Abstract
As wind turbine technology proceeds towards the development of more advanced and complex machines, modelling tools with fidelity higher than the ubiquitous Blade Element Momentum (BEM) method are needed. Among them, the Actuator Line Method (ALM) stands out in terms of accuracy and computational cost. Moving from this background, an advanced ALM method has been developed within the commercial solver CONVERGE®. As elements of novelty, this tool features a Lagrangian method for sampling the local inflow velocity and a piece-wise smearing function for the force projection process. Various sub-models for both Horizontal Axis Wind Turbines (HAWTs) (e.g. the Shen tip loss correction) and Vertical Axis Wind Turbines (VAWTs) (e.g. the MIT dynamic stall model) has also been included. Aim of the research is to address the new challenges posed by modern machines. HAWTs are in fact getting larger and larger, shifting the research focus on the interaction of increasingly deformable blades with the atmosphere at the micro- and mesoscale level. VAWTs on the other hand, whose popularity has arisen in the last years, thanks to their advantages in non-conventional applications, e.g. floating offshore installations, are extremely complex machines to study, due to their inherently unsteady aerodynamics. The approach has been validated on selected test cases, i.e. the DTU 10MW turbine and a real 2-blade H-rotor, for which both high-fidelity CFD and experimental data are available.
Highlights
As wind turbine technology proceeds towards the development of more advanced and complex machines, modelling tools with fidelity higher than the ubiquitous Blade Element Momentum (BEM) method are needed in an increasing number of applications
For each timestep: (a) the Aerodynamic Center (AC) of each blade element, i.e. the corresponding airfoil quarter-chord point, is located on the grid based on the turbine characteristics and operating condition; (b) the local undisturbed velocity V is extracted from the resolved Computational Fluid Dynamics (CFD) flow field and is used to evaluate the blade angle of attack α and chord-based Reynolds number Re; (c) the airfoil lift (CL) and drag (CD) coefficients are obtained via linear interpolation of the available tabulated aerodynamic data; (d) the blade element forces are inserted into the computational domain as volume momentum sources; (e) the modified unsteady Navier-Stokes set of equations is solved
For Horizontal Axis Wind Turbines (HAWTs), the present study focused on the ubiquitous DTU 10 MW RWT, originally designed by Bak et al [13] at Denmark Technical University (DTU) with the aim of creating a benchmark configuration for the generation of large scale off-shore machines
Summary
As wind turbine technology proceeds towards the development of more advanced and complex machines, modelling tools with fidelity higher than the ubiquitous Blade Element Momentum (BEM) method are needed in an increasing number of applications. Each blade is replaced by a dynamically equivalent actuator line, introducing aerodynamic forces into the computational grid based on its current position and local flow conditions. Thanks to this strategy, this method does not require the resolution of the boundary layer encompassing the blade surfaces, with a corresponding strong decrease in the required computational cost. A method of interpolating lift and drag coefficients based on the blade airfoils relative thickness has proven to be effective in reproducing blade forces calculated by a full blade-resolved CFD simulation Based on these characteristics, the developed software is supposed to be able to address the numerous challenges that arise when simulating the latest generation of wind turbines. Upon comparison of the ALM data with the benchmark ones, the developed model has proven to be a robust and reliable tool in terms of both performance and flow field description
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