Small-scale wind turbines were not considered viable in the past due to their poor
efficiencies, mainly because of their aerodynamic effects around the irfoil shape. Recently
researchers have renewed interest in enhancing the aerodynamic performances of the blades’
designs inspired by the aerodynamic pattern of biological characteristics of insects and
marine mammals such as locusts, dragonflies, damselflies, Humpback Whales etc. Bioinspired
wing designs have advantages compared to conventional smooth irfoil blades as they
can counter the bending forces that the wings experience during flapping.
Bio-inspired corrugated airfoil based on dragonfly wing geometries have been reported to
perform well compared to conventional airfoil at low Reynolds numbers. Corrugated airfoils
reduce flow separation and enhance aerodynamic performance by trapping vortices in the
corrugations thus drawing flow towards the airfoil’s surface. This results in the higher lift
whilst incurring only marginally higher drag. Such airfoils also have an advantage when it
comes to span-wise structural stiffness due to the corrugated cross-sections.
Replacing conventional turbine blades by tubercles or corrugated blades could enhance
turbine performance by reducing the pressure gradient along the leading edge; however, the
aerodynamic effects at the leading edge will depend on the variations of wavelength and
amplitude.
In this study, two types of computational studies were investigated: Optimising a corrugated
airfoil and investigating the aerodynamic effects of a sinusoidal shape at the leading edge of a
blade.
Previous studies used an idealized geometry based on the dragonfly wing cross-section
profile but did not attempt to optimize the geometry. In the present study: a two-dimensional
CFD model is constructed using ANSYS Fluent Workbench-Design Explorer to determine
the optimal corrugated blade profile for four angles of attack (AOA) from 5° to 20°
corresponding to typical AOA of small-scale wind turbine blades.
Two modified blades with variations of wavelength and amplitude at the leading edge were
studied to investigate the aerodynamic effects. Three-dimensional models were constructed
using Qblade software and 3D points were exported to AutoCAD Inventor to generate the
CAD model. The governing equations used are continuity and Navier-Stokes equations
written in a frame reference rotating with the blade. The CFD package used is ANSYS FLUENT 19.0. The simulation was run under steady-state, using SST-k omega turbulence
model.
The modifications have improved the aerodynamic performance. The optimised corrugated
blade produced a maximum increase of CL and L/D.
Both modified blades (1 and 2) had their performances measured separately and compared to
that of baseline blade SG6042 (Conventional blade). Modified blade 1 had a lower
wavelength and amplitude at the leading edge of 14.3 % and 4 % respectively of the chord. It
was noted that the aerodynamic performance decreased by 6%. Modified model 2, on the
other hand had a higher wavelength and amplitude at the leading edge. of 40.4 % and 11.9 %
respectively of the chord. It was also noted the aerodynamic performance increased by 6%.
From the empirical evidence highlighted above, it can be observed that there is a direct
correlation between wavelength, amplitude, and aerodynamic performance of the blade. / Electrical and Mining Engineering / M. Tech. (Engineering)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:unisa/oai:uir.unisa.ac.za:10500/27838 |
| Date | 31 January 2021 |
| Creators | Nemirini, Tshamano |
| Contributors | Ho, Wei Hua |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | 1 online resource (xii, 80 leaves) : Illustrations (mostly color), color photographs, application/pdf |
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