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  • AERODYNAMICS  (569)
  • ddc:330
  • 1985-1989  (569)
  • 1950-1954
  • 1985  (569)
  • 1
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    Steady and unsteady incompressible free-wake analysis (1985)
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    Publication Date: 2011-08-19
    Description: The flows around highly sweptback wings and bodies of revolution at high angle of attack are described, and inviscid model approximations and mathematical formulation of the problem are given to steady and unsteady incompressible flows. A general presentation of the methods of solution is given, with emphasis on current computational techniques. Detailed descriptions of the nonlinear vortex-lattice and vortex-panel techniques are presented to show how the boundary conditions are enforced using iteration. Typical numerical results are compared with the available experimental data.
    Keywords: AERODYNAMICS
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  • 2
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    Finite difference methods for the solution of unsteady potential flows (1985)
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    Publication Date: 2011-08-19
    Description: A brief review is presented of various problems which are confronted in the development of an unsteady finite difference potential code. This review is conducted mainly in the context of what is done for a typical small disturbance and full potential methods. The issues discussed include choice of equation, linearization and conservation, differencing schemes, and algorithm development. A number of applications including unsteady three-dimensional rotor calculation, are demonstrated.
    Keywords: AERODYNAMICS
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  • 3
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    Unsteady transonic flows - Introduction, current trends, applications (1985)
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    Publication Date: 2011-08-19
    Description: The computational treatment of unsteady transonic flows is discussed, reviewing the historical development and current techniques. The fundamental physical principles are outlined; the governing equations are introduced; three-dimensional linearized and two-dimensional linear-perturbation theories in frequency domain are described in detail; and consideration is given to frequency-domain FEMs and time-domain finite-difference and integral-equation methods. Extensive graphs and diagrams are included.
    Keywords: AERODYNAMICS
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  • 4
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    Unsteady subsonic and supersonic flows - Historical review; state of the art (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This lecture is introductory to the subject of unsteady subsonic and supersonic flows. The primary objective is to present fundamental concepts in order to promote an understanding of the relations between the basic physical problems and their mathematical formulation as well as to establish a common foundation for the more detailed presentations of subsequent lectures in this session. Linearized (small-perturbation) potential flow is emphasized, although needs beyond that limit are indicated. The basic equations, concepts, and procedures common to all the methods are reviewed first, followed by the development, discussion, and status of methods for creating two-dimensional incompressible flow, strip theory, subsonic lifting-surface theory, subsonic/supersonic surface-panel methods, and supersonic lifting-surface theory.
    Keywords: AERODYNAMICS
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  • 5
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    Overview of helicopter wake and airloads technology (1985)
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    Publication Date: 2011-08-19
    Description: An overview of helicopter aerodynamics technology is presented with emphasis on rotor wake and airloads methodology developed at the United Technologies Research Center (UTRC). The evolution over the past twenty years of various levels of computerized wake geometry models at UTRC, such as undistorted wake, prescribed empirical wake, predicted distorted wake, and generalized wake models for the hover and forward flight regimes, is reviewed. The requirement for accurate wake modeling for flow field and airload prediction is demonstrated by comparisons of theoretical and experimental results. These results include blade pressure distributions predicted from a recently developed procedure for including the rotor wake influence in a full potential flow analysis. Predictions of the interactional aerodynamics of various helicopter components (rotor, fuselage, and tail) are also presented. It is concluded that, with advanced computers and the rapidly progressing computational aerodynamics technology, significant progress toward reliable prediction of helicopter airloads is forseeable in the near future.
    Keywords: AERODYNAMICS
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  • 6
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    Application of optical interferometry in compressible flows (1985)
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    Publication Date: 2011-08-19
    Description: Interferometry methods were applied to the investigation of steady and unsteady flows in large scale transonic wind tunnels. Holographic interferometry was demonstrated to provide reliable flow visualization and quantitative results for a number of two-dimensional flows. These conclusions were based on extensive comparisons with results obtained by other means. Data obtained on a NACA 64A010 airfoil with an oscillating flap installed in the Ames 11-foot transonic tunnel are presented. Interferograms were recorded at a free stream Mach number of 0.8, flap frequency of 30 Hertz and chord Reynolds numbers of 6.6 x 10 to the 6th and 12.3 x 10 to the 6th. The interferometric results were reduced to dynamic surface pressures, Mach contours and wake flow profiles. A new interferometry method that is capable of providing real-time interferometry data is also discussed.
    Keywords: AERODYNAMICS
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  • 7
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    The aerodynamics of rotor blades with ice shapes accreted in hover and in level flight (1985)
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    Publication Date: 2011-08-19
    Description: Through a series of flights in artificial clouds, ice accretions on the main rotor of a UH-1H helicopter were documented in detail upon landing by silicone-rubber molds for both hover and level flights. Full scale reproductions of typical accretions in hover were fabricated by means of epoxy castings and used for a wind-tunnel test program. Surface static pressure distributions were recorded and used to evaluate lift and pitching moment increments while drag was determined by wake surveys. For comparison, accreted ice shapes are presented for two level flight cases as well as preliminary analytical predictions.
    Keywords: AERODYNAMICS
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  • 8
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    Three-dimensional inviscid analysis of radial-turbine flow and a limited comparison with experimental data (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The three-dimensional inviscid DENTON code is used to analyze flow through a radial-inflow turbine rotor. Experimental data from the rotor are compared with analytical results obtained by using the code. The experimental data available for comparison are the radial distributions of circumferentially averaged values of absolute flow angle and total pressure downstream of the rotor exit. The computed rotor-exit flow angles are generally underturned relative to the experimental values, which reflect the boundary-layer separation at the trailing edge and the development of wakes downstream of the rotor. The experimental rotor is designed for a higher-than-optimum work factor of 1.126 resulting in a nonoptimum positive incidence and causing a region of rapid flow adjustment and large velocity gradients. For this experimental rotor, the computed radial distribution of rotor-exit to turbine-inlet total pressure ratios are underpredicted due to the errors in the finite-difference approximations in the regions of rapid flow adjustment, and due to using the relatively coarser grids in the middle of the blade region where the flow passage is highly three-dimensional. Additional results obtained from the three-dimensional inviscid computation are also presented, but without comparison due to the lack of experimental data. These include quasi-secondary velocity vectors on cross-channel surfaces, velocity components on the meridional and blade-to-blade surfaces, and blade surface loading diagrams. Computed results show the evolution of a passage vortex and large streamline deviations from the computational streamwise grid lines. Experience gained from applying the code to a radial turbine geometry is also discussed.
