics with reduced-order wake modeling frameworks for offshore wind applications.

CFD data and validation:

This work builds upon previous CFD studies of a model floating wind turbine subjected to harmonic pitch and roll motions. Simulations were carried out in OpenFOAM v2212 using a blade-resolved URANS framework with the Reynolds Stress Model (RSM) to capture anisotropic turbulence and coherent structures. Arbitrary Mesh Interfaces (AMI) were employed for dynamic mesh handling, enabling simultaneous resolution of rotor rotation and platform oscillations.

The turbine considered is the MoWiTO 0.6, a model-scale rotor with a diameter of 0.58 m, designed to reproduce the aerodynamic characteristics of the NREL 5 MW reference turbine. The computational mesh contained about 18 million cells, with refinement zones extending 17 rotor diameters downstream. Near-wall resolution achieved y+ values between 15 and 40, consistent with wall-function requirements. Grid and timestep independence studies confirmed robustness, with a Grid Convergence Index below 5%.

Validation against wind tunnel experiments demonstrated good agreement in power and thrust coefficients, as well as wake velocity deficit and turbulence intensity profiles, confirming the model’s accuracy under both fixed and oscillatory conditions.

Energy budgeting framework:

The balance of kinetic energy, turbulence production, and dissipation fundamentally governs the wake of a wind turbine. In this study, an instantaneous energy-budgeting framework is employed to quantify the mechanisms of energy transport and recovery in the wake of a model floating wind turbine subjected to pitch and roll motions. The method enables a term-by-term decomposition of the energy equation, highlighting how platform dynamics redistribute energy within the flow.

A surrogate two-dimensional definition of kinetic energy density is used, derived from in-plane velocity components in CFD snapshots. This simplification neglects streamwise contributions but allows consistent slice-based comparisons between pitch and roll cases. Budget terms for advection, diffusion, and dissipation are then extracted from re-gridded CFD fields obtained from blade-resolved URANS simulations. URANS with the Reynolds Stress Model was selected as a practical compromise, providing anisotropic turbulence representation at lower cost than LES or DNS.

Presenting Author: Muhammad Salman Siddiqui Norwegian univerisity of Life Sciences

Presenting Author Biography: Muhammad Salman Siddiqui is a Professor of Mechanical Engineering at the Faculty of Science and Technology, Norwegian University of Life Sciences (NMBU). Previously, he was a postdoctoral fellow and researcher at the Norwegian University of Science and Technology (NTNU), where he also earned his PhD in Applied Mathematics. He is currently the leader of the Computational Science and Engineering Research Group within his department.

His primary research focuses on numerical and computational fluid dynamics applied to engineering systems. His work includes designing and developing software for aerodynamic assessments of offshore wind turbines, modeling and simulation of renewable energy resource harvesting, evaluating heating and cooling technologies for energy-efficient buildings, and creating reduced-order, multi-scale, and physics-based models.

He has co-authored numerous scientific publications in internationally recognized peer-reviewed journals and conference proceedings. As an active member of professional organizations such as Elsevier, Scopus, the American Society of Mechanical Engineers (ASME), and the American Institute of Aeronautics and Astronautics (AIAA), He regularly reviews scientific articles, book chapters, and project proposals in fields including wind energy, computational mechanics, computational fluid dynamics, energy systems, and environmental studies. He also serves as a topic editor for leading journals, including Energies, Applied System Innovation, and Sustainability.

Authors:

Haris Hameed Mian Norwegian University of Life Sciences
Fadi Al Machot Norwegian University of Life Sciences
Arvind Keprate Oslo Metropolitan University (OsloMet)
Habib Ullah Norwegian University of Life Sciences
Muhammad Salman Siddiqui Norwegian univerisity of Life Sciences