Abstract:SUMMARYThe aerodynamic force and flow structure of a wing performing an unsteady motion at small Reynolds number (Re = 4000) is calculated by solving Navier-Stokes equations. Calculations were conducted for steady motion, simple unsteady motions suc as azimuth rotation, pure translation, feathering, etc., which can provide a basis for understanding the more complicated hovering flight. At Re = 4000, the delayed stall mechanism was noted during the azimuth rotation of a wing due to span wise flow. In azimuth ro… Show more
“…From Table 1, the maximum lift is 8.59×10 −6 N. So the beetle does not meet the flight conditions. This findings conform to the findings of other studies on flying under steady flow condition at low Reynolds number range [27,37] . Wootton [12] suggested that the flying capabilities and various flight skills of insects are mostly due to that there are various wing types and complex wing movement patterns.…”
Section: Flight Simulation Of Beetle At Quasi-steady Statesupporting
The University of Gloucestershire accepts no liability for any infringement of intellectual property rights in any material deposited but will remove such material from public view pending investigation in the event of an allegation of any such infringement.
“…From Table 1, the maximum lift is 8.59×10 −6 N. So the beetle does not meet the flight conditions. This findings conform to the findings of other studies on flying under steady flow condition at low Reynolds number range [27,37] . Wootton [12] suggested that the flying capabilities and various flight skills of insects are mostly due to that there are various wing types and complex wing movement patterns.…”
Section: Flight Simulation Of Beetle At Quasi-steady Statesupporting
The University of Gloucestershire accepts no liability for any infringement of intellectual property rights in any material deposited but will remove such material from public view pending investigation in the event of an allegation of any such infringement.
“…Since stronger positive vorticity layers exist at the trailing edge of the cross sections at 31.26°↑ compared to 38.36°↑, this has caused the higher rate of lift coefficient at 31.26°↑ (Figure 9). 20 Figure 9.Contours of vorticity at Re = 10,000; (a) mean angle of attack = 24° and the angle 31.26°↑, (b) mean angle of attack = 30° and the angle 38.36°↑.…”
In this research, the flow physics and aerodynamic performance of dragonfly cross sections, used in Micro Aerial Vehicles (MAVs), in low Reynolds are investigated. The main objective of the research is to study the performance of dragonfly wing cross-sections flapping motion in Reynolds 5000 and 10,000. Pitching motion is one of the most important mechanisms in force lifting generation, and the effects of Reynolds number and mean angle of attack on aerodynamic coefficients have been extensively investigated for the pitching motion. In the present study, the geometry of two cross sections of dragonfly was extracted. Incompressible, two-dimensional and unsteady Navier–Stokes equations have been used to simulate the flow. k − ɛ RNG model was used for turbulence modeling. To simulate the wing pitching motion, the dynamic mesh method was used. The results showed that in flapping motion, pitching-up rotation has caused a rapid increase in lift coefficient. Furthermore, it was found that the absence of stall does not increase the lift and drag coefficients, while formation of new strong vorticity layers have caused an increase in lift coefficient. On the other hand, corrugations on the cross sections of the dragonfly in the pitching motion cause the delay of separation and increasing the lift coefficient. In flapping motion and the pitching motion, the lift coefficients of three cross sections were increased due to stronger vorticity layers by reducing the Reynolds number. Due to the existence of corrugations, the first and the second cross sections have good aerodynamic performance, compared to the flat plate. The comparison carried out in the current research showed that the second cross section is a proper replacement for the flat plate in MAVs.
“…The wing starts from rest in still air and achieves a constant angular velocity after moving through an azimuth angle of 20˚. It is worth mentioning that the duration of the acceleration phase is immaterial in the context of the delayed stall, as confirmed by Hamdani and Naqvi (2010).…”
Delayed stall is the most dominant lift enhancing factor in insect flapping motion. Micro air vehicle operates at Reynolds number 10 4 -10 5 ; slightly higher than the insects' Reynolds number (Re). In the present research, thefocus is to investigate "stall-absent" phenomenon at Re representative of the micro air vehicles, the effect of spanwiseflow on the leading edge vortex and also to study the effect of geometry variations on the aerodynamic performance of the wing in unsteady motion. Corrugated dragonfly airfoil with rectangular wing planform is used, however, with wing kinematics restricted to azimuth rotation only. Three-dimensionalfinitevolume method is used, through commercial software Fluent, to numerically solve time-dependent incompressible Navier-Stokes equations. Computed results at Re 34000 and 100,000 reveal the same phenomenon of delayed stall, as observed in the case of insects. Furthermore, the performance of flat plate, profiled and corrugated wing in a sweeping motion at a high angle of attack is also compared.
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