A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Effect of Sloped Terrain on In-Ground-Effect Hover Performance for an Isolated Rotor(2023) Prewitt, Jack; Tritschler, John; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The present work conducted performance testing using a laboratory-scale isolated rotor operating over a ground plane mounted to a six degree-of-freedom motion platform to simulate in-ground-effect operations over sloped terrain. The rotor utilized a pair of 1:13.24 scale OH-58C blades, and performance measurements were collected using a six-axis load cell to which the rotor was mounted. Seven ground plane angles ranging from 0–18 deg, five collective blade pitches ranging from 0–8 deg, and 15 hub heights ranging from a nondimensional hub height, z/R, of 0.6 to 2.0 were tested. Additionally, the rotor was operated out-of-ground-effect for collective blade pitches ranging from 0–12 deg in increments of 1 deg in order to compare in-ground-effect and out-of-ground-effect hover performance. In-ground-effect hover over sloped terrain was found to have over a 7% reduction in performance as compared to hover over level terrain at low hub heights and large ground plane angles. In-ground-effect hover over sloped terrain was also found to require 2% more power than hover out-of-ground-effect at high hub heights and large ground plane angles. Finally, a semi-empirical model for hover performanceover sloped terrain was developed on the basis of the classic Cheeseman and Bennett ground effect model for level terrain. The coefficients obtained from this model were found to change in a consistent manner as both ground plane angle and blade loading coefficient changed, which suggests that the model could be used for future performance predictions for hover over sloped terrain.Item THERMAL HYDRAULIC CHARACTERIZATION AND VALIDATION OF HEAT EXCHANGERS BASED ON TRIPLY PERIODIC MINIMAL SURFACE(2021) Dharmalingam, Lalith Kannah; Aute, Vikrant C; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rapid growth in the field of additive manufacturing has set off a stream ofresearch into complex shapes and geometries for engineering applications. Triply Periodic Minimal Surfaces (TPMS) are a class of differential surfaces that are gaining such increased interest in the past few years. Of the most commonly studied TPMS, Schwarz-D TPMS has been shown to out-perform traditional Heat eXchanger (HX) designs in recent research. This research examines some of the under-studied TPMS structures for HX applications. Fischer-Koch S, C(Y), and C(±Y) TPMS structures were numerically analyzed to predict their thermal-hydraulic performance and the results were compared with a Schwarz-D TPMS HX. The under-studied TPMS HXs showed a 1.5 to 5 times increase in overall thermal performance while maintaining similar pressure drops when compared to the Schwarz-D TPMS HX. Furthermore, thermal-hydraulic characterization of a full-scale TPMS based HX design was carried out for high temperature (> 900 °C) applications and a parametric HX design solver was developed to predict its performance within ±5% deviation.Item Characterization and Modeling of Brushless DC Motors and Electronic Speed Controllers with a Dynamometer(2019) Brown, Robert; Chopra, Inderjit; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The global drone market is expected to grow from $4.9 billion to $14.3 billion within the next decade, indicating a heavy demand for high performance electric aircraft. Modern drones are propelled with brushless DC (BLDC) motors and electronic speed controllers (ESCs). However, a current lack of information concerning the performance and efficiency of BLDC motors and ESCs prevents their use in rigorous aircraft design. Low cost hobby ESCs and BLDCs are typically used in research aircraft, but few technical details are released by their manufacturers. To better understand these devices, a custom dynamometer was constructed to study the performance of ESCs and BLDC motors. By properly recording the DC, AC, and mechanical power, information on peak efficiency and performance for the ESCs and BLDC motors are determined experimentally. Motors between 920 KV to 2500 KV were tested with 18 A, 30 A, and 40 A ESCs. A combination of these tests were carried out at 7.2 V, 11.1 V, and 14.8 V DC to explore trade offs in the design process. While typically neglected in formal analysis, this work seeks to better understand the power loss mechanisms in ESCs, as it was found that ESCs could have efficiencies as low as 65%, reducing the overall efficiency of the system considerably. This custom dynamometer features a load varying device, power analyzers, and a unique two DAQ setup to properly capture the high frequency electrical signals of BLDC motors. From the sets of experimentally recorded motor and ESC tests, a novel analytical model is developed to predict the performance of ESCs and BLDC motors. At the heart of this modeling effort is describing the 3 phase AC circuit as a single equivalent circuit, which encapsulating the motor’s performance. This work is critical in the design process, as properly sizing ESCs, motors, and rotors for an electric aircraft can improve aircraft endurance and range. Performance metrics are extracted from experimental results and are fit into the analytical model. Predictions for the system’s mechanical power, AC power, and DC power agree well with experimental results, demonstrating applicability of the robust model.Item Design and Performance of a Ducted Coaxial Rotor in Hover and Forward Flight(2010) Lee, Timothy Edward; Leishman, J. Gordon; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A ducted contra-rotating coaxial rotor system was designed and tested to assess its potential use as a micro aerial vehicle (MAV). Performance measurements (thrust and power) of the system in hover and forward flight were obtained. The influence of several design parameters (rotor spacing, duct inlet shape, position of rotors within the duct, and tip clearance) on performance was determined. Performance measurements of the unducted coaxial rotor, as well as the unducted/ducted single rotor configurations, were also obtained to give a performance baseline for the ducted coaxial rotor. The aerodynamic characteristics of the isolated duct were assessed from loads measurement and surface flow visualization. While the net system performance of operating the coaxial rotor within the confines of a duct was not always improved, the ducted coaxial rotor concept is still attractive for a MAV based on total attainable thrust for a given rotor size and other operational benefits.Item Design and Performance Prediction of Swashplateless Helicopter Rotors with Trailing Edge Flaps and Tabs(2010) Falls, Jaye; Chopra, Inderjit; Datta, Anubhav; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work studies the design of trailing edge controls for swashplateless helicopter primary control, and examines the impact of those controls on the performance of the rotor. The objective is to develop a comprehensive aeroelastic analysis for swashplateless rotors in steady level flight. The two key issues to be solved for this swashplateless control concept are actuation of the trailing edge controls and evaluating the performance of the swashplateless rotor compared to conventionally controlled helicopters. Solving the first requires simultaneous minimization of trailing flap control angles and hinge moments to reduce actuation power. The second issue requires not only the accurate assessment of swashplateless rotor power, but also similar or improved performance compared to conventional rotors. The analysis consists of two major parts, the structural model and the aerodynamic model. The inertial contributions of the trailing edge flap and tab are derived and added to the system equations in the structural model. Two different aerodynamic models are used in the analysis, a quasi-steady thin airfoil theory that includes arbitrary hinge positions for the flap and the tab, and an unsteady lifting line model with airfoil table lookup based on wind tunnel test data and computational fluid dynamics simulation. The predicted swashplateless rotor power is sensitive to the pattern of trailed vorticity from the rotor blade. Trailed vortices are added at the inboard and outboard boundaries of the trailing edge flap, and the flap deflection is used to calculate an effective angle of attack for the calculation of the near and far wake. This wake model predicts the swashplateless rotor requires less main rotor power than the conventional UH-60A helicopter from hover to &mu = 0.25. As the forward flight speed increases, the swashplateless predicted power increases above the conventional rotor, and the rotor lift-to-drag ratio decreases below that of the conventional rotor.