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  • 1
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    Unsteady Airfoils (1982)
    Annual Reviews
    Details
    Publikationsdatum: 1982-01-01
    Print ISSN: 0066-4189
    Digitale ISSN: 1545-4479
    Thema: Maschinenbau , Physik
    Publiziert von Annual Reviews
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
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    Oscillating flow over a cylinder at large Reynolds number (1973)
    Cambridge University Press
    Details
    Publikationsdatum: 1973-12-18
    Beschreibung: The boundary-layer flow over a circular cylinder at a Reynolds number of 1·06 × 105 has been studied both experimentally and theoretically. The investigation was designed to concentrate on the self-induced oscillations occurring in the flow; at this Reynolds number, these oscillations have generally been ignored heretofore. In the experimental part of the investigation both the inviscid flow and boundary-layer flow reversals were measured as functions of time. The theoretical part of the study started with the measured inviscid flow and calculated all the boundary-layer characteristics. The boundary-layer calculations themselves revealed some very interesting fine-scale structure of the flow, which strongly indicated that the vanishing of wall shear does not signal the onset of separation for unsteady flow. In general, the agreement between the theoretical calculations and the experimental results was excellent and the unsteady component of this supposedly steady flow was found to be very significant. © 1973, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Digitale ISSN: 1469-7645
    Thema: Maschinenbau , Physik
    Publiziert von Cambridge University Press
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  • 3
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    Numerical solutions of forward-flight rotor flow using an upwind method (1991)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 28; 374-380
    Format: text
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  • 4
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    Acoustic propagation using computational fluid dynamics (1986)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-19
    Beschreibung: The propagation characteristics of several helicopter airfoil profiles have been investigated using the transonic small disturbance equation. A test case was performed to generate a moving shock that propagated off the airfoil. Various grids were then examined to determine their ability to accurately capture these propagating shock waves. Finally, the case of airfoil-vortex interactions was thoroughly studied over a wide range of Mach numbers and airfoil shapes with particular emphasis on the transonic regime; this results in a highly conplicated fluctuation of lift, drag, and pitching moment. The calculated acoustic intensity levels, along with the details of the computational flow field, provide new insights into the understanding of transonic airfoil-vortex interactions.
    Schlagwort(e): AERODYNAMICS
    Format: text
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  • 5
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    Airloads on bluff bodies, with application to the rotor-induced downloads on tilt-rotor aircraft (1985)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-19
    Beschreibung: The aerodynamic characteristics of airfoils with several flap configurations were studied theoretically and experimentally in environments that simulate a wing immersed in the downwash of a hovering rotor. Special techniques were developed for correcting and validating the wind tunnel data for large blockage effects, and the test results were used to evaluate two modern blockage effects, and the test results were used to evaluate two modern computational aerodynamics codes. The combined computed and measured results show that improved flap and leading-edge configurations can be designed which will achieve large reductions in the downloads of tilt-rotor aircraft, and thereby improve their hover efficiency.
    Schlagwort(e): AERODYNAMICS
    Materialart: Vertica (ISSN 0360-5450); 9; 1, 19; 1-11
    Format: text
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  • 6
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    The development of CFD methods for rotor applications (1988)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: The optimum design of the advancing helicopter rotor for high-speed forward flight always involves a tradeoff between transonic and stall limitations. However, the preoccupation of the rotor industry was primarily concerned with stall until well into the 1970s. This emphasis on stall resulted from the prevalent use of low-solidity rotors with rather outdated airfoil sections. The use of cambered airfoil sections and higher-solidity rotors substantially reduced stall and revealed the advancing transonic flow to be a more persistent limitation to high-speed rotor performance. Work in this area was spurred not only by operational necessity but also by the development of a tool for the prediction of these flows (the method of computational fluid dynamics). The development of computational fluid dynamics for these rotor problems was a major Army and NASA achievement. This work is now being extended to other rotor flow problems. The developments are outlined.
    Schlagwort(e): AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA, Washington, NASA(Army Rotorcraft Technology. Volume 1: Aerodynamics, and Dynamics and Aeroelasticity; p 34-65
    Format: application/pdf
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  • 7
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    Some recent applications of Navier-Stokes codes to rotorcraft (1992)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: Many operational limitations of helicopters and other rotary-wing aircraft are due to nonlinear aerodynamic phenomena incuding unsteady, three-dimensional transonic and separated flow near the surfaces and highly vortical flow in the wakes of rotating blades. Modern computational fluid dynamics (CFD) technology offers new tools to study and simulate these complex flows. However, existing Euler and Navier-Stokes codes have to be modified significantly for rotorcraft applications, and the enormous computational requirements presently limit their use in routine design applications. Nevertheless, the Euler/Navier-Stokes technology is progressing in anticipation of future supercomputers that will enable meaningful calculations to be made for complete rotorcraft configurations.
    Schlagwort(e): AERODYNAMICS
    Materialart: California State Univ., The Fifth Symposium on Numerical and Physical Aspects of Aerodynamic Flows; 15 p
    Format: application/pdf
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  • 8
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    Unsteady airfoils (1982)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: Progress towards successful modelling of unsteady flows past two-dimensional oscillating airfoils is examined. Linearized, thin airfoil theory is reviewed with special regard to the vortex shedding which occurs when either the body or the flow fluctuates. A sinusoidally oscillating flat-plate airfoil is considered in terms of noncirculatory components, including boundary conditions and bound and wake vortices, respectively. Applications of linear theory to vertical airfoil oscillations and to oscillating control surfaces are described, and oscillating airfoils in subsonic and supersonic flows are investigated. Perturbations in linear solutions are explored for the occurrence of second-order effects, and trailing edge and wake effects. The effects of unsteady transonic flows are broken into nearly inviscid and strongly viscous cases, and analyses of dynamic stall and stall flutter are presented.
    Schlagwort(e): AERODYNAMICS
    Format: text
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  • 9
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    Euler solution of multiblade rotor flow (1988)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-19
    Beschreibung: A numerical method for solving the Euler equations for multiblade rotors has been developed and some preliminary results reported. The numerical scheme is a combination of several recent methods and algorithm improvements, adapted to the particular requirements of rotor-body interactions. A cylindrical basic grid has been used to study conventional multiblade helicopter rotors. Test calculations have been made for two- and six-blade rotors in hover and for a two-blade rotor in forward flight, under transonic tip conditions but without lift. The results show good agreement with experimental data.
    Schlagwort(e): AERODYNAMICS
    Materialart: Vertica (ISSN 0360-5450); 12; 3, 19; 303-313
    Format: text
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  • 10
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    Special opportunities in helicopter aerodynamics (1986)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-19
    Beschreibung: Aerodynamic research relating to modern helicopters includes the study of three dimensional, unsteady, nonlinear flow fields. A selective review is made of some of the phenomenon that hamper the development of satisfactory engineering prediction techniques, but which provides a rich source of research opportunities: flow separations, compressibility effects, complex vortical wakes, and aerodynamic interference between components. Several examples of work in progress are given, including dynamic stall alleviation, the development of computational methods for transonic flow, rotor-wake predictions, and blade-vortex interactions.
    Schlagwort(e): AERODYNAMICS
    Format: text
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