    Keywords: AERODYNAMICS
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  • 9
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    Finite-difference computations of rotor loads (1985)
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    Publication Date: 2011-08-19
    Description: This paper demonstrates the current and future potential of finite-difference methods for solving real rotor problems which now rely largely on empiricism. The demonstration consists of a simple means of combining existing finite-difference, integral, and comprehensive loads codes to predict real transonic rotor flows. These computations are performed for hover and high-advance-ratio flight. Comparisons are made with experimental pressure data.
    Keywords: AERODYNAMICS
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  • 10
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    Scale-model tests of airfoils in simulated heavy rain (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 536-540
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  • 11
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    An investigation of the tabbed vortex flap (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 490-497
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  • 12
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    Assessment of preliminary prediction techniques for wing leading-edge vortex flows at supersonic speeds (1985)
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    Publication Date: 2011-08-19
    Description: A theoretical investigation of the aerodynamics of sharp leading-edge delta wings at supersonic speeds has been conducted. The primary objective of this was to determine the applicability of existing theoretical methods to predict wing leading-edge separated-flow characteristics at conditions conductive to high-lift supersonic flight. Predicted results from two modified linear-theory methods (LTSTAR and VORCAM) are compared with experimental data. Comparison of the two methods for uncambered wings revealed that the LTSTAR code is in much better agreement with experimentally measured vortex strength, vortex position, and total lifting characteristics than the VORCAM code. Selected analysis was also performed with an Euler code, SWINT. The results of this study indicated that the SWINT code was not well suited to the analysis of wings with separated flow at high lift and low supersonic speeds.
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 473-478
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  • 13
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    Comparison of inviscid flow computations with flight data for the Shuttle orbiter (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 22; 297-303
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  • 14
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    The lateral surface drag coefficient of cylindrical spacecraft in a rarefied finite temperature atmosphere (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In the present determination of the free molecule flow drag coefficient for a cylindrical spacecraft flying parallel to its principal axis, the lateral surface effects of thermal motion are explicitly included in terms of the average impact angle of the incident gas momentum vector. Kinetic theory is used to characterize self-shadowing, as well as to obtain an expression for the lateral surface coefficient in terms of the average impact angle of the incident momentum vector and the fractional momentum transfer along the line of impact. It is found that, for a length/diameter ratio of about 5, the lateral surface contribution to the drag coefficient is comparable to that of the front face.
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 862-867
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  • 15
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    Axisymmetric bluff-body drag reduction through geometrical modification (1985)
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    Publication Date: 2011-08-19
    Description: The effect of shoulder radiusing and grooving (longitudinally and circumferentially) the afterbodies of bluff bodies to reduce the base drag at low speeds is investigated experimentally. Shoulder radii as large as 2.75 body diameters are examined. Reynolds number (ReD) based on body diameter varied from 20,000 to 200,000. Results indicate that increasing the shoulder radius to 2.00 body diameters can reduce the drag levels to those of a streamline body having 67 percent greater fineness ratio. For the relatively sharp shoulder case, body drag reductions as large as 50 and 33 percent are obtained using circumferential or longitudinal grooves, respectively.
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 516-522
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  • 16
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    Measured and calculated airloads on a transport wing model (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 336-342
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  • 17
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    Euler and Navier-Stokes solutions for supersonic shear flow past a circular cylinder (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 583-587
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  • 18
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    Implicit Total Variation Diminishing (TVD) schemes for steady-state calculations (1985)
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    Publication Date: 2011-08-19
    Description: The novel implicit and unconditionally stable, high resolution Total Variation Diminishing (TVD) scheme whose application to steady state calculations is presently examined is a member of a one-parameter family of implicit, second-order accurate systems developed by Harten (1983) for the computation of weak solutions for one-dimensional hyperbolic conservation laws. The scheme will not generate spurious oscillations for a nonlinear scalar equation and a constant coefficient system. Numerical experiments for a quasi-one-dimensional nozzle problem show that the experimentally determined stability limit correlates exactly with the theoretical stability limit for the nonlinear scalar hyberbolic conservation laws.
    Keywords: AERODYNAMICS
    Type: Journal of Computational Physics (ISSN 0021-9991); 57; 327-360
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  • 19
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    Evaluation of a stalled airfoil analysis program (1985)
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    Publication Date: 2011-08-19
    Description: The Stalled Airfoil Analysis Program (SAAP) is a computer code for predicting the aerodynamic characteristics of an airfoil up to, and beyond, stall. SAAP is presently evaluated through comparisons with experiments and with two other theoretical methods over an extensive range of airfoils and Reynolds number conditions. SAAP modeled drag more accurately than either of the other methods, and at angles of attack below stall yielded a smoother lift variation with angle of attack.
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 156
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  • 20
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    A wind tunnel inlet flow simulation (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 927
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  • 21
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    Full potential solutions of three-dimensional supersonic flows (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 881-887
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  • 22
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    Numerical optimization of circulation control airfoil at high subsonic speed (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 869-874
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  • 23
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    Inviscid and viscous flows in cascades with an explicit multiple-grid algorithm (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 1556-156
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  • 24
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    A computational study of complex three-dimensional compressible turbulent flowfields (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 1461
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  • 25
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    Flow instabilities in transonic small-disturbance theory (1985)
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    Publication Date: 2011-08-19
    Description: The dynamics of unsteady transonic small disturbance flows about two-dimensional airfoils is examined, with emphasis on the behavior in the region where the steady state flow is nonunique. It is shown that nonuniqueness results from an extremely long time scale instability which occurs in a finite Mach number and angle of attack range. The similarity scaling rules for the instability are presented and the possibility of similar behvior in the Euler equations is discussed.
