kth.sePublications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Non-iterative smearing correction for the actuator line method
KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.ORCID iD: 0000-0001-9360-7300
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.ORCID iD: 0000-0002-5913-5431
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.ORCID iD: 0000-0001-7864-3071
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The actuator line method (ALM) is extensively used in wind turbine and rotor simulations. However, its original uncorrected formulation overestimates the forces near the tip of the blades and does not reproduce well forces on translating wings. The recently proposed smearing correction for the ALM is a correction based on physical and mathematical properties of the simulation that allows for a more accurate and general ALM. So far, to correct the forces on the blades, the smearing correction depended on an iterative process at every time step, which is usually slower, less stable and less deterministic than direct methods. In this work, a non-iterative process is proposed and validated. First, we propose a formulation of the non-linear lifting line that is equivalent to the ALM with smearing correction, showing that their results are practically identical for a translating wing. Then, by linearizing the lifting line method, the iterative process of the correction is substituted by the direct solution of a small linear system. No significant difference is observed in the results of the iterative and non-iterative corrections, both in wing and rotor simulations. Additional contributions of the present work include the use of a more accurate approximation for the velocity induced by a smeared vortex segment and the implementation of a free-vortex wake model to define the vortex sheet, that contribute to the accuracy and generality of the method. The results present here may motivate the adoption of the ALM by other communities, for example, in fixed-wing applications.

National Category
Fluid Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-318305OAI: oai:DiVA.org:kth-318305DiVA, id: diva2:1696976
Note

QC 20221003

Available from: 2022-09-19 Created: 2022-09-19 Last updated: 2025-02-09Bibliographically approved
In thesis
1. On stability of vortices and vorticity generated by actuator lines
Open this publication in new window or tab >>On stability of vortices and vorticity generated by actuator lines
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Vortices are present in nature and in many flows of industrial importance. The stability of configurations of vortices can have real-world consequences, because vortices play a crucial role in accelerated mixing. In particular, vortices are present in the wake of wind turbines and other rotors. Their blades create a system of multiple helical tip and hub vortices in the wake. The stability of the tip vortices greatly influences the wake recovery behind a turbine and, consequently, can affect the power production and fatigue of a downstream wind turbine in clustered wind farms. Also, concentrated vortices can cause vortex-structure interaction which increases vibration and noise. In this work, the stability of vortices is studied by analytical models and Navier-Stokes simulations. The vorticity generated in these simulations was studied in order to develop improvements to the numerical methods used to simulate blades and wings.

Numerical simulations of a moving rotor, representing a floating offshore wind turbine, showed that the wake is dominated by the stability modes predicted by the linear stability theory. Also, the observation that the stability of helical vortices has properties that can be related to the stability of a two-dimensional row of vortices, also noted previously in other works, motivated the development of a new formulation to study the stability of two-dimensional potential flows, based on the bicomplex algebra. Models based on vortex filaments and the Biot-Savart law were developed to study the stability of the system of multiple helical vortices created by turbine blades. The results indicate that the linear stability of the tip vortices is independent of the linear stability of the hub vortices (and vice-versa). For more complex configurations, such as two in-line turbines or blades that create multiple vortices near the tip, the numerical simulations and analytical studies indicate a more complex scenario, with multiple vortices interacting.

The Navier-Stokes simulations employ the actuator line method (ALM), which is a method used to model blades that allows coarser grids, reducing computational costs. In this method, the blades are represented by body forces that are calculated from the local flow velocity and airfoil data. However, until recently, the actuator line method misrepresented the forces near the tip of the blades. The recently developed vortex-based smearing correction resolved some of these limitations. In this work, the understanding of the vorticity generated by actuator lines is used to develop more accurate corrections for the velocity induced by a smeared vortex segment and for the magnitude of the vorticity generated in the simulations. Also, a non-iterative procedure for the smearing correction is proposed based on the lifting line method. These modifications improve the agreement of the ALM with a non-linear lifting line method. For the first time, configurations typical of airplane aerodynamics are simulated with the ALM, such as a wing with winglets and a combination of horizontal and vertical tails. The accuracy of these results may motivate other communities to adopt the ALM for a diverse set of applications, beyond rotor aerodynamics.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2022
Series
TRITA-SCI-FOU ; 2022:46
National Category
Fluid Mechanics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-318631 (URN)978-91-8040-348-1 (ISBN)
Public defence
2022-10-13, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
KTH Royal Institute of Technology
Note

QC 220922

Available from: 2022-09-22 Created: 2022-09-22 Last updated: 2025-02-09Bibliographically approved

Open Access in DiVA

No full text in DiVA

Other links

https://arxiv.org/abs/2206.05448v1

Authority records

Kleine, Vitor G.Hanifi, ArdeshirHenningson, Dan S.

Search in DiVA

By author/editor
Kleine, Vitor G.Hanifi, ArdeshirHenningson, Dan S.
By organisation
Fluid Mechanics and Engineering AcousticsLinné Flow Center, FLOWSeRC - Swedish e-Science Research Centre
Fluid Mechanics

Search outside of DiVA

GoogleGoogle Scholar

urn-nbn

Altmetric score

urn-nbn
Total: 82 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf