Preprints
https://doi.org/10.5194/wes-2023-88
https://doi.org/10.5194/wes-2023-88
18 Aug 2023
 | 18 Aug 2023
Status: a revised version of this preprint was accepted for the journal WES and is expected to appear here in due course.

An insight into the capability of the Actuator Line Method to resolve tip vortices

Pier Francesco Melani, Omar Sherif Mohamed, Stefano Cioni, Francesco Balduzzi, and Alessandro Bianchini

Abstract. The Actuator Line Method (ALM) is being increasingly preferred to the ubiquitous Blade Element Momentum (BEM) approach in several applications related to wind turbine simulation, thanks to the higher level of fidelity required by the design and analysis of modern machines. This approach, however, still falls behind other medium-fidelity methodologies such as the Lifting Line Theory (LLT) when it comes to resolving the vortex-like structures shed at the blade tip (i.e., tip vortices) and their effect on the load profile along the blade. Despite the numerical strategies proposed so far to overcome this limitation, the reason for such behaviour is still unclear. Moving from this background, in this study the ALM’s capability to simulate tip effects is investigated. To this end, the ALM tool developed by the authors in the ANSYS® FLUENT® environment (v. 20.2) was employed for the simulation of a NACA0018 finite wing, for different pitch angles. Three different test cases were considered: high-fidelity blade-resolved CFD simulations, to be used as a benchmark, standard ALM, and ALM with the spanwise force distribution coming from blade-resolved data (frozen ALM). The last option was included to isolate the effect of force projection, using three different smearing functions. For the post-processing of the results, two different techniques were applied: the LineAverage sampling of the local angle of attack along the blade and state-of-the-art Vortex Identification Methods (VIM) to outline the blade vortex system. The analysis showed that the ALM can account for tip effects without the need of additional corrections, provided that the correct angle of attack sampling and force projection strategies are adopted.

Pier Francesco Melani, Omar Sherif Mohamed, Stefano Cioni, Francesco Balduzzi, and Alessandro Bianchini

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wes-2023-88', Luca Greco, 27 Sep 2023
    • AC1: 'Reply on RC1', Alessandro Bianchini, 22 Dec 2023
  • RC2: 'Comment on wes-2023-88', Thomas Potentier, 22 Nov 2023
    • AC2: 'Reply on RC2', Alessandro Bianchini, 22 Dec 2023

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wes-2023-88', Luca Greco, 27 Sep 2023
    • AC1: 'Reply on RC1', Alessandro Bianchini, 22 Dec 2023
  • RC2: 'Comment on wes-2023-88', Thomas Potentier, 22 Nov 2023
    • AC2: 'Reply on RC2', Alessandro Bianchini, 22 Dec 2023
Pier Francesco Melani, Omar Sherif Mohamed, Stefano Cioni, Francesco Balduzzi, and Alessandro Bianchini
Pier Francesco Melani, Omar Sherif Mohamed, Stefano Cioni, Francesco Balduzzi, and Alessandro Bianchini

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Short summary
The paper makes use of a multi-fidelity approach, also including blade-resolved CFD, to assess to what extent the Actuator Line Method is able to properly resolve the flow phenomena in finite blade (tip effects). It proved that alternative kernel shapes are not influential on accuracy, while demonstrates that the ALM can provide better results if the characteristic length of both force smearing and angle of attack sampling from the flow field decrease approaching the blade extremity.
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