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 1491-149
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  • 26
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    Effects of viscosity and modes on transonic aerodynamic and aeroelastic characteristics of wings (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 756-762
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  • 27
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    Convergence characteristics of a vortex-lattice method for nonlinear configuration aerodynamics (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 743-749
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  • 28
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    Navier-Stokes computations of projectile base flow with and without mass injection (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 1348-135
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  • 29
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    Comparison of supercritical airfoil flow calculations with wind tunnel results (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 1301-130
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  • 30
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    Fundamental aerodynamic characteristics of delta wings with leading-edge vortex flows (1985)
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    Publication Date: 2011-08-19
    Description: An investigation of the aerodynamics of sharp leading-edge delta wings at supersonic speeds has been conducted. The supporting experimental data for this investigation were taken from published force, pressure, and flow-visualization data in which the Mach number normal to the wing leading edge is always less than 1.0. The individual upper- and lower-surface nonlinear characteristics for uncambered delta wings are determined and presented in three charts. The upper-surface data show that both the normal-force coefficient and minimum pressure coefficient increase nonlinearly with a decreasing slope with increasing angle of attack. The lower-surface normal-force coefficient was shown to be independent of Mach number and to increase nonlinearly, with an increasing slope, with increasing angle of attack. These charts are then used to define a wing-design space for sharp leading-edge delta wings.
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 479-485
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  • 31
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    Extension of equivalent angle-of-attack method for nonlinear flowfields (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 22; 304-308
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  • 32
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    Rotor/body aerodynamic interactions (1985)
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    Publication Date: 2011-08-19
    Description: A wind tunnel investigation was conducted in which independent, steady state aerodynamic forces and moments were measured on a 2.24 m diam. two bladed helicopter rotor and on several different bodies. The mutual interaction effects for variations in velocity, thrust, tip-path-plane angle of attack, body angle of attack, rotor/body position, and body geometry were determined. The results show that the body longitudinal aerodynamic characteristics are significantly affected by the presence of a rotor and hub, and that the hub interference may be a major part of such interaction. The effects of the body on the rotor performance are presented.
    Keywords: AERODYNAMICS
    Type: Vertica (ISSN 0360-5450); 9; 1, 19; 65-81
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  • 33
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    Airloads on bluff bodies, with application to the rotor-induced downloads on tilt-rotor aircraft (1985)
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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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  • 34
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    Viscous shock-layer flowfield analysis by an explicit-implicit method (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 723-732
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  • 35
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    Analysis of aerothermal loads on spherical dome protuberances (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 650-656
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  • 36
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    Impact of fuselage incidence on the supersonic aerodynamics of two fighter configurations (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 423-428
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  • 37
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    Aerodynamics of generalized bent biconics for aero-assisted, orbital-transfer vehicles (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 22; 104-111
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  • 38
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    Efficient algorithm for unsteady transonic aerodynamics of low-aspect-ratio wings (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 193-199
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  • 39
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    Implicit upwind methods for the compressible Navier-Stokes equations (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 374-380
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  • 40
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    Shock-free turbomachinery blade design (1985)
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    Publication Date: 2011-08-19
    Description: A computational method for designing shock-free, quasi-three-dimensional, transonic, turbomachinery blades is described. Shock-free designs are found by implementing Sobieczky's fictitious gas principle in the analysis of a baseline shape, resulting in an elliptic solution that is incorrect in the supersonic domain. Shock-free designs are obtained by combining the subsonic portion of this solution with a characteristic calculation of the correct supersonic flow using the sonic line data from the fictitious elliptic solution. This provides a new, shock-free blade design. Examples presented include the removal of shocks from two blades in quasi-three-dimensional flow and the development of a series of shock-free two-dimensional stators. The new designs all include modifications to the upper surface of an experimental stator blade developed at NASA Lewis Research Center. While the designs presented here are for inviscid flow, the same concepts have been successfully applied to the shock-free design of airfoils and three-dimensional wings with viscous effects. The extension of the present method to viscous flows is straightforward given a suitable analysis algorithm for the flow.
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 249-253
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  • 41
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    Chemical nonequilibrium effects on flowfields for aeroassisted orbital transfer vehicles (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 22; 54-59
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  • 42
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    Introductory aerothermodynamics of advanced space transportation systems (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 22; 19-26
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  • 43
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    Efficient solution of the Euler and Navier-Stokes equations with a vectorized multiple-grid algorithm (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 23-32
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  • 44
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    Dynamic response characteristics of a circulation control rotor model pneumatic system (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Numerical and experimental simulation of unsteady airflow through the control valve and slotted air duct of a circulation control rotor is described. The numerical analysis involves the solution of the quasi-one-dimensional compressible fluid-dynamic equations in the blade air duct together with the coupled isentropic flow equations for flow into the blade through the valve and out of the blade through the Coanda slot. Numerical solutions are compared with basic experimental results obtained for a mockup of a circulation control rotor and its pneumatic valving system. The pneumodynamic phenomena that were observed are discussed with particular emphasis on the characteristic system time lags associated with the response of the flow variables to transient and periodic control valve inputs.
    Keywords: AERODYNAMICS
    Type: NASA. Ames Research Center Rotorcraft Dynamics 1984; p 273-285
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  • 45
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    A review of dynamic inflow and its effect on experimental correlations (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A review is given of the relationship between experimental data and the development of modern dynamic-inflow theory. Some of the most interesting data, first presented 10 years ago at the Dynamic Specialist's Meeting, is now reviewed in light of the newer theories. These pure blade-flapping data correlate very well with analyses that include the new dynamic inflow theory, thus verifying the theory. Experimental data are also presented for damping with coupled inplane and body motions. Although inclusion of dynamic inflow is often required to correlate this coupled data, the data cannot be used to verify any particular dynamic inflow theory due to the uncertainties in modeling the inplane degree of freedom. For verification, pure flapping is required. However, the coupled data do show that inflow is often important in such computations.
    Keywords: AERODYNAMICS
    Type: NASA. Ames Research Center Rotorcraft Dynamics 1984; p 187-205
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  • 46
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    Aeroelastic considerations for torsionally soft rotors (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A research study was initiated to systematically determine the impact of selected blade tip geometric parameters on conformable rotor performance and loads characteristics. The model articulated rotors included baseline and torsionally soft blades with interchangeable tips. Seven blade tip designs were evaluated on the baseline rotor and six tip designs were tested on the torsionally soft blades. The designs incorporated a systemmatic variation in geometric parameters including sweep, taper, and anhedral. The rotors were evaluated in the NASA Langley Transonic Dynamics Tunnel at several advance ratios, lift and propulsive force values, and tip Mach numbers. A track sensitivity study was also conducted at several advance ratios for both rotors. Based on the test results, tip parameter variations generated significant rotor performance and loads differences for both baseline and torsionally soft blades.
