An experimental investigation into the effects of atmospheric turbulence on the aerodynamics of micro air vehicle wings

Loxton, B 2011, An experimental investigation into the effects of atmospheric turbulence on the aerodynamics of micro air vehicle wings, Doctor of Philosophy (PhD), Aerospace, Mechanical and Manufacturing Engineering, RMIT University.


Document type: Thesis
Collection: Theses

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Title An experimental investigation into the effects of atmospheric turbulence on the aerodynamics of micro air vehicle wings
Author(s) Loxton, B
Year 2011
Abstract The aim of this research is to focus on the performance of micro air vehicles under replicated turbulent conditions such that exist on windy days, focusing on the unsteady aerodynamics and resultant transient response. It was hypothesised that the transient behaviour of the separation region on the wing upper surface has a significant effect on the performance and transient response of small flying craft. The effect of free-stream turbulence on the separation region is not well documented.

To document the relative turbulence experienced by MAVs, a wide range of measurements were made in the Atmospheric Boundary Layer (ABL) using a set of dynamic multi-hole pressure probes mounted above a vehicle. The aim of the work was to understand the statistical characteristics of the turbulence, in terms of intensity and scale, and how these vary in different terrains and under different wind speeds. Using this information, a wind tunnel was setup to replicate the important aspects of this turbulent environment using grids.

A representative flat plate MAV wing model was pressure tapped, and a dynamic pressure measurement system was used to obtain mean Cp information and frequency information up to 2 kHz. Flow visualisation was used to provide further insight into the interpretation of pressure measurements and which flow phenomena they represented. It was found that at increased turbulence levels, the overall aerodynamic performance of the wing was improved in terms of maximum CL and L/D, and the incidence at which the wing stalled was increased from 6◦ to approximately 12 degrees. Surface pressure measurements showed that in the low turbulence conditions (less than 1.5%) above an incidence of 4 degrees a separation bubble existed on the suction surface at the leading edge with reattachment further downstream. As the incidence was increased the separation bubble grew in size (chord-wise) up to an incidence of 8 degrees, where the flow separated, and the wing was in the stalled condition. Dynamic (time-varying) pressure measurements showed this separation region to be unstable, forming and bursting periodically and uniformly along the span of the wing. Increasing the ambient turbulence level confined the separation bubble to near the leading edge and delayed stall. At higher turbulence levels, the amplitude of the periodic formation and bursting of a local separation bubble increased; however, the shedding remained periodic in nature.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Aerospace, Mechanical and Manufacturing Engineering
Keyword(s) MAV
micro air vehicle, turbulence
ABL
atmospheric
boundary
layer
wind tunnel
pressures
aerofoil
air foil
low Reynolds number
separation bubble
surface pressures
stall
delay
flat plate
finite wing
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Created: Fri, 21 Sep 2012, 10:46:04 EST by Kelly Duong
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