UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

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 given thesis/dissertation in DRUM.

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

Browse

Filters

2020 - 20222

Settings

Subject: search.filters.subject.aircraft

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    PERFORMANCE OF ELECTRIC MEDIUM-SIZED VARIABLE-RPM ROTOR AND SHROUDED ROTOR
    (2022) Ryseck, Peter Christian; Chopra, Inderjit; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Electric variable RPM rotors are increasingly being used for propulsion and control of unmanned air vehicles. As these vehicles scale to carry heavier payloads of 50 to 400 lbs (20 to 180 kgs) in the group 2 and 3 UAS category, there are concerns about their aerodynamic performance and handling quality degradation. Therefore, there is a need to develop a systematic experimental testing procedure to measure loads on these systems to evaluate performance and augment Computational Fluid Dynamic (CFD) validation tools. In this work, a universal electric powered test rig is designed and fabricated for hover and wind tunnel tests of open and shrouded rotors. Steady hover results are validated using blade element momentum theory. These predictions incorporate an empirical correction approach in conjunction with an interpolation scheme to capture Reynolds number variation along the span of the blade and variation with RPM. Results show good agreement with the interpolation method for the low Reynolds number rotor tested (Re_tip<500,000). For the variable RPM rotor, transient step and chirp inputs are also presented. System identification showed linear frequency responses between thrust and torque with RPM and RPM-square in hover. Therefore, when modeling this rotor, steady inflow appears adequate in the frequency range of interest (0.4 to 60 rad/sec). In addition to an open rotor, the electric motor-rotor test stand was used to test a shrouded rotor in hover and forward flight to systematically compare performance results. Test data showed the shrouded rotor gained 15% thrust for the same power in hover with the best configuration. For low speed forward flight, lift-to-drag ratio was found to increase by 8 to 10% for the shrouded rotor system over the isolated rotor.
  • Thumbnail Image
    Item
    EXAMINATION OF PHOTOCHEMISTRY AND METEOROLOGY OF ATMOSPHERIC POLLUTANTS FROM THE NORTH CHINA PLAIN
    (2020) Benish, Sarah Elizabeth; Dickerson, Russell R; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Increasingly severe air pollution over metropolitan regions in China has raised attention in light of its local and regional impacts on health and climate. Computer models can simulate complex interactions between photochemistry and meteorology to inform policy decisions in reducing ground-level pollution. However, models rely on an accurate portrayal of emissions that often possess large uncertainties over regions with evolving pollution characteristics. This work is comprised of a quantitative analysis of air pollutants in the North China Plain that strives to improve such uncertainties by identification of important sources and meteorological conditions for pollution through the combination of observations and models. Measurements used in this dissertation focus on in situ observations from the Spring 2016 Air chemistry Research in Asia (ARIAs) campaign, which sampled atmospheric composition across the heavily populated and industrialized Hebei Province in the North China Plain. High amounts of ozone (O3) precursors were found throughout and even above the planetary boundary layer, continuing to generate O3 at high rates to be potentially transported downwind. Evidence for the importance of anthropogenic VOCs on O3 production is presented. Concentrations of NOx and VOCs even in the rural areas of this highly industrialized province promote widespread O3 production and in order to improve air quality over Hebei, both NOx and VOCs should be regulated. The ARIAs airborne measurements also provide a critical opportunity to characterize chlorofluorocarbons (CFCs) over a suspected CFC-11 source region in China, finding mixing ratios were well above 2016 global background levels. Based on correlations of CFCs with compounds used in their manufacture, I identify likely source regions of new CFCs production and release, in violation of the Montreal Protocol. Finally, I examine the influence of meteorology on surface and aloft measurements during ARIAs. A multiday persistent high pressure episode is presented as a case study to examine the influence of regional transport on air quality measured during ARIAs. This dissertation provides valuable information for understanding one of the most polluted regions in China. Coordinated field and modeling efforts can together provide scientific guidance to inform pollution control measures to meet air quality targets in China.