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  • 1
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    Applications of CONMIN to wing design optimization with vortex flow effect (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Slender wings on supersonic cruise configurations are expected to be thin and highly swept. As a result, edge-separated vortex flow is inevitable and must be accounted for in aerodynamic analysis and design. The present method is based on the method of suction analogy to calculate the total aerodynamic characteristics. The method requires the solution of the attached flow problem, the latter being solved by a low-order panel method in subsonic and supersonic flow. In essence, the lifting pressure is calculated by using a pressure-doublet distribution satisfying the Prandtl-Glauert equation. From the pressure distribution, the leading-edge suction is calculated. The latter is assumed to be the vortex lift through the method of suction analogy. For a cambered wing, the location of vortex-lift action point is important in predicting the aerodynamic characteristics. It is also seen that the effect of camber shape appears nonlinearly in all aerodynamic expressions. To design the camber shape, the camber slope is represented by a cosine Fourier series at each of several spanwise stations. The Fourier coefficients are the design variables. To design a leading-edge flap in the vortex flow (i.e., a vortex flap), the coordinates of corner points and the deflection angle are the design variables. The process of wing design is to determine the camber shape and twist distribution such that an objective function, typically the drag, is minimized, subject to various constraints.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA. Langley Research Center Recent Experiences in Multidisciplinary Analysis and Optimization, Part 1; 12 p
    Format: application/pdf
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  • 2
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    Some applications of the quasi vortex-lattice method in steady and unsteady aerodynamics (1976)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The quasi vortex-lattice method is reviewed and applied to the evaluation of backwash, with applications to ground effect analysis. It is also extended to unsteady aerodynamics, with particular interest in the calculation of unsteady leading-edge suction. Some applications in ornithopter aerodynamics are given.
    Keywords: AERODYNAMICS
    Type: NASA. Langley Res. Center Vortex-Lattice Utilization; p 385-406
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  • 3
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    Wake shape and its effects on aerodynamic characteristics (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The wake shape under symmetrical flight conditions and its effects on aerodynamic characteristics are examined. In addition, the effect of wake shape in sideslip and discrete vortices such as strake or forebody vortex on lateral characteristics is presented. The present numerical method for airplane configurations, which is based on discretization of the vortex sheet into vortex segments, verified the symmetrical and asymmetrical roll-up process of the trailing vortices. Also, the effect of wing wake on tail planes is calculated. It is concluded that at high lift the assumption of flat wake for longitudinal and lateral-directional characteristics should be reexamined.
    Keywords: AERODYNAMICS
    Type: NASA-CR-178118 , NAS 1.26:178118
    Format: application/pdf
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  • 4
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    Theory of wing rock (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A theory is developed for predicting wing rock characteristics. From available data, it can be concluded that wing rock is triggered by flow asymmetries, developed by negative or weakly positive roll damping, and sustained by nonlinear aerodynamic roll damping. A new nonlinear aerodynamic model that includes all essential aerodynamic nonlinearities is developed. The Beecham-Titchener method is applied to obtain approximate analytic solutions for the amplitude and frequency of the limit cycle based on the three degree-of-freedom equations of motion. An iterative scheme is developed to calculate the average aerodynamic derivatives and dynamic characteristics at limit cycle conditions. Good agreement between theoretical and experimental results is obtained.