    Keywords: AERODYNAMICS
    Type: NASA. Ames Research Center Rotorcraft Dynamics 1984; p 117-136
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  • 47
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    Development of an unsteady aerodynamics model to improve correlation of computed blade stresses with test data (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A reliable rotor aeroelastic analysis operational that correctly predicts the vibration levels for a helicopter is utilized to test various unsteady aerodynamics models with the objective of improving the correlation between test and theory. This analysis called Rotor Aeroelastic Vibration (RAVIB) computer program is based on a frequency domain forced response analysis which utilizes the transfer matrix techniques to model helicopter/rotor dynamic systems of varying degrees of complexity. The results for the AH-1G helicopter rotor were compared with the flight test data during high speed operation and they indicated a reasonably good correlation for the beamwise and chordwise blade bending moments, but for torsional moments the correlation was poor. As a result, a new aerodynamics model based on unstalled synthesized data derived from the large amplitude oscillating airfoil experiments was developed and tested.
    Keywords: AERODYNAMICS
    Type: NASA. Ames Research Center Rotorcraft Dynamics 11984; p 103-116
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  • 48
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    Lifting surface theory for a helicopter rotor in forward flight (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A lifting surface theory was developed for a helicopter rotor in forward flight for compressible and incompressible flow. The method utilizes the concept of the linearized acceleration potential and makes use of the vortex lattice procedure. Calculations demonstrating the application of the method are given in terms of the lift distribution on a single rotor, a two-bladed rotor, and a rotor with swept-forward and swept-back tips. In addition, the lift on a rotor which is vibrating in a pitching mode at 4/rev is given. Compressibility effects and interference effects for a two-bladed rotor are discussed.
    Keywords: AERODYNAMICS
    Type: NASA. Ames Research Center Rotorcraft Dynamics 1984; p 89-101
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  • 49
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    Orbiter entry aerothermodynamics (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The challenge in the definition of the entry aerothermodynamic environment arising from the challenge of a reliable and reusable Orbiter is reviewed in light of the existing technology. Select problems pertinent to the orbiter development are discussed with reference to comprehensive treatments. These problems include boundary layer transition, leeward-side heating, shock/shock interaction scaling, tile gap heating, and nonequilibrium effects such as surface catalysis. Sample measurements obtained from test flights of the Orbiter are presented with comparison to preflight expectations. Numerical and wind tunnel simulations gave efficient information for defining the entry environment and an adequate level of preflight confidence. The high quality flight data provide an opportunity to refine the operational capability of the orbiter and serve as a benchmark both for the development of aerothermodynamic technology and for use in meeting future entry heating challenges.
    Keywords: AERODYNAMICS
    Type: Space Shuttle Tech. Conf., Pt. 2; p 1051-1061
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  • 50
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    Accelerated solution of the steady Euler equations (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The present paper is concerned with two methods for the accelerated solution of the steady Euler equations. One method makes use of a second-order embedding to facilitate the derivation of the relaxation solution of the steady equations of motion, while the other method employs a multile-gridding concept to accelerate the convergence of a simple, explicit, time-marching scheme applied to the unsteady equations. It is pointed out that the surrogate equation technique provides a means for formulating problems involving the full steady Euler equations in such a way as to allow the use of relaxation solution procedures. It is, therefore, possible to solve either irrotational or rotational flow problems spanning the entire spectrum of subsonic, transonic, and supersonic conditions. The solutions can be obtained without an employement of either derived dependent variables, semidirect methods, or an unsteady formulation.
    Keywords: AERODYNAMICS
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  • 51
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    Numerical algorithms for transonic inviscid flow calculations (1985)
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    Publication Date: 2011-08-19
    Description: It is pointed out that the supercritical wing is one of the most important features of modern transonic aerodynamics. The design of its shock free airfoil section depends on potential flow calculations. The present paper is concerned with the development of inviscid flow simulation methods based on potential formulations, taking into account also the problem of nonuniqueness of the potential solution. Nonisentropic and nonisoenergetic models are considered, and an alternative approach using the stream function is discussed. Attention is given to transonic small disturbance calculations, calculations based on the full potential equation, iterative methods, wave drag calculations, and an alternative form of Euler equations.
    Keywords: AERODYNAMICS
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  • 52
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    A theoretical basis for extending surface-paneling methods to transonic flow (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The surface integral terms in Green's third identity are often used to solve the Prandtl-Glauert (linear potential-flow) equation with panel methods. This can be done, as in the PAN AIR code, for either subsonic or supersonic flow about complete aircraft. The extension to transonic flow is suggested by the volume integral terms of Green's third identity. The mathematical basis for this extension, without the use of body-fitted grids, is presented. Supercritical transonic results computed from a two-dimensional transonic PAN AIR research code demonstrate the method.
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 1860-186
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  • 53
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    Finite difference solutions of the Euler equations in the vicinity of sharp edges (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Attempts have been made to explain why finite difference solutions of the Euler equations can describe flows with large vortical structures around sharp-edged bodies. The present paper is concerned with the influence of a singular sharp edge on the truncation error for a set of discretized Euler equations. An analysis is conducted of the distribution of the truncation error of one finite difference approximation of the Euler equations near a sharp edge of a thin plate. The analysis leads to a determination of the size of the region of the neighborhood of such a singularity. Attention is given to the consistency of a discretization of the Euler equations, and numerical experiments.
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 1820-182
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  • 54
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    Second-order-accurate spatial differencing for the transonic small-disturbance equation (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 1693-169
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  • 55
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    Numerical simulation of self-excited oscillations in a ramjet inlet-diffuser flow (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper describes numerical simulations of self-excited oscillations in a two-dimensional transonic inlet-diffuser flow by solving the Navier-Stokes equations with a two-equation turbulence model. The calculated amplitudes of oscillations for the terminal shock and the velocity fields compare well with experimental measurements; however, the predicted frequency of oscillations is about 50 percent higher. The formation of a pair of downstream-traveling, counter-rotating vortices at each cycle of velocity fluctuations, as reported experimentally, is vividly revealed by the numerical results.
