Drag reduction and wake mitigation in wind turbines using riblet microstructures

McEvoy, Daniel J. (2020) Drag reduction and wake mitigation in wind turbines using riblet microstructures. [USQ Project]

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Wind turbines suffer many inefficiencies under immensely dynamic conditions. Turbulence, whether systemic or deliberately induced, generates far wake fields that deplete kinetic energy for downstream installations. This study will examine the use of a geometrical feature known as ‘riblets’, applied to the surface of turbine blades to reduce drag and mitigate wake effects.

Riblets were inspired by dermal denticles in shark skin, capable of reducing shear forces in the boundary layer. Previous studies into the use of man-made riblets focused on uniform designs across the aerofoil without giving consideration to bespoke designs that would address the complex varying shear forces and turbulent kinetic energy regions of the boundary layer. Computational fluid dynamic software was used to validate a known NACA 0012 aerofoil against experimental and simulated values from the National Aeronautics and Space Administration (NASA). Variations were then made to both uniform and non-uniform riblet configurations ranging in size from 50 to 125 micrometers along the chord length of an NACA 0012 standard symmetrical aerofoil. These included uniform and non-uniform riblet designs from fore to aft chordwise.

3D simulations were be completed using SOLIDWORKS Flow Simulation to measure free stream velocity and static/dynamic pressures across eight (8) aerofoils at wind speeds ranging from 5-90 m/s. A further four (4) S-802 wind turbine blade aerofoils were modelled and the methodology repeated. Comparing drag coefficients resulted in an overall decrease in performance of the riblet aerofoils, contrary to previous experimental studies. Drag was greater by up to 20% at lower velocities with the detriment decreasing as wind velocity increased.

It is likely that computational fluid dynamic software is unable to account for the complex nature of vortex control in the boundary layer. Whilst it may be able to resolve the generation and estimate the effects, when considering that the underlying mechanism for raising, pinning and separating vortices is not completely understood in experimentation, it would follow that software packages are yet to incorporate what is still a somewhat unknown phenomenon and it is likely cost prohibitive to develop.

This document describes the development of the project from original idea initiation to a fully scoped research project and resultant findings. This proposal includes a comprehensive literature review, proposed methodology of research, project scheduling, costs, risk assessment, risk mitigation and quality control planning. This research reaffirms the lack of precise understanding as to exactly why experimental riblet designs are able to yield drag reductions. Despite there being very reasonable assumptions it is likely still beyond even very complex CFD software algorithms. The research therefore indicates that in order to apply knowledge to wind turbine blade design, experimental data is not expected to corroborate simulations and practical application for research should be the starting point for drag reduction and the control of turbulent vortex generation in the field of fluid mechanics until greater practical understanding is achieved.

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Item Type: USQ Project
Item Status: Live Archive
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Mechanical and Electrical Engineering (1 Jul 2013 - 31 Dec 2021)
Supervisors: Saleh, Khalid
Qualification: Bachelor of Engineering (Honours) (Mechanical)
Date Deposited: 16 Aug 2021 05:40
Last Modified: 26 Jun 2023 04:16
URI: https://sear.unisq.edu.au/id/eprint/43047

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