    Keywords: AERODYNAMICS
    Type: NASA-CR-176640 , NAS 1.26:176640 , CRINC-FRL-516-1
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  • 5
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    Calculation of asymmetric vortex separation on slender delta wings with a vortex-sheet model (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An inviscid vortex-sheet model based on the slender wing theory is developed to examine asymmetric vortex separation at zero sideslip on delta wings. It is found that multiple asymmetric vortex configurations exist at a given angle of attack. Available data on rolling moment measurements and flow visualization are used for correlation to prove the concept.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 86-1836
    Format: text
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  • 6
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    Investigation of empennage buffeting (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Theoretical methods of predicting aircraft buffeting are reviewed. For the buffeting due to leading edge vortex breakdown, a method is developed to convert test data of mean square values of fluctuating normal force to buffeting vortex strength through an unsteady lifting-surface theory and unsteady suction analogy. The resulting buffeting vortex from the leading edge extension of an F-18 configuration is used to generate a fluctuating flow field which produces unsteady pressure distribution on the vertical tails. The root mean square values of root bending moment on the vertical tails are calculated for a rigid configuration.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA-CR-177164 , NAS 1.26:177164 , CRINC-FRL-714-1
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  • 7
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    Extensions of the concept of suction analogy to prediction of vortex lift effect (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Flow field data for a double delta wing at low speed were used to determine the location of a vortex action point. The result was found to be consistent with what was determined for a delta wing. In supersonic flow, the action point location was determined empirically. For a wing with rounded leading edges, an assumption for initial vortex separation was shown to be equivalent to initial leading edge bubble separation for airfoils. A theoretical formulation by the section analogy to determine the delayed vortex separation on a cambered wing with rounded leading edges was presented. The method of suction analogy was further shown to be applicable to predicting the body vortex lift.
    Keywords: AERODYNAMICS
    Type: NASA. Langley Research Center Vortex Flow Aerodynamics, Vol. 1; p 65-84
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  • 8
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    Transonic airfoil analysis and design in nonuniform flow (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A nonuniform transonic airfoil code is developed for applications in analysis, inverse design and direct optimization involving an airfoil immersed in propfan slipstream. Problems concerning the numerical stability, convergence, divergence and solution oscillations are discussed. The code is validated by comparing with some known results in incompressible flow. A parametric investigation indicates that the airfoil lift-drag ratio can be increased by decreasing the thickness ratio. A better performance can be achieved if the airfoil is located below the slipstream center. Airfoil characteristics designed by the inverse method and a direct optimization are compared. The airfoil designed with the method of direct optimization exhibits better characteristics and achieves a gain of 22 percent in lift-drag ratio with a reduction of 4 percent in thickness.
    Keywords: AERODYNAMICS
    Type: NASA-CR-3991 , NAS 1.26:3991 , CRINC-FRL-602-2
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  • 9
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    Unsteady aerodynamic models for maneuvering aircraft (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Forced oscillation tests over a large angle-of-attack range for an F-18 model are conducted in the NASA Langley 12-foot low-speed tunnel. The resulting dynamic longitudinal data are analyzed with an unsteady aerodynamic modeling method based on Fourier functional analysis and the indicial formulation. The method is extensively examined and improved to automate the calculation of model coefficients, and to evaluate more accurately the indicial integral. The results indicate that the general model equation obtained from harmonic test data in a range of reduced frequency is capable of accurately modeling the nonlinear responses with large hysteresis effect, except in the region where a delayed flow reattachment occurs at low angles of attack in down strokes. The indicial formulation is used to calculate the response to harmonic motion, harmonic ramp motion, constant-rate pitching motion and smaller-amplitude harmonic motion. The results show that more accurate results can be obtained when the motion starts from a low angle of attack where hysteresis effect is not important.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: AIAA PAPER 93-3626 , In: AIAA Atmospheric Flight Mechanics Conference, Monterey, CA, Aug. 9-11, 1993, Technical Papers (A93-48301 20-08); p. 97-112.
    Format: text
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  • 10
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    VORCOR: A computer program for calculating characteristics of wings with edge vortex separation by using a vortex-filament and-core model (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A computer code base on an improved vortex filament/vortex core method for predicting aerodynamic characteristics of slender wings with edge vortex separations is developed. The code is applicable to camber wings, straked wings or wings with leading edge vortex flaps at subsonic speeds. The prediction of lifting pressure distribution and the computer time are improved by using a pair of concentrated vortex cores above the wing surface. The main features of this computer program are: (1) arbitrary camber shape may be defined and an option for exactly defining leading edge flap geometry is also provided; (2) the side edge vortex system is incorporated.
    Keywords: AERODYNAMICS
    Type: NASA-CR-165902 , NAS 1.26:165902
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