    Keywords: AERODYNAMICS
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  • 56
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    Implicit finite-difference methods for the Euler equations (1985)
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    Publication Date: 2011-08-19
    Description: The present paper is concerned with two-dimensional Euler equations and with schemes which are in use of the time of this writing. Most of the development presented carries over directly to three dimensions. The characteristics of the two-dimensional Euler equations in Cartesian coordinates are considered along with generalized curvilinear coordinate transformations, metric relations, invariants of the transformation, flux Jacobian matrices and eigensystems, numerical algorithms, flux split algorithms, implicit and explicit nonlinear control (smoothing), upwind differencing in supersonic regions, unsteady and steady-state computation, the diagonal form of implicit algorithm, metric differencing and invariants, boundary conditions, geometry and mesh generation, and sample solutions.
    Keywords: AERODYNAMICS
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  • 57
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    Foundations for the numerical solution of the Euler equations (1985)
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    Publication Date: 2011-08-19
    Description: The Navier-Stokes equations represent an extremely good model of the physical phenomena encountered in most aeronautical problems. However, the computational resource needed to solve the Navier-Stokes equations are so large that even with today's supercomputers, it is necessary to make use of simpler models. A large number of external aerodynamic problems can be accurately described by a simpler model. This model consists of an outer inviscid flow plus a boundary-layer thickness correction for the vehicle shape. The outer inviscid model may be represented by the potential equation or by the Euler equation. The present paper provides the foundations for the numerical solution of the Euler equations. The governing equations are considered, taking into account conservation laws, the medium, the differential form of the conservation laws, generalized solutions, shock-fitting, and characteristics. Attention is also given to initial and boundary conditions, existence and uniqueness, and rotational phenomena.
    Keywords: AERODYNAMICS
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  • 58
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    A comparative study of the parabolized Navier-Stokes code using various grid-generation techniques (1985)
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    Publication Date: 2011-08-19
    Description: The parabolized Navier-Stokes (PNS) equations are used to calculate the flow-field characteristics about the hypersonic research aircraft X-24C. A comparison of the results obtained using elliptic, hyperbolic and algebraic grid generators is presented. The outer bow shock is treated as a sharp discontinuity, and the discontinuities within the shock layer are captured. Surface pressures and heat-transfer results at angles of attack of 6 deg and 20 deg, obtained using the three grid generators, are compared. The PNS equations are marched downstream over the body in both Cartesian and cylindrical base coordinate systems, and the results are compared. A robust marching procedure is demonstrated by successfully using large marching-step sizes with the implicit shock fitting procedure. A correlation is found between the marching-step size, Reynolds number and the angle of attack at fixed values of smoothing and stability coefficients for the marching scheme.
    Keywords: AERODYNAMICS
    Type: Computers and Fluids (ISSN 0045-7930); 13; 4, 19
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  • 59
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    Vortex generators as a means for increasing rotor performance (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Field tests on a horizontal axis wind turbine (HAWT) have shown that Vortex Generators (VGs) can increase the efficiency of large propeller type (horizontal axis) wind turbines. VGs are devices which are attached to the surfaces of an aerodynamic body to influence the boundary layer behavior. It is pointed out that VGs were originally developed for delaying stall on aircraft wings. An investigation was conducted regarding the possibility to employ VGs also for the improvement of the performance of an intermediate size HAWT with a diameter in the range from 24 to 46 meters. This investigation included wind tunnel tests involving a rotor blade tip section, and field tests. The wind tunnel tests showed that VGs can improve the peak lift capabilities of the section while only slightly increasing the drag. The field tests showed that VGs can increase the rotor power in winds above 6 m/s.
    Keywords: AERODYNAMICS
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  • 60
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    Computations of unsteady transonic flows (1985)
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    Publication Date: 2011-08-19
    Description: During the last eight years, the subject of computational unsteady transonic aerodynamics has undergone a period of rapid growth. A brief survey of some of the fundamental advances during this period is provided, and some of the research done at NASA Ames Research Center is described in detail. The small-distance potential equation is considered, taking into account features of the unsteady transonic flow, the governing equation, the pressure coefficient, the wake condition, the airfoil tangency condition, the downstream boundary condition, the alternating direction implicit (ADI) algorithm, a grid system, boundary conditions, an airfoil with oscillating trailing edge flap, three types of shock-wave motion, and an example of a simple aeroelastic problem. A description is given of an implicit algorithm for the unsteady full potential equation in conservation form.
    Keywords: AERODYNAMICS
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  • 61
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    Approximate-factorization schemes for solving the transonic full-potential equation (1985)
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    Publication Date: 2011-08-19
    Description: The present paper provides a general discussion of approximate-factorization techniques applied to the transonic full-potential equation. Giving particular attention to the AF2 approximate-factorization scheme. This scheme was first introduced by Ballhaus and Steger (1975) for solving the low-frequency (unsteady), transonic small-disturbance equation. The full-potential equation algorithm is examined, taking into account the governing equations, grid generation, the artificial density scheme (spatial differencing), the alternating direction implicit scheme, the AF2 iteration scheme, temporal damping, and boundary conditions. Computed results are also presented. It is shown that fast, fully-implicit algorithms of the approximate-factorization variety are both efficient and reliable for solving the conservative full-potential equation.
    Keywords: AERODYNAMICS
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  • 62
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    Separation bubble behavior for a NACA 23009 airfoil (1985)
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    Publication Date: 2011-08-19
    Description: Results are reported of experiments with smoke-wire flow visualization applied to characterizing the conditions conducive to formation of a separation bubble on an airfoil in low Re flow. An airfoil was used which spanned the test channel of the wind tunnel designed for low turbulence and noise. A wire coated with mineral oil was stretched across the channel upstream of the airfoil and heated. The smoke it gave off was flash-illuminated and photographed with ASA 3000 film. Extending the airfoil over the entire section yielded photographs that gave an essentially two-dimensional perspective. Angles of attack from 0-10 deg were investigated at Re of 33,000, 66,000, 100,000 and 133,000. Sample photographs illustrate the usefulness of the technique and apparatus in the flow regimes examined, particularly when used in conjunction with pressure tap data from the airfoil surface.
