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  • 1985-1989  (29)
  • 1
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    Acoustic propagation using computational fluid dynamics (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: 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.
    Keywords: AERODYNAMICS
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  • 2
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    Airloads on bluff bodies, with application to the rotor-induced downloads on tilt-rotor aircraft (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: 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.
    Keywords: AERODYNAMICS
    Type: Vertica (ISSN 0360-5450); 9; 1, 19; 1-11
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  • 3
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    The development of CFD methods for rotor applications (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: 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.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA, Washington, NASA(Army Rotorcraft Technology. Volume 1: Aerodynamics, and Dynamics and Aeroelasticity; p 34-65
    Format: application/pdf
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  • 4
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    Euler solution of multiblade rotor flow (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: 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.
    Keywords: AERODYNAMICS
    Type: Vertica (ISSN 0360-5450); 12; 3, 19; 303-313
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  • 5
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    Special opportunities in helicopter aerodynamics (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: 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.
    Keywords: AERODYNAMICS
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  • 6
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    Calculation of helicopter airfoil characteristics for high tip-speed applications (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In this paper, we have applied a new aerodynamic tool to the study of helicopter airfoil characteristics. We have shown that the computed airloads reproduce completely the experimental behavior of representative airfoils across the transonic regime. In addition, the computational details of the flow fields, the surface pressure distributions, and the viscous-layer characteristics enable us to trace the evolution of the physical changes that occur as m infinity or Re increases. Descriptions of the complicated development of shock waves, shock-induced separation supplement the information that has been obtained heretofore in wind tunnels. In validating our calculations and assessing the accuracy of the results, including extensive grid-refinement studies and comparisons with data from numerous wind tunnels, we have defined the capabilities and limitations of the code ARC2D more precisely. This important aspect of the investigations can complement wind-tunnel tests, by providing flow-field details that are difficult to measure and by extending the range of low parameters beyond the capabilities of existing wind tunnels. The code has now progressed from a purely research stage to almost a production stage, where it can be run by specialists in the helicopter industry.
    Keywords: AERODYNAMICS
    Type: American Helicopter Society, Journal (ISSN 0002-8711); 31; 3-9
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  • 7
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    Unsteady interactions of transonic airfoils with gusts and concentrated vortices (1985)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Unsteady interactions of strong concentrated vortices, distributed gusts, and sharp-edged gusts with stationary airfoils were analyzed in two-dimensional transonic flow. A simple and efficient method for introducing such vortical disturbances was implemented in numerical codes that range from inviscid, transonic small-disturbance to thin-layer Navier Stokes. The numerical results demonstrate the large distortions in the overall flow field and in the surface air loads that are produced by various vortical interactions. The results of the different codes are in excellent qualitative agreement, but, as might be expected, the transonic small-disturbance calculations are deficient in the important region near the leading edge.
    Keywords: AERODYNAMICS
    Type: AGARD Unsteady Aerodynamics-Fundamentals and Applications to Aircraft Dynamics; 13 p
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  • 8
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    Status and prospects of computational fluid dynamics for unsteady transonic flow (1985)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Applications of computational aerodynamics to aeronautical research, design, and analysis have increased rapidly over the past decade, and these applications offer significant benefits to aeroelasticians. The past developments are traced by means of a number of specific examples, and the trends are projected over the next several years. The crucial factors that limit the present capabilities for unsteady analyses are identified; they include computer speed and memory, algorithm and solution methods, grid generation, turbulence modeling, vortex modeling, data processing, and coupling of the aerodynamic and structural dynamic analyses. The prospects for overcoming these limitations are presented, and many improvements appear to be readily attainable. If so, a complete and reliable numerical simulation of the unsteady, transonic viscous flow around a realistic fighter aircraft configuration could become possible within the next decade. The possibilities of using artificial intelligence concepts to hasten the achievement of this goal are also discussed.
    Keywords: AERODYNAMICS
    Type: AGARD Transonic Unsteady Aerodyn. and its Aeroelastic Appl.; 24 p
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  • 9
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    AGARD Fluid Dynamics Panel Symposium on Applications of Computational Fluid Dynamics in Aeronautics: Proceedings (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The Fluid Dynamics Panel of AGARD arranged a Symposium on Applications of Computational Fluid Dynamics in Aeronautics, on 7 to 10 April 1986 in Aix-en-Provence, France. The purpose of the Symposium was to provide an assessment of the status of CFD in aerodynamic design and analysis, with an emphasis on emerging applications of advanced computational techniques to complex configurations. Sessions were devoted specifically to grid generation, methods for inviscid flows, calculations of viscous-inviscid interactions, and methods for solving the Navier-Stokes equations. The 31 papers presented at the meeting are published in AGARD Conference Proceedings CP-412 and are listed in the Appendix of this report. A brief synopsis of each paper and some general conclusions and recommendations are given.
    Keywords: AERODYNAMICS
    Type: NASA-TM-88356 , A-86399 , NAS 1.15:88356 , AD-A178165
    Format: application/pdf
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  • 10
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    Tip vortices of wings in subsonic and transonic flow: A numerical simulation (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Thin layer Navier-Stokes and Euler equations are numerically solved using a multi-block zonal approach to simulate the formation and roll up of tip vortices of wings in subsonic and transonic flows. Several wing planforms were considered to examine the influence of tip-cap shape, planform geometry and free stream Mach number on the formation process. A good definition of the formation and qualitative roll up of tip vortices was achieved.
    Keywords: AERODYNAMICS
    Type: NASA-TM-88334 , A-86415 , NAS 1.15:88334 , USAAVSCOM-TM-86-A-4 , AD-A172312
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