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  • AERODYNAMICS  (56)
  • 1
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    Numerical solutions of forward-flight rotor flow using an upwind method (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 374-380
    Format: text
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  • 2
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    Acoustic propagation using computational fluid dynamics (1986)
    In:  Other Sources
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    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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  • 3
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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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  • 4
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    Some recent applications of Navier-Stokes codes to rotorcraft (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: 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.
    Keywords: AERODYNAMICS
    Type: California State Univ., The Fifth Symposium on Numerical and Physical Aspects of Aerodynamic Flows; 15 p
    Format: application/pdf
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  • 5
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    Unsteady airfoils (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: 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.
    Keywords: AERODYNAMICS
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  • 6
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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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  • 7
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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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  • 8
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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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  • 9
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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
    Format: text
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  • 10
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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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