Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

Browse

Filters

20172

Settings

Subject: search.filters.subject.high speed

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Refined Performance and Loads of a Mach-Scale Rotor at High Advance Ratios
    (2017) Trollinger, Lauren Nicole; Chopra, Inderjit; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This work will investigate the performance and vibratory loads of a Mach-scale rotor with highly similar, non-instrumented blades at advance ratios (µ) up to 0.9. Wind tunnel tests were performed on a 4-bladed, articulated rotor with a diameter of 2.78 ft. The slowed rotor was operated at 30%, 40%, and 50% of nominal speed,corresponding to advancing tip Mach numbers up to 0.53, and shaft tilt angles of -4◦, 0◦, and 4◦ were tested. Collective sweeps from -2◦ to 12◦ were performed for each flight condition, and blade motion, control cyclics, and hub loads were measured. Blade similarity was shown to improve rotor track and trim at high µ. Thrust reversal was observed at µ = 0.9, but positive (aft) shaft tilt increased lift at high µ. Vibratory hubloads are shown to increase with advance ratio. Correlations performed using the comprehensive analysis code UMARC show good agreement for rotor performance.
  • Thumbnail Image
    Item
    Magnetorheological fluid dynamics for high speed energy absorbers
    (2017) Sherman, Stephen Gilman; Wereley, Norman M; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Fluids with a controllable yield stress allow rapid variations in viscous force in response to an externally applied field. These fluids are used in adaptive energy dissipating devices, which have a controllable force response, reducing shock and vibration loads on occupants and structures. This thesis investigates the physics of these fluids at high speeds and shear rates, through particle modeling and fluid dynamics. The focus is on the experimentally observed reduction in controllable force at high speeds seen in magnetorheological (MR) fluid, a suspension of magnetizable particles that develop a yield stress when a magnetic field is applied. After ruling out particle dynamic effects, this dissertation takes the first rigorous look at the fluid dynamics of a controllable yield stress fluid entering an active region. A simplified model of the flow is developed and, using computational fluid dynamics to inform a control volume analysis, we show that the reduction in high speed controllable force is caused by fluid dynamics. The control volume analysis provides a rigorous criteria for the onset of high speed force effects, based purely on nondimensional fluid quantities. Fits for pressure loss in the simplified flow are constructed, allowing yield force prediction in arbitrary flow mode geometries. The fits are experimentally validated by accurately predicting yield force in all of the known high speed devices. These results should enable the design of a next generation of high performance adaptive energy absorbers.