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.
Browse
2 results
Search Results
Item FUNDAMENTAL UNDERSTANDING OF HELICOPTER AEROMECHANICS ON MARS THROUGH CHAMBER TESTING AND HIGH-FIDELITY ANALYSIS(2020) Escobar, Daniel; Datta, Anubhav; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The fundamental aeromechanics of rotary-wing flight on Mars is explored. The exploration is based on chamber testing of Mars-like low Reynolds number rotors and the development of comprehensive analysis and comprehensive analysis coupled with computational fluid dynamics for systematic investigation of aeromechanical phenomena--critical for weights and packaging for Mars. The investigation includes rotor airloads, structural loads, and control loads, comparison of hingeless and articulated hubs, hover and forward flight, and the impact of fuselage aerodynamics. The coaxial configuration is the baseline platform for this work. The use of a helicopter on Mars would dramatically increase the speed, range, and coverage of exploration by providing access to caves, craters, over polar ice, along icy scarps and recurring slope lineae that are just plain inaccessible or too dangerous for rovers. Many factors go into the design of a Mars helicopter from launch/entry loads to power to controls to packaging. Aeromechanics is only one factor, but the principal factor for efficient and effective flight that impacts everything else. This work is focused on this principal factor. Current knowledge extrapolated from Earth would allow for short hops into the Mars atmosphere. Deeper understanding of Martian aeromechanics is needed to design larger more capable aircraft. Accurate predictions are needed for performance, blade loads, control loads, and blade strike behavior. True high-fidelity is needed for unlike on Earth decades of data sets do not exist on Mars. In fact there is not even a single data set. Thus clever and innovative means of verification and validation must be found. The objective of this thesis is to carry out all of these tasks. The key conclusions are: (1) the design of aircraft, hub, blades, and controls are substantially different on Mars because of its unique aeromechanics, (2) an articulated hub can in fact have lesser danger of blade strike, (2) a hingeless hub can experience lower or only marginally higher (6-7%) flap bending moments, (3) control / pitch link loads are dramatically impacted more by choice of Mars airfoils than rotor hubs, (4) lifting-line analysis does not even begin to capture the precise magnitudes of blade passage impulsive loads, and (5) fuselage aerodynamics is irrelevant in preliminary design. These, and other interesting phenomena will be the topics of this dissertation.Item Morphing Waveriders for Atmospheric Entry(2019) Maxwell, Jesse R; Oran, Elaine S; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The primary challenge for vehicles entering planetary atmospheres is surviving the intense heating and deceleration encountered during the entry process. Entry capsules use sacrificial ablative heat shields and sustain several g deceleration. The high lift produced by the Space Shuttle geometry resulted in lower rates of heating and deceleration. This enabled a fully reusable vehicle that was protected by heat shield tiles. Hypersonic waveriders are vehicles that conform to the shape of the shock wave created by the vehicle. This produces high compression-lift and low drag, but only around a design Mach number. Atmospheric entry can reach speeds from zero to as high as Mach 40. A morphing waverider is a vehicle that deflects its flexible bottom surface as a function of Mach number in order to preserve a desired shock wave shape. It was demonstrated in this work that doing so retains high aerodynamic lift and lift-to-drag ratio across a wide range of Mach number. Numerical simulations were conducted for case-study waveriders designed for Mach 6 and 8 for flight at their design conditions as well as with variations in angle-of-attack and Mach number. A single-species air model was used between Mach 1 and 12 with the RANS k-omega SST and LES-WALE turbulence models. A seven-species air model was used for Mach 15 at 60km altitude and Mach 20 at 75km. Analytical methods were used to construct a reduced-order model (ROM) for estimating waverider aerodynamic forces, moments, and heating. The ROM matched numerical simulation results within 5-10% for morphing waveriders with variations in angle-of-attack, but discrepancies exceeded 20% for large deviations of rigid vehicles from their design Mach numbers. Atmospheric entry trajectory simulations were conducted using reduced-order models for morphing waverider aerodynamics, the Mars Science Laboratory (MSL) capsule, and the Space Shuttle. Three morphing waveriders were compared to the Space Shuttle, which resulted in reduced heating and peak deceleration. One morphing waverider was compared to the MSL capsule, which demonstrated a reduction in the peak stagnation heat flux, a reduction in the peak and average deceleration, and a reduction in the peak area-averaged heating.