Aerospace Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2737
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Item Investigation into the Aerodynamics of Swashplateless Rotors Using CFD-CSD Analysis(2012) Jose, Arun Isaac; Baeder, James D; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study obtains a better understanding of the aerodynamics of integrated trailing edge flap (TEF) based swashplateless rotors. Both two dimensional (2D) and three dimensional (3D) analysis/simulations are performed to understand the behavior of TEF airfoils and integrated TEF based swashplateless rotors. The 2D aerodynamics of TEF airfoils is explored in detail. A semi-empirical approach is developed for modeling drag for TEF airfoils in steady flows based on baseline airfoil drag data alone. Extensive 2D CFD simulations are performed for a wide range of flow conditions in order to better understand various aspects of the aerodynamics of TEF airfoils. The trends in the airloads (lift, drag, pitching moment, hinge moment) for TEF airfoils are obtained. Nonlinear phenomena such as flow separation, shocks and unsteady vortex shedding are investigated, and the flow conditions and trends associated with them are studied. The effect of airfoil properties such as thickness and overhang are studied. Various approaches are used to model the effect of gaps at the leading edge of the flap. An approximate ``gap averaging'' technique is developed, which provides good predictions of steady airloads at almost the same computational cost as a simulation where the gap is not modeled. Direct modeling of the gap is done by using a patched mesh in the gap region. To solve problems (such as poor grid quality/control and poor convergence) that are associated with the patched mesh simulations, an alternate approach using overlapping meshes is used. It is seen that for TEF airfoils, the presence of gaps adversely affects the effectiveness of the flap. The change in airloads is not negligible, especially at the relatively higher flap deflections associated with swashplateless TEF rotors. Finally, uncoupled and coupled computational fluid/structural dynamics (CFD-CSD) simulations of conventional (baseline) and swashplateless TEF rotors is performed in hovering flight. The CFD-CSD code is validated against experiment and good agreement is observed. It is observed that the baseline UH-60 rotor performs better than the swashplateless UH-60 rotor. For an untwisted NACA0012 airfoil based rotor, the performance is similar for the baseline and swashplateless configurations. The effect of gaps on the performance of swashplateless TEF rotors is also investigated. It is seen that the presence of chordwise gaps significantly affects the effectiveness of the TEF to control the rotor. Spanwise gaps also affect the performance of swashplateless rotors but their effect is not as significant.Item Unsteady Aerodynamic Modeling With Time-Varying Free-Stream Mach Numbers(2005-12-02) Jose, Arun Isaac; Leishman, John G; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The development of a reduced-order unsteady airfoil theory is described for application to non-steady, subsonic compressible flows with variable free-stream Mach number. The airfoil theory, which is suitable for application to most types of comprehensive helicopter rotor analyses, is developed for arbitrary, time-dependent combined variations in angle of attack and Mach number. The approach is validated using CFD solutions based on the Euler equations. The new model is developed using the indicial theory as a basis, and shows excellent agreement with direct CFD solutions for a wide range of practical flows. For supercritical flows, nonlinearities associated with the formation and movement of shock waves are observed in the CFD solutions, which the unsteady airfoil theory proves inadequate. Overall, this study shows that the reduced-order unsteady aerodynamic theory provides significant improvements in sectional airloads predictions over existing methods that might be used in various types of comprehensive helicopter rotor analyses.