Abstract
In typical industrial practice based on IEC standards, wind turbine simulations are computed in the time domain for each mean wind speed bin using a few number of unsteady wind seeds. Software such as FAST, BLADED or HAWC2 can be used to capture the unsteadiness and uncertainties of the wind in the simulations. The statistics of these aeroelastic simulations output are extracted and used to calculate fatigue and extreme loads on the wind turbine components. The minimum requirement of having six seeds does not guarantee an accurate estimation of the overall statistics. One solution might be running more seeds; however, this will increase the computation cost. Moreover, to move beyond Blade Element Momentum (BEM) based tools toward vortex/potential flow formulations, a reduction in the computational cost associated with the unsteady flow and uncertainty handling is required. This study illustrates the unsteady wind aerodynamic statistics' stationary character based on the standard turbulence models. This character is shown based on the output of NREL 5MW simulations. Afterwards, we propose a non-intrusive Polynomial Chaos Expansion approach to build a surrogate model of the loads' statistics, NREL 5MW rotor thrust and torque, at each time step, to estimate the extreme statistics more accurately and efficiently.
Highlights
The process of calculating loads on wind turbine components is one of the core parts of wind turbine aerodynamic and structural 15 design and optimization
Afterwards, based on that conclusion, we built a limited number of surrogate models for polynomial orders of 2 to 5 and show the statistics match the reference case
We can conclude that building a surrogate model on a limited number of time steps, or even one time step, is enough, and it is not necessary to create a surrogate model on every time step as predicted by the aerodynamic model form
Summary
The process of calculating loads on wind turbine components is one of the core parts of wind turbine aerodynamic and structural 15 design and optimization. In the last few decades, international organizations have developed different aeroelastic codes such as Fatigue, Aerodynamics, Structures, and Turbulence (FAST) (Jonkman et al, 2005), BLADED (Bossanyi, 2003) and HAWC2 (Larsen and Hansen, 2007) to accurately calculate load time series based on the standardized or site-specific environmental conditions. Engineers and researchers use wind turbine aeroelastic simulation output statistics to calculate extreme and fatigue loads on wind turbine structure and estimate the unsteady power. For each mean wind speed, at least six different seeded unsteady wind time series are required as the minimum to take into account the uncertainties. This limited number of unsteady simulations does not yield an entirely accurate estimation of the statistics.
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