    Keywords: AERODYNAMICS
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    Airfoil design for Reynolds numbers between 50,000 and 500,000 (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The design of airfoils for flows with Re of 50,000-500,000 requires consideration of laminar separation bubbles. A design approach is discussed which specifies the angle of attack at which the potential flow velocity is to be constant at each segment of the airfoil. The velocity gradient is controlled by introducing a pressure recovery function at the trailing edge. Boundary layer stability decreases with rising Re, although an upper Re value can be identified, below which the boundary layer will be stable. Adverse pressure gradients are associated with the shape parameter of the velocity profile, whose rise in value decreases stability. Transition displays similar relationships to the shape parameter. The most frequent feature of separation is the appearance of a separation bubble.
    Keywords: AERODYNAMICS
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  • 64
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    High angle-of-attack calculations of the subsonic vortex flow on slender bodies (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 1150-115
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  • 65
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    Natural laminar flow hits smoother air (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Natural laminar flow (NLF) may be attained in aircraft with lower cost, weight, and maintenance penalties than active flow laminarization by means of a slot suction system. A high performance general aviation jet aircraft possessing a moderate degree of NLF over wing, fuselage, empennage and engine nacelles will accrue a 24 percent reduction in total aircraft drag in the cruise regime. NASA-Langley has conducted NLF research centered on the use of novel airfoil profiles as well as composite and milled aluminum alloy construction methods which minimize three-dimensional aerodynamic surface roughness and waviness. It is noted that higher flight altitudes intrinsically reduce unit Reynolds numbers, thereby minimizing turbulence for a given cruise speed.
    Keywords: AERODYNAMICS
    Type: Aerospace America (ISSN 0740-722X); 23; 60
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  • 66
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    Computer studies of hybrid slotted working sections with minimum steady interference at subsonic speeds (1985)
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    Publication Date: 2011-08-19
    Description: Currently there is renewed interest in the evaluation and reduction of steady wind tunnel wall interference, especially for large models. Evaluation of previous predictions for perforated and slotted tunnels suggests that a hybrid slotted tunnel (i.e., a slotted tunnel with closed slats and perforated slots) should offer minimum corrections for upwash, flow curvature and solid blockage. This suggestion is confirmed by the present computer studies of a range of rectangular hybrid slotted tunnels. The computer studies are for tunnel working section height to breadth ratios of 0.835 and 0.600 over the Mach number range from 0 to 0.85. Wings swept at 28 deg and 50 deg, with ratios of model span to tunnel breadth varying from 0 to 0.7, are considered. An idealized fuselage shape is used to predict solid and wake blockage corrections for the wall configurations selected on the basis of minimum upwash and curvature interference.
    Keywords: AERODYNAMICS
    Type: Aeronautical Journal (ISSN 0001-9240); 89; 135-148
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  • 67
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    Computational/experimental pressure distributions on a transonic, low-aspect-ratio wing (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 545
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  • 68
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    Experimental and numerical investigation of a shock wave impingement on a cylinder (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 840-846
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  • 69
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    Simulation of rotating stall by the vortex method (1985)
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    Publication Date: 2011-08-19
    Description: The vortex method, coupled to a boundary-layer solver, is applied to the numerical simulation of high Reynolds number incompressible flow in two-dimensional cascades. Periodic conditions are imposed along the plane of the cascade, with several blades per period. Good agreement is found with two finite-difference methods for a single-blade case. When a staggered cascade is treated with five independent blades, the simulation predicts rotating stall, for a range of angles of attack and stagger, and the essential features of the flow are correct. The stall cell steadily propagates along the cascade. The sensitivity of this phenomenon to two parameters is studied, and the stall boundary is found. Quantitative results and visualizations are presented.
    Keywords: AERODYNAMICS
    Type: Journal of Propulsion and Power (ISSN 0748-4658); 1; 235-241
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  • 70
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    Shock-fitting solution of the supersonic flowfield in a rounded internal corner (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 193-200
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  • 71
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    Real-gas flowfields about three-dimensional configurations (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 22; 46-53
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  • 72
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    Transonic solutions for a multielement airfoil using the full-potential equations (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 50-56
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  • 73
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    The influence of leading-edge load alleviation on supersonic wing design (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 71-77
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  • 74
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    Shock-interaction-induced heat transfer to the orbiter wing lower surface (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 22; 516-522
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  • 75
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    Engineering flowfield method with angle-of-attack applications (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 22; 398-404
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  • 76
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    Flowfield investigation of a supercruise fighter model (1985)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 289-295
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  • 77
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    Review - Computational methods for internal flows with emphasis on turbomachinery (1985)
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    Details
    Publication Date: 2011-08-19
    Description: Current computational methods for analyzing flows in turbomachinery and other related internal propulsion components are presented. The methods are divided into two classes. The inviscid methods deal specifically with turbomachinery applications. Viscous methods, deal with generalized duct flows as well as flows in turbomachinery passages. Inviscid methods are categorized into the potential, stream function, and Euler approaches. Viscous methods are treated in terms of parabolic, partially parabolic, and elliptic procedures. Various grids used in association with these procedures are also discussed.
    Keywords: AERODYNAMICS
    Type: ASME, Transactions, Journal of Fluids Engineering (ISSN 0098-2202); 107; 6-22
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    Numerical study of a ramjet dump combustor flowfield (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 604-611
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  • 79
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    Monotone switches in implicit algorithms for potential equations applied to transonic flows (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 492-498
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  • 80
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    Two-dimensional viscous simulation of inlet/diffuser flows with terminal shocks (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Propulsion and Power (ISSN 0748-4658); 1; 103-108
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  • 81
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    Emmons spot forcing for turbulent drag reduction (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An Emmons spot-generation wind tunnel system has been designed to trigger closely spaced Emmons spots in the spanwise and longitudinal directions of an aerodynamic surface. For certain combinations of generator frequencies and amplitude, hole size, and hole spacing, experimental results indicate smaller turbulence scales and a reduction in skin friction of about 15 percent.
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 155-157
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  • 82
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    Interaction of a turbulent vortex with a lifting surface (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The impulsive noise due to blade-vortex-interaction is analyzing in the time domain for the extreme case when the blade cuts through the center of the vortex core with the assumptions of no distortion of the vortex path or of the vortex core. An analytical turbulent vortex core model, described in terms of the tip aerodynamic parameters, is used and its effects on the unsteady loading and maximum acoustic pressure during the interaction are determined.
