Extensions of Fundamental Flow Physics to Practical MAV Aerodynamics
NATO SCIENCE AND TECHNOLOGY ORGANIZATION NEUILLY-SUR-SEINE (FRANCE) NEUILLY-SUR-SEINE France
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In massively unsteady wing-flows, organized flow-separation may increase lift well above steady-state. We explore imposed rotations and rectilinear translations of rigid flat plates in incompressible flow, comparing a linear-ramp angle of attack change with streamwise acceleration surge. In rotation, the plate revolves about an axis inboard of its inboard tip, notionally representative of a flapping-wing. Experiment, computation and analysis culminated in a two-dimensional lumped vortex model for physics-based accounting of lift history. Rotation was found to stabilize the leading edge vortex, at least for inboard spanwise locations the vortex sheds after saturation for the translational case. However, no advantage in peak lift or lift to drag ratio was found in rotation during the manoeuvre itself. Pitching causes a large force transient, both for rotation and translation, relative to surging this is due to pitch-rate effects, predicted by unsteady aerofoil theory, which also accurately handles apparent-mass effects. For translation, 10 convective times are needed for the post-manoeuvre lift transient to relax the rotational case reaches a steady lift value in roughly 5 convective times, and this steady value is higher than for translation. Thus rotation offers a steady-state advantage in lift, but not a transient one, owing to leading-edge vortex behaviour.
- Fluid Mechanics
- Pilotless Aircraft