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
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Item CFD/CSD STUDY OF INTERACTIONAL AERODYNAMICS OF A COAXIAL COMPOUND HELICOPTER IN HIGH-SPEED FORWARD FLIGHT(2020) Klimchenko, Vera; Baeder, James; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work presents a computational study of the aerodynamic interactions that arise between the components of a high-speed lift-offset coaxial compound helicopter in forward flight. The objective of this study is to develop a computational methodology that would enable fundamental understanding of the complex aeromechanics of a modern lift-offset coaxial compound rotorcraft configuration in it's entirety. The modeling of a helicopter is a coupled aeroelastic problem, in which the aerodynamics is highly dependent on the structural dynamics, and vice versa. Therefore, the prediction of the rotorcraft airloads and blade deformations must be performed with sufficient fidelity to accurately model both aspects of the problem. A high-fidelity computational fluid dynamics framework, HPCMP CREATE$^{TM}$-AV Helios, was used in conjunction with an in-house comprehensive analysis solver, to simulate a lift-offset coaxial compound helicopter in forward flight. A notional X2TD helicopter consisting of a lift-offset coaxial rotor, airframe and an aft-mounted propeller, was modeled in this work. An in-house comprehensive analysis solver, PRASADUM, performed trim calculations and the structural modeling using low order aerodynamics. Conventionally, the comprehensive analysis rotor airloads that are computed from the built-in low order aerodynamic models, would be corrected with the high-fidelity CFD airloads using delta coupling procedure. In this study, the conventional rotor delta coupling methodology was used to study the interactional aerodynamics of a coaxial rotor system in forward flight at a range of flight speeds (50 knots to 225 knots). This study also focused on extending this methodology to perform high-fidelity airloads corrections for airframe and the propeller. The low order rotor, airframe and propeller aerodynamic loads were corrected with the high-fidelity CFD airloads, using a full vehicle loose delta coupling methodology. The two CFD/CSD coupling approaches, rotor and full vehicle, were compared. The results showed that correcting the low fidelity CSD airframe airloads with high-fidelity CFD airloads affects the rotor trim solution. The converged trim state from the full vehicle delta coupling procedure was utilized to study the fundamental interactional aerodynamics between various components of the coaxial compound helicopter. The CFD simulations were performed for isolated helicopter components and component combinations.Item Aeromechanics of a High Speed Coaxial Helicopter Rotor(2017) Schmaus, Joseph Henry; Chopra, Inderjit; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The current work seeks to understand the aeromechanics of lift offset coaxial rotors in high speeds. Future rotorcraft will need to travel significantly faster that modern rotorcraft do while maintaining hovering efficiency and low speed maneuverability. The lift offset coaxial rotor has been shown to have those capabilities. A majority of existing coaxial research is focused on hovering performance, and few studies examine the forward flight performance of a coaxial rotor with lift offset. There are even fewer studies of a single rotor with lift offset. The current study used comprehensive analysis and a new set of wind tunnel experiments to explore the aeromechanics of a lift offset coaxial rotor in high speed forward flight. The simulation was expanded from UMARC to simultaneously solve multiple rotors with coupled aerodynamics. It also had several modifications to improve the aerodynamics of the near-wake model in reverse flow and improve the modeling of blade passages. Existing coaxial hovering tests and flight test data from the XH-59A were used to validate the steady performance and blade loads of the comprehensive analysis. It was used to design the structural layout of the blades used in the wind tunnel experiment as well as the test envelope and testing procedure. The wind tunnel test of a model rotor developed by the University of Texas at Austin and the University of Maryland was performed in the Glenn L Martin Wind Tunnel. The test envelope included advance ratios 0.21–0.53, collectives 4◦– 8◦, and lift offsets 0%–20% for both rotors tested in isolation and as a coaxial system operating at 900 RPM. Rotating frame hub loads, pushrod loads, and pitch angle were recorded independently for each rotor. Additional studies were performed at 1200 RPM to isolate Reynold effects and with varying rotor-to-rotor phase to help quantify aerodynamic interactions. Lift offset fundamentally changes the lift distribution around the rotor disk, doing so increases the maximum thrust of the rotor at a given speed while at the same time increasing the rotor efficiency. The cost of lift offset is increased blade loads. While this can be seen in the experimental data, it was taken at constant collective and as lift offset increased so did the thrust. The simulation is used to provide performance and loads sweeps at constant thrust to help provide a more basic understanding of how the rotor performance is changing. Additionally, rotor thrust and drag distributions provide a physical insight on how the distribution of lift changes cause the resulting trends that have been observed. Coaxial rotors have been shown to have significant rotor-to-rotor interactions in hover, but the magnitude of those interactions at high speed are studied here in detail. Generally, the aerodynamic interactions decrease significantly with increasing speed, and finally the lower rotor wake convects off the upper rotor. A comparison between the single rotor and coaxial rotor performance shows a newly observed trend of thrust inversion, where the more efficient rotor changes from the top in hover to the bottom in forward flight. The vibratory loads show limited evident of direct coaxial interference, although it is shown that the relative phase of the two rotors significantly alters the resultant total loads.