    Keywords: AERODYNAMICS
    Type: Anal. of Selected Probl. Involving Vortical Flows; p 18-28
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  • 83
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    On the structure of the turbulent vortex (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The trailing vortex generated by a lifting surface, the structure of its turbulent core and the influence of axial flow within the vortex on its initial persistence and on its subsequent decay are described. Similarity solutions of the turbulent diffusion equation are given in closed form and results are expressed in sufficiently simple terms that the influence of the lifting surface parameters on the length of persistence and the rate of decay of the vortex can be evaluated.
    Keywords: AERODYNAMICS
    Type: Anal. of Selected Probl. Involving Vortical Flows; p 6-17
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  • 84
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    A tomographic technique for aerodynamics at transonic speeds (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Computer aided tomography (CAT) provides a means of noninvasively measuring the air density distribution around an aerodynamic model. This technique is global in that a large portion of the flow field can be measured. A test of the applicability of CAT to transonic velocities was studied. A hemispherical-nose cylinder afterbody model was tested at a Mach number of 0.8 with a new laser holographic interferometer at the 2- by 2-Foot Transonic Wind Tunnel. Holograms of the flow field were taken and were reconstructed into interferograms. The fringe distribution (a measure of the local densities) was digitized for subsequent data reduction. A computer program based on the Fourier-transform technique was developed to convert the fringe distribution into three-dimensional densities around the model. Theoretical aerodynamic densities were calculated for evaluating and assessing the accuracy of the data obtained from the tomographic method.
    Keywords: AERODYNAMICS
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  • 85
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    Calculation of transonic steady and oscillatory pressures on a low aspect ratio model and comparison with experiment (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Pressure data measured by the British Royal Aircraft Establishment for the AGARD SMP tailplane are compared with results calculated using the transonic small perturbation code XTRAN3S. A brief description of the analysis is given and a recently developed finite difference grid is described. Results are presented for five steady and nine harmonically oscillating cases near zero angle of attack and for a range of subsonic and transonic Mach numbers.
    Keywords: AERODYNAMICS
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  • 86
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    Recent transonic unsteady pressure measurements at the NASA Langley Research Center (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Four semispan wing model configurations were studied in the Transonic Dynamics Tunnel (TDT). The first model had a clipped delta planform with a circular arc airfoil, the second model had a high aspect ratio planform with a supercritical airfoil, the third model has a rectangular planform with a supercritical airfoil and the fourth model had a high aspect ratio planform with a supercritical airfoil. To generate unsteady flow, the first and third models were equipped with pitch oscillation mechanisms and the first, second and fourth models were equipped with control surface oscillation mechanisms. The fourth model was similar in planform and airfoil shape to the second model, but it is the only one of the four models that has an elastic wing structure. The unsteady pressure studies of the four models are described and some typical results for each model are presented. Comparison of selected experimental data with analytical results also are included.
    Keywords: AERODYNAMICS
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  • 87
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    Experimental and analytical investigation of fan flow interaction with downstream struts (1985)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: An investigation which was designed to provide insight into the fundamental aspects of fan rotor-downstream strut interaction was undertaken. High response, miniature pressure transducers were embedded in the rotor blades of an experimental fan rig. Five downstream struts were placed at several downstream locations in the discharge flow annulus of the single-stage machine. Significant interaction of the rotor blade surface pressures with the flow disturbance produced by the downstream struts was measured. Several numerical procedures for calculating the quasi-steady rotor response due to downstream flow obstructions were developed. A preliminary comparison of experimental and calculated fluctuating blade pressures on the rotor blades shows general agreement between the experimental and calculated values.
    Keywords: AERODYNAMICS
    Type: NASA-CR-175756 , NAS 1.26:175756 , IR-1
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  • 88
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    Application of CFD techniques toward the validation of nonlinear aerodynamic models (1985)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Applications of computational fluid dynamics (CFD) methods to determine the regimes of applicability of nonlinear models describing the unsteady aerodynamic responses to aircraft flight motions are described. The potential advantages of computational methods over experimental methods are discussed and the concepts underlying mathematical modeling are reviewed. The economic and conceptual advantages of the modeling procedure over coupled, simultaneous solutions of the gas dynamic equations and the vehicle's kinematic equations of motion are discussed. The modeling approach, when valid, eliminates the need for costly repetitive computation of flow field solutions. For the test cases considered, the aerodynamic modeling approach is shown to be valid.
    Keywords: AERODYNAMICS
    Type: AGARD Unsteady Aerodynamics-Fundamentals and Applications to Aircraft Dynamics; 15 p
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  • 89
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    Recent experiences of unsteady aerodynamic effects on aircraft flight dynamics at high angle of attack (1985)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Recent research is highlighted which was conducted at the NASA Langley Research Center on two high angle-of-attack flight dynamic phenomena which are dominated by unsteady aerodynamic effects: wing rock and tumbling. Studies of wing rock induced by strong vortical flows and tumbling characteristics observed on an advanced configuration are reviewed. Results of wind tunnel experiments are summarized and the aerodynamic mechanisms involved in the phenomena were discussed.
    Keywords: AERODYNAMICS
    Type: AGARD Unsteady Aerodynamics-Fundamentals and Applications to Aircraft Dynamics; 25 p
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  • 90
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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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  • 91
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    Numerical studies of unsteady transonic flow over oscillating airfoil (1985)
    In:  CASI
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    Publication Date: 2017-10-02
    Description: A finite difference solution to the Navier-Stokes equations combined with a time varying grid generation technique was used to compute unsteady transonic flow over an oscillating airfoil. These computations were compared with experimental data (obtained at Ames Research Center) which form part of the AGARD standard configuration for aeroelastic analysis. A variety of approximations to the full Navier-Stokes equations was used to determine the effect of frequency, shock wave motion, flow separation, and airfoil geometry on unsteady pressures and overall air loads. Good agreement is shown between experiment and theory with the limiting factor being the lack of a reliable turbulence model for high Reynolds number, unsteady transonic flows.
