Aerospace Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2737
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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 Measurement and Scaling Analysis of Rotor-Induced Sediment Mobilization(2014) Perrotta, Gino; Jones, Anya; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Flow visualization and particle imaging velocimetry (PIV) experiments were conducted in a water tank to investigate the effects of rotor wake and sediment properties on rotor-induced sediment mobilization during hover in ground effect. The two-phase flow was separated into the carrier phase and the dispersed phase for characterization. The carrier phase was studied using PIV to acquire time-resolved planar velocity measurements for a field of view within the rotor wake. The rotor-induced flow was confirmed to be dominated by blade tip vortices and was characterized primarily in terms of the vortex characteristics. Vortices were identified using a tracking function, and were compared to the Lamb-Oseen vortex velocity profile to evaluate their size and strength. The rotor-induced flow was also characterized in terms of wall-jet velocity and turbulent kinetic energy. The dispersed phase was separated using image filtering procedures and was quantified by identifying mobilized sediment particles visible in the field of view. Characteristics of the rotor-induced flow and quantification of sediment mobilization were each averaged over time for several rotor rotations to reduce the effects of wake aperiodicity and asymmetry. New parameter groups were created by combining rotor-induced sediment mobilization system characteristics and each was inspected for correlation with sediment mobilization. Three parameter groups which correlated for all cases measure here are identified and discussed.