scholarly journals Development of a Simulation Tool Coupling Hydrodynamics and Unsteady Aerodynamics to Study Floating Wind Turbines

2017 ◽  
Author(s):  
Vincent Leroy ◽  
Jean-Christophe Gilloteaux ◽  
Maxime Philippe ◽  
Aurélien Babarit ◽  
Pierre Ferrant
Keyword(s):  
Wind Turbines ◽  
Unsteady Aerodynamics ◽  
Offshore Wind ◽  
Computational Time ◽  
Vortex Wake ◽  
Rotor Wake ◽  
Free Vortex ◽  
Code Validation ◽  
Floating Offshore Wind Turbines ◽  
Wake Interactions

Depending on the environmental conditions, floating Horizontal Axis Wind Turbines (FHAWTs) may have a very unsteady behaviour. The wind inflow is unsteady and fluctuating in space and time. The floating platform has six Degrees of Freedom (DoFs) of movement. The aerodynamics of the rotor is subjected to many unsteady phenomena: dynamic inflow, stall, tower shadow and rotor/wake interactions. State-of-the-art aerodynamic models used for the design of wind turbines may not be accurate enough to model such systems at sea. For HAWTs, methods such as Blade Element Momentum (BEM) [1] have been widely used and validated for bottom fixed turbines. However, the motions of a floating system induce unsteady phenomena and interactions with its wake that are not accounted for in BEM codes [2]. Several research projects such as the OC3 [3], OC4 [4] and OC5 [5] projects focus on the simulation of FHAWTs. To study the seakeeping of Floating Offshore Wind Turbines (FOWTs), it has been chosen to couple an unsteady free vortex wake aerodynamic solver (CACTUS) to a seakeeping code (InWave [6]). The free vortex wake theory assumes a potential flow but inherently models rotor/wake interactions and skewed rotor configurations. It shows a good compromise between accuracy and computational time. A first code-to-code validation has been done with results from FAST [7]on the FHAWT OC3 test case [3] considering the NREL 5MW wind turbine on the OC3Hywind SPAR platform. The code-to-code validation includes hydrodynamics, moorings and control (in torque and blade pitch). It shows good agreement between the two codes for small amplitude motions, discrepancies arise for rougher sea conditions due to differences in the used aerodynamic models.

scholarly journals Comparison of Free Vortex Wake and BEM Structural Results Against Large Eddy Simulations Results for Highly Flexible Turbines Under Challenging Inflow Conditions

2022 ◽  
Author(s):  
Kelsey Shaler ◽  
Benjamin Anderson ◽  
Luis A. Martinez-Tossas ◽  
Emmanuel Branlard ◽  
Nick Johnson
Keyword(s):  
Wind Turbines ◽  
Economic Benefits ◽  
Offshore Wind ◽  
Elastic Response ◽  
Vortex Wake ◽  
Free Vortex ◽  
Floating Offshore Wind Turbines ◽  
Wind Energy Development ◽  
The Many ◽  
Inflow Conditions

Abstract. Throughout wind energy development, there has been a push to increase wind turbine size due to the substantial economic benefits. However, increasing turbine size presents several challenges, both physically and computationally. Modeling large, highly flexible wind turbines requires highly accurate models to capture the complicated aerodynamic response due to large deflections and nonstraight blade geometries. Additionally, development of floating offshore wind turbines requires modeling techniques that can predict large rotor and tower motion. Free vortex wake (FVW) methods model such complex physics while remaining computationally tractable to perform the many simulations necessary for the turbine design process. Recently, a FVW model—cOnvecting LAgrangian Filaments (OLAF)—was added to the National Renewable Energy Laboratory engineering tool OpenFAST to allow for the aerodynamic modeling of highly flexible turbines along with the aerohydro- servo-elastic response capabilities of OpenFAST. In this work, FVW and low-fidelity blade-element momentum (BEM) structural results are compared to high-fidelity simulation results for a highly-flexibly downwind turbine for varying TI, shear exponent, and yaw misalignment conditions. Through these comparisons, it was found that for all considered quantities of interest, SOWFA, OLAF, and BEM results compare well for steady inflow conditions with no yaw misalignment. For OLAF results, this strong agreement was consistent for all yaw misalignment values. The BEM results, however, deviated significantly more from SOWFA results with increasing absolute yaw misalignment. Differences between OLAF and BEM results were dominated by yaw misalignment angle, with varying shear exponent and TI leading to more subtle differences. Overall, OLAF results were more consistent than BEM results when compared to SOWFA results under challenging inflow conditions.

