Browsing by Subject "Aerospace Engineering"

Now showing 1 - 3 of 3
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    Binary drop coalescence in liquids.
    (2009-05) Kim, Jungyong
    Experiments on binary drop collisions within an index-matched liquid were conducted for Weber numbers (We) of 1-50 and collision angles of 15-80° below the horizontal. Drop pairs of water/glycerin mixture were injected into silicone oil and, due to gravitational effects, traveled on downward trajectories before colliding. A dual-field high-speed PIV measurement system was employed to quantify drop trajectories and overall collision conditions while simultaneously examining detailed velocity fields near the collision interface. In the We range examined, for equal size drops, both rebounding and coalescing behavior occurred. The drops coalesced for We > 10 and rebounded for We < 10, and this boundary was found to be insensitive to collision angle. Coalescence was found to result from a combination of vortical flow within drops and strong drop deformation characteristic of higher We. Flow through the centers of opposing ring vortices, strengthened by drop deformation, enhanced drainage of the thin film in the impact region, leading to film rupture and coalescence. The collision angle affected the eventual location of film rupture, with the rupture location moving higher in the thin film region as the collision angle increased. The film rupture location correlated closely with the location of maximum downward velocity in the thin film. The time between collision and rupture increases with We until We = 30. For We > 30, the time decreases as We increases. Unequal size drop collisions with drop size ratios (Ds/DL) of 0.7 and 0.5 were also examined. Coalescence occurs above We* = 11 similar to equal size drops. As drop size ratio decreases, the intervening film deforms more. If the velocity ratio uL/us < 1, the deformed interface becomes flat before coalescence. The rupture location varies due to the asymmetry of the drops. As collision offset increases (B > 0), the film rupture time is shortened and mixing of the fluid from both drops is enhanced after coalescence. The presence of tracer particles in the intervening film does not affect the minimum Weber number for coalescence, but the film ruptures earlier compared with cases lacking tracer particles.
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    On the Effects of a Vortex Breaker on the Wake Meandering Characteristics of a Miniature Wind Turbine
    (2017-12-14) Storm, Noah J.
    This investigation sought to understand how the addition of a vortex breaker to the nacelle of a miniature wind turbine might disrupt, enhance, mitigate, or otherwise alter the meandering characteristics of the wake flow. Velocity measurements were taken in the wake of the turbine in a wind tunnel experiment, and analyzed with MATLAB and Microsoft Excel. Three vortex breakers were designed, and each of these cases was compared to the wind turbine with no nacelle additions. A decrease in mean streamwise wake velocity and appreciable shifts in the peak meandering frequency and intensity were observed. Peak spanwise frequencies were normalized by the mean wake velocity to compensate for effects due to increased drag on the turbine when the vortex breakers were added. This normalization is appropriate, as previous experiments have shown that wake meandering scales with the Strouhal Number (St = fD/U) for utility and small-scale turbines [1]. Meandering frequency variations between vortex breaker cases and the bare nacelle case were partially attenuated when analyzing Strouhal percent differences. This suggests that the alterations in the meandering characteristics were a combinatorial result of both increased nacelle drag and vortex interactions between the nacelle vortex and blade tip vortices.
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    U of M UAV Research Project
    (2012-04-18) Bauer, Grant
    The University of Minnesota’s UAV Research Group focuses on developing low-cost, open source avionics and software for unmanned aerial vehicles. For continued progress to be made, the existing electronics needed to be upgraded in order to increase the UAV’s flight capability. The previous avionics architecture lacked the capability to measure of the aircraft control surface positions. The goal of this UROP was to investigate the use of low-cost commercial-off-the-shelf (COTS) sensors to fill the aforementioned capability gap, followed by the integration, testing, and calibration of the sensors themselves. After successfully incorporating these sensors into the UAV’s avionics architecture, the plane is now able to transmit the angle of attack of each of its six control surfaces to the ground station in mid-flight. This then allows the research group to attain more accurate flight data from the plane and more easily detect anomalies, like servo faults, that disrupt the plane’s flight characteristics. Since the UAV Research Group has an open source policy, much of the progress made by the group as a whole will help enable widespread civilian use of UAV’s for applications like law enforcement, aerial photography and surveying, and atmospheric sensing.