Aerodynamic Response of a Two-Dimensional Cambered Wing at Low Reynolds Numbers in Steady-State Onset Turbulence

Small fixed-wing Unmanned Aerial Vehicles (UAVs) are valuable tools for military and civil applications. However, their utility is hampered by a lack of knowledge regarding their performance in adverse weather, notably turbulence, as seen in urban or mountainous environments. This is combined with the effects of low Reynolds numbers and consequent laminar separation. In order to improve the design of UAVs for their operating conditions, it is important to understand how a low Reynolds number aerofoil responds to turbulent flows. Furthermore, it is unclear whether camber alters this response. This research examines how a thick aerofoil responds to onset turbulence at low Reynolds numbers and whether camber influences this. A cambered and an otherwise identical symmetrical aerofoil were tested in wind tunnel conditions relevant to UAV flight, with Reynolds numbers from 50,000 to 200,000 and turbulence intensities from 1.3% to 15%. Changes in the surface pressures and loads were assessed. To evaluate the potential for predicting these effects, the aerofoils were tested under equivalent sinusoidal-pitching conditions. It was determined that turbulence has a significant effect on the performance of low Reynolds number aerofoils, and this response is also influenced by camber. The cambered aerofoil sees a significant degradation in performance as the turbulence intensity is increased, which is not observed on the corresponding symmetrical aerofoil. However, it maintains a higher lift generation capability than the symmetrical form for any given flow condition. A similar behaviour was observed when the aerofoils were pitched sinusoidally, the cambered form less readily forming leading edge vortices than its symmetrical counterpart. Both aerofoils in turbulent flow were seen to experience a form of irregular dynamic stall. While sinusoidal-pitching did produce a similar effect on the time-averaged lift coefficient to onset turbulence, the transient behaviour was strongly reflective of the unsteady motion causing it. Furthermore, low-cost dynamic stall models did not prove to be readily adapted for onset turbulent flows. However, an approximate load estimate may be possible to aid UAV design. Furthermore, the reluctance of cambered aerofoils to form vortex events may make them more suitable for smooth UAV flight through turbulence.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2020

Author dc:creator

• Kay, Nicholas John

Advisors dc:contributor.advisor

• Sharma, Rajnish N
• Richards, Peter J

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/53391

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/53391