Extensions of Fundamental Flow Physics to Practical MAV Aerodynamics
Abstract
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.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 2016
- Accession Number
- AD1016711
Entities
Organizations
- NATO Science and Technology Organization