Detached eddy simulation of hydrokinetic turbine wake in shallow water depths

El Fajri, Oumnia, Bowman, Joshua, Bhushan, Shanti and O'Doherty, Tim ORCID: https://orcid.org/0000-0003-2763-7055 2024. Detached eddy simulation of hydrokinetic turbine wake in shallow water depths. Ocean Engineering 306 , 118083. 10.1016/j.oceaneng.2024.118083

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Abstract

Detached eddy simulations (DES) have been performed for flow over a solitary hydrokinetic turbine for two different tip-speed ratios λ = 3.64 and 6.15 and three different tip-clearances (δ = 0.1D, 0.2D, and 0.35D) to elucidate the effect of air-water interface on the turbine performance and wake recovery in shallow water conditions. The power predictions show good agreement with experimental data for λ = 3.64, but a large 12% error for λ = 6.15. The interface introduced unsteadiness in the power predictions, which increased with λ. The interface did not affect the mean power predictions for lower λ significantly, but reduced power for higher λ. The two-phase simulations for λ = 6.15 showed significant improvement in wake deficit and near-wake TKE prediction compared to the single-phase simulations. The improved predictions were identified because the interface causes early tip vortex entanglement and TKE burst. The DES predictions also show turbulence anisotropy maps consistent with the experimental data. Analysis reveals that turbulence is one-dimensional, dominated by streamwise fluctuations behind the blade tip region; two-dimensional, dominated by transverse and spanwise fluctuations in the TKE burst region; and approaches three-dimensional isotropy in the fully developed wake region. Detailed analysis of the vortical structures and wake characteristics reveals that the interface significantly affects the vortex advection, breakdown, and wake evolution. In particular, they enhance the wake deficit, which slows down the advection of the tip vortex filaments, causing an early vortex entanglement. The tip vortices show interaction with vortices generated underneath the interface, but these interactions seem localized. The tip vortex breakdown was identified due to instabilities generated during vortex entanglement and interaction with interface vortices for λ = 6.15 case, and because of tip and root vortex interaction for λ = 3.64. Although the two-phase simulations are encouraging compared to the single-phase case, TKE is still underpredicted in the near-wake region, possibly because of turbulence or rotating interface modeling issues. Two-phase simulations also predict significantly higher swirl, which needs further investigation.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Engineering
Additional Information:	License information from Publisher: LICENSE 1: URL: http://creativecommons.org/licenses/by-nc-nd/4.0/, Start Date: 2026-05-13 CU author has left university, AAM not able to track down. See ORCA mail message from ENGIN OA 21/05/2023. I.R.
Publisher:	Elsevier
ISSN:	0029-8018
Date of Acceptance:	1 May 2024
Last Modified:	21 May 2024 10:22
URI:	https://orca.cardiff.ac.uk/id/eprint/168965

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