    Keywords: AERODYNAMICS
    Type: AGARD Transonic Unsteady Aerodyn. and its Aeroelastic Appl.; 22 p
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  • 92
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    Experience with transonic unsteady aerodynamic calculations (1985)
    In:  CASI
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    Publication Date: 2017-10-02
    Description: Comparisons of calculated and experimental transonic unsteady pressures and airloads for four of the AGARD Two Dimensional Aeroelastic Configurations and for a rectangular supercritical wing are presented. The two dimensional computer code, XTRAN2L, implementing the transonic small perturbation equation was used to obtain results for: (1) pitching oscillations of the NACA 64A010A; NLR 7301 and NACA 0012 airfoils; (2) flap oscillations for the NACA 64A006 and NRL 7301 airfoils; and (3) transient ramping motions for the NACA 0012 airfoils. Results from the three dimensional code XTRAN3S are compared with data from a rectangular supercritical wing oscillating in pitch. These cases illustrate the conditions under which the transonic inviscid small perturbation equation provides reasonable predictions.
    Keywords: AERODYNAMICS
    Type: AGARD Transonic Unsteady Aerodyn. and its Aeroelastic Appl.; 21 p
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  • 93
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    Unsteady transonic aerodynamic and aeroelastic calculations about airfoils and wings (1985)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The development and application of transonic small disturbance codes for computing two dimensional flows, using the code ATRAN2, and for computing three dimensional flows, using the code ATRAN3S, are described. Calculated and experimental results are compared for unsteady flows about airfoils and wings, including several of the cases from the AGARD Standard Aeroelastic Configurations. In two dimensions, the results include AGARD priority cases for the NACA 54A006, NACA 64A010, NACA 0012, and MBB-A3 airfoils. In three dimensions, the results include flow about the F-5 wing, a typical wing, and the AGARD rectangular wings. Viscous corrections are included in some calculations, including those for the AGARD rectangular wing. For several cases, the aerodynamic and aeroelastic calculations are compared with experimental results.
    Keywords: AERODYNAMICS
    Type: AGARD Transonic Unsteady Aerodyn. and its Aeroelastic Appl.; 31 p
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    Status and prospects of computational fluid dynamics for unsteady transonic flow (1985)
    In:  CASI
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    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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    Three dimensional flow phenomena in fluid machinery; Proceedings of the Winter Annual Meeting, Miami Beach, FL, November 17-22, 1985 (1985)
    In:  Other Sources
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    Publication Date: 2016-03-09
    Description: For papers presented in this volume provide an overview of the latest developments in experimental measurements and analytical and numerical predictions of three-dimensional flows in fluid machinery. Topics discussed include three-dimensional cascade testing of turbine nozzles at high exit Mach number; the use of a secondary flow computation in the compressor design process; an experimental investigation of static propeller flow field; and calculation of three-dimensional boundary layers on rotating turbine blades. Papers are also presented on a three-dimensional solution method for turbomachinery analysis; analysis of rotational inviscid flows in curved passages; and a mathematical model for the analysis of fluid flow in a scroll.
    Keywords: AERODYNAMICS
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    Application of a lifting surface theory for a helicopter in forward flight (1985)
    In:  Other Sources
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    Publication Date: 2018-12-01
    Description: A lifting-surface theory has been developed for a helicopter rotor in forward flight for compressible and incompressible flow. The method utilizes the concept of the linearized acceleration potential and makes use of the doublet lattice procedure. Calculations demonstrating the application of the method are given in terms of the lift distribution on a single rotor, a two-bladed rotor, and a rotor with swept-forward and swept-back tips. In addition, the lift on a rotor which is vibrating in a pitching mode at 4/rev is given. Compressibility effects and interference effects for a two-bladed rotor are discussed.
    Keywords: AERODYNAMICS
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    A study of laminar separation bubble in the concave region of an airfoil using laser velocimetry (1985)
    In:  Other Sources
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    Publication Date: 2018-12-01
    Description: Laser velocimetry (LV) was used to study the nature of laminar separation bubbles in the concave region of a 1.83-meter airfoil model which was tested in the NASA Langley Low Turbulence Pressure Tunnel. Three component, coincident data from LV measurements including histograms of particle velocity, mean velocity profiles, turbulence intensity, and Reynolds stresses within the shear layer were used to determine the locations of laminar separation, transition, and turbulent reattachment. boundary-layer parameters determined from velocity profiles were used to compare the results with existing empirical relations for describing the laminar separation bubble.
    Keywords: AERODYNAMICS
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    Propulsion and airframe aerodynamic interactions of supersonic V/STOL configurations, phase 1 (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A wind tunnel model of a supersonic V/STOL fighter configuration has been tested to measure the aerodynamic interaction effects which can result from geometrically close-coupled propulsion system/airframe components. The approach was to configure the model to present two different test techniques. One was a coventional test technique composed of two test modes. In the Flow-Through mode, absolute configuration aerodynamics are measured, including inlet/airframe interactions. In the Jet-Effects mode, incremental nozzle/airframe interactions are measured. The other test technique is a propulsion simulator approach, where a subscale, externally powered engine is mounted in the model. This allows proper measurement of inlet/airframe and nozzle/airframe interactions simultaneously.
    Keywords: AERODYNAMICS
    Type: NASA-CR-177369 , NAS 1.26:177369
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    Acceleration to a steady state for the Euler equations (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A multistage Runge-Kutta method is analyzed for solving the Euler equations exterior to an airfoil. Highly subsonic, transonic and supersonic flows are evaluated. Various techniques for accelerating the convergence to a steady state are introduced and analyzed.
    Keywords: AERODYNAMICS
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    Numerical solution of the Euler equation for compressible inviscid fluids (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: An effort is made to develop a satisfactory numerical method for the calculation of steady solutions of the Euler equations for inviscid compressible gas flows. The intended application is the prediction of the aerodynamic properties of aircraft flying at transonic speeds. Particular consideration is given to the modification of the equations to improve convergence to a steady state; finite volume formulation; adaptive dissipation; schemes designed to improve the resolution of shock waves; hybrid multistage time stepping schemes; residual averaging; a multigrid scheme; and trials with Burgers' equation. Results clearly demonstrate that the convergence of a time-dependent hyperbolic system to a steady state can be substantially accelerated by the introduction of multiple grids.
    Keywords: AERODYNAMICS
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