Micro Air Vehicles are currently receiving growing interest because of their broad applications in many fields. However, in MA V flight tests, the onset of unwanted large-amplitude roll oscillations for various designs has been reported, which has eventually led to difficulties in flight control and such undesirable selfinduced roll oscillations were investigated in the current study. More specifically, a common low-aspect-ratio wing, an AR = 2 rectangular flat plate, was researched, with the aim being to attenuate the self-induced roll oscillation of low-aspect-ratio wings by applying various flow control techniques. These flow control techniques were applied using in three completely different approaches using three different flow control techniques, i) global active excitation, ii) local active excitation and iii) passive flow control. The global active excitation was achieved by using external acoustic forcing and it is found that the self-induced roll oscillations of AR = 2 flat plate wing can be completely suppressed as well as the onset of the roll oscillations delayed using this method. Similar results were also obtained for wings with airfoil profiles of NACA0012 and SD7003-085-88. In addition, the velocity measurements indicated that acoustic excitation could restore a symmetric vortex flow over the free-to-roll wings and thus eliminate the self-induced roll oscillations. Frequency spectral study revealed that acoustic excitation could energize the shear layer instabilities and result in reattachment or a smaller separated flow region over the suction surface of the wings, thereby, attenuating the roll oscillations.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:619294 |
| Date | January 2014 |
| Creators | Hu, Tianxiang |
| Publisher | University of Bath |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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