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An Experimental Study of Static and Oscillating Rotor Blade Sections in Reverse Flow

dc.contributor.advisorJones, Anya Ren_US
dc.contributor.authorLind, Andrew Humeen_US
dc.date.accessioned2016-02-09T06:33:53Z
dc.date.available2016-02-09T06:33:53Z
dc.date.issued2015en_US
dc.identifierhttps://doi.org/10.13016/M22M8H
dc.identifier.urihttp://hdl.handle.net/1903/17361
dc.description.abstractThe rotorcraft community has a growing interest in the development of high-speed helicopters to replace outdated fleets. One barrier to the design of such helicopters is the lack of understanding of the aerodynamic behavior of retreating rotor blades in the reverse flow region. This work considers two fundamental models of this complex unsteady flow regime: static and oscillating (i.e., pitching) airfoils in reverse flow. Wind tunnel tests have been performed at the University of Maryland (UMD) and the United States Naval Academy (USNA). Four rotor blade sections are considered: two featuring a sharp geometric trailing edge (NACA 0012 and NACA 0024) and two featuring a blunt geometric trailing edge (ellipse and cambered ellipse). Static airfoil experiments were performed at angles of attack through 180 deg and Reynolds numbers up to one million, representative of the conditions found in the reverse flow region of a full-scale high-speed helicopter. Time-resolved velocity field measurements were used to identify three unsteady flow regimes: slender body vortex shedding, turbulent wake, and deep stall vortex shedding. Unsteady airloads were measured in these three regimes using unsteady pressure transducers. The magnitude of the unsteady airloads is high in the turbulent wake regime when the separated shear layer is close to the airfoil surface and in deep stall due to periodic vortex-induced flow. Oscillating airfoil experiments were performed on a NACA 0012 and cambered ellipse to investigate reverse flow dynamic stall characteristics by modeling cyclic pitching kinematics. The parameter space spanned three Reynolds numbers (165,000; 330,000; and 500,000), five reduced frequencies between 0.100 and 0.511, three mean pitch angles (5,10, and 15 deg), and two pitch amplitudes (5 deg and 10 deg). The sharp aerodynamic leading edge of the NACA 0012 airfoil forces flow separation resulting in deep dynamic stall. The number of associated vortex structures depends strongly on pitching kinematics. The cambered ellipse exhibits light reverse flow dynamic stall for a wide range of pitching kinematics. Deep dynamic stall over the cambered ellipse airfoil is observed for high mean pitch angles and pitch amplitudes. The detailed results and analysis in this work contributes to the development of a new generation of high-speed helicopters.en_US
dc.language.isoenen_US
dc.titleAn Experimental Study of Static and Oscillating Rotor Blade Sections in Reverse Flowen_US
dc.typeDissertationen_US
dc.contributor.publisherDigital Repository at the University of Marylanden_US
dc.contributor.publisherUniversity of Maryland (College Park, Md.)en_US
dc.contributor.departmentAerospace Engineeringen_US
dc.subject.pqcontrolledAerospace engineeringen_US
dc.subject.pqcontrolledEngineeringen_US
dc.subject.pquncontrolledDynamic Stallen_US
dc.subject.pquncontrolledExperimentalen_US
dc.subject.pquncontrolledHelicoptersen_US
dc.subject.pquncontrolledReverse Flowen_US
dc.subject.pquncontrolledUnsteady Aerodynamicsen_US


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