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Parameter Studies on Rotational and Translational Accelerations of Flat Plates

Abstract : We compare a broad range of transient translations, and a smaller collection of transient rotations, of flat plates of aspect ratio 2, 4, and nominally 2D, tracking lift and drag coefficients vs. motion history, for a range of acceleration profiles and motion modalities, and for Reynolds numbers from 14 through 10,000. Kinematics include a translational acceleration, consisting of a linear ramp in velocity vs. convective time, starting from rest and with fixed incidence angle; a pitch about various chordwise pivot points in constant free-stream; a combination of the two, with both pitch and translational acceleration; a plunging motion in steady free stream; and finally, a rotational acceleration, where the plate is again initially at rest and accelerates azimuthally to some steady rotational speed. Accelerations cover reduced frequencies from K = pi/48 to pi/4. Noncirculatory loads vary as the square of the reduced frequency, and are particularly pronounced during smoothing-transients applied to linear ramps. For the cases of pitching and combined pitching and translational acceleration, moving the pitch pivot point aft delays leading edge vortex production and attenuates lift. At Re = 10,000 lift and drag histories are essentially identical for the translational acceleration case. The same is true for the rotational acceleration case, implying that the net aerodynamic force is wall-normal.While we do not presently aspire to comprehensive reconciliation of the extant literature, the aim is to build a large parameter-library of cases using comparatively topical techniques (direct force measurement and flow visualization by dye injection) to compare translational and rotational motions, to then prompt deeper study of a few expository cases. The work is part of the NATO AVT-202 Task Group, Extension of Fundamental Flow Physics for Practical MAV Aerodynamics , and as such aims towards basis for computational validation and investigation of experimental parameters.