Aerospace Engineering
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Item Unsteady force production on a flat plate wing by large transverse gusts and plunging maneuvers(2017) Perrotta, Gino; Jones, Anya R; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The transient forces produced by large-amplitude transverse gust encounters and plunge maneuvers were studied experimentally in a water-filled towing tank. Forces were measured as a flat plate wing with an aspect ratio of four was towed through a fluid gust and as the same wing performed plunge maneuvers which matched the shape of the gust velocity profile. The transient velocity in each case conformed to the sine-squared profile, and the peak transient velocities were of the same order of magnitude as the steady towing velocities. In most cases, the wing pitch angle was high enough to cause constant flow separation. Even at low wing pitch angles, the increase in flow incidence angle by the transverse gust or plunge velocity was enough to cause flow separation. Transient force magnitudes were shown to increase with increasing stream-normal velocity for both the gust encounters and plunge maneuvers. Transient forces varied with increasing wing pitch angle during gust encounters but not during plunge maneuvers. Force histories in each case were compared to predictions made by existing small-perturbation force models, and adaptations were made to those models based on physical interpretation of the observed characteristics. Measured forces in both the gust encounters and the plunge maneuvers were found to correspond more closely to predictions made based on attached flow than on separated flow, which supports the suggestion that the presence of a leading edge vortex significantly augments the transient lift. Additionally, a large trailing edge vortex forms at the end of the gust encounter which temporarily reduces the force production below the steady-state values. This was not observed in the plunge maneuver force histories, which were much closer to quasi-steady than were the gust encounter force histories. This analysis contributes to the understanding of unsteady force production in large-amplitude events, and in particular in conditions with separated flow, the behaviors of which are not adequately captured by existing small-perturbation models.Item Photogrammetric Reconstruction of Tandem-Wing Kinematics for Free-Flying Dragonflies Undergoing a Range of Flight Maneuvers(2017) Gabryszuk, Mateusz; Laurence, Stuart J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Photogrammetric methods are used to reconstruct the body and wing kinematics of free-flying dragonflies. A novel experimental setup was designed and constructed to allow for repeated untethered flights in a constrained flight arena. Kinematic data are presented for twelve individual flights and a total of 23 complete wing strokes, including unaccelerating, accelerating, climbing, and turning flight. High variability is observed in the wing motions employed by individual dragonflies, particularly in terms of stroke amplitude, pitch angle, and wingbeat frequency. Forewing and hindwing flapping is found to be neither in phase nor fully out of phase across all cases, with the forewings lagging the hindwings by an average of 90 degrees. Downstroke durations are observed to be shorter than upstroke durations except in highly accelerating flights. Migratory dragonflies are found to exhibit notably different wing kinematics than non-migratory species.Item AN INVESTIGATION OF A MAV-SCALE FLEXIBLE FLAPPING WING IN FORWARD FLIGHT: FLOW FIELD AND AIRLOADS EXPERIMENTS WITH COUPLED CFD-CSD(2014) Mayo, David Benjamin; Chopra, Inderjit; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Experiments were systematically executed with a coupled computational fluid/structural dynamics aeroelastic analysis for a micro air vehicle scale flexible flapping-wing undergoing pure flap wing kinematics in forward flight. 2-D time-resolved particle image velocimetry and force measurements were performed in a wind tunnel where the free stream velocity was set to 3 m/s, Re = 15,000. Chordwise velocity fields were obtained at equally spaced spanwise sections along the wing (30% to 90% span) at the mid-downstroke and mid-upstroke of the flap cycle. The flowfield measurements and averaged force measurements were used for the validation of the 3-D aeroelastic model. The computational fluid/structural dynamics analysis combined a compressible Reynolds Averaged Navier Stokes solver with a multi-body structural solver. The objective of the combined efforts was to understand the force production of a flexible wing undergoing an avian-type flapping motion. The temporal and spanwise variation of wing pitch angle affected lift and drag, and primarily aided in producing positive thrust during both upstroke and downstroke.