An Unsteady Aerodynamics Model for Lifting Line Free Vortex Wake Simulations of HAWT and VAWT in QBlade

2016 ◽  
Author(s):  
Juliane Wendler ◽  
David Marten ◽  
George Pechlivanoglou ◽  
Christian Navid Nayeri ◽  
Christian Oliver Paschereit
Keyword(s):  
Wind Turbines ◽  
Turbine Blades ◽  
Unsteady Aerodynamics ◽  
Vortex Method ◽  
Vertical Axis ◽  
Empirical Method ◽  
Vortex Wake ◽  
Simulation Code ◽  
Free Vortex ◽  
Lifting Line

This paper describes the introduction of an unsteady aerodynamics model applicable for horizontal and vertical axis wind turbines (HAWT/VAWT) into the advanced blade design and simulation code QBlade, developed at the HFI of the TU Berlin. The software contains a module based on lifting line theory including a free vortex wake algorithm (LLFVW) which has recently been coupled to the structural solver of FAST to allow for time-resolved aeroelastic simulations of large, flexible wind turbine blades. The aerodynamic model yields an accuracy improvement with respect to Blade Element Momentum (BEM) theory and a more practical approach compared to higher fidelity methods such as Computational Fluid Dynamics (CFD) which are too computationally demanding for load case calculations. To capture the dynamics of flow separation, a semi-empirical method based on the Beddoes-Leishman model now extends the simple table lookups of static polar data by predicting the unsteady lift and drag coefficients from steady data and the current state of motion. The model modifications for wind turbines and the coupling to QBlade’s vortex method are described. A 2D validation of the implementation is presented in this paper to demonstrate the capability and reliability of the resulting simulation scheme. The applicability of the model is shown for exemplary HAWT and VAWT test cases. The modelling of the dynamic stall vortex, the empiric model constants as well as the influence of the dynamic coefficients on performance predictions are investigated.

A Formulation for the Unsteady Aerodynamics of Floating Wind Turbines, With Focus on the Global System Dynamics

2017 ◽  
Author(s):  
Ilmas Bayati ◽  
Marco Belloli ◽  
Luca Bernini ◽  
Alberto Zasso
Keyword(s):  
System Dynamics ◽  
Wind Turbines ◽  
Unsteady Aerodynamics ◽  
Offshore Wind ◽  
Scale Model ◽  
Wind Tunnel Experiments ◽  
Global System ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Thrust And Torque

This paper proposes a formulation for the assessment of the unsteady aerodynamics of floating offshore wind turbines, based on wind tunnel experiments through surge and pitch imposed motions on the 1/75 DTU 10 MW scale model. Rotor thrust and torque were analysed out of a set of different combinations of amplitudes and frequencies of the imposed mono-harmonic motion, following the idea of splitting these forces into steady and unsteady contributions, respectively through steady and unsteady aerodynamic coefficients. The latter were analysed, for different tip-speed ratios, both experimentally and numerically, with respect to a newly introduced parameter, the “wake reduced velocity”, which turned out to be effective in the description of the unsteady regime. Experimental results have shown good consistency of the formulation and put the basis for further studies on this topic, for the comprehension of this phenomenon and for the development of reduced-order models for control purposes, with the focus of the global system dynamics.

scholarly journals UNAFLOW: a holistic wind tunnel experiment about the aerodynamic response of floating wind turbines under imposed surge motion

2021 ◽  
Vol 6 (5) ◽  
pp. 1169-1190
Author(s):  
Alessandro Fontanella ◽  
Ilmas Bayati ◽  
Robert Mikkelsen ◽  
Marco Belloli ◽  
Alberto Zasso
Keyword(s):  
Wind Tunnel ◽  
Wind Turbines ◽  
Lift Coefficient ◽  
Unsteady Aerodynamics ◽  
Wind Tunnel Experiment ◽  
Tip Vortex ◽  
Offshore Wind ◽  
Hysteresis Cycle ◽  
Floating Offshore Wind Turbines ◽  
Blade Tip

Abstract. Floating offshore wind turbines are subjected to large motions due to the additional degrees of freedom of the floating foundation. The turbine rotor often operates in highly dynamic inflow conditions, and this has a significant effect on the overall aerodynamic response and turbine wake. Experiments are needed to get a deeper understanding of unsteady aerodynamics and hence leverage this knowledge to develop better models and to produce data for the validation and calibration of existing numerical tools. In this context, this paper presents a wind tunnel experiment about the unsteady aerodynamics of a floating turbine subjected to surge motion. The experiment results cover blade forces, rotor-integral forces, and wake. The 2D sectional model tests were carried out to characterize the aerodynamic coefficients of a low-Reynolds-number airfoil with harmonic variation in the angle of attack. The lift coefficient shows a hysteresis cycle close to stall, which grows in strength and extends in the linear region for motion frequencies higher than those typical of surge motion. Knowledge about the airfoil aerodynamic response was utilized to define the wind and surge motion conditions of the full-turbine experiment. The global aerodynamic turbine response is evaluated from rotor-thrust force measurements, because thrust influences the along-wind response of the floating turbine. It is found that experimental data follow predictions of quasi-steady theory for reduced frequency up to 0.5 reasonably well. For higher surge motion frequencies, unsteady effects may be present. The turbine near wake was investigated by means of hot-wire measurements. The wake energy is increased at the surge frequency, and the increment is proportional to the maximum surge velocity. A spatial analysis shows the wake energy increment corresponds with the blade tip. Particle image velocimetry (PIV) was utilized to visualize the blade-tip vortex, and it is observed that the vortex travel speed is modified in the presence of surge motion.

Pitch Angle Control of Floating Offshore Wind Turbines by H∞ Control

2014 ◽  
Vol 134 (8) ◽  
pp. 1096-1103 ◽  
Author(s):  
Sho Tsujimoto ◽  
Ségolène Dessort ◽  
Naoyuki Hara ◽  
Keiji Konishi
Keyword(s):  
Wind Turbines ◽  
Pitch Angle ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines
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