Search NASA⌕ Search

SEARCH · Search NASA

Results for “Aerodynamics”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

An initial look at the supersonic aerodynamics of twin-fuselage aircraft concepts

Results of two studies into the supersonic aerodynamics of twin-fuselage aircraft configurations are summarized. In the first study, a set of experimental data was obtained on a simple rectangular-wing twin-fuselage wind-tunnel model; this data was then used to evaluate prediction methods, assess favorable interference effects, and identify any unexpected or unpredictable aerodynamic phenomena. Results are presented which show that significant reductions in wave drag are possible through optimum body positioning and that existing aerodynamic prediction methods are adequate for making preliminary aerodynamic estimates. Several configuration concepts were theoretically explored in the second study, and results are presented which indicate the sensitivity of the twin-fuselage concept to various methods of integrating the aircraft components.

Wood, R. M.↗
NASA NTRS1983

Uniaxial aerodynamic attitude control of artificial satellites

Within the context of a simple mechanical model the paper examines the movement of a satellite with respect to the center of masses under conditions of uniaxial aerodynamic attitude control. The equations of motion of the satellite take account of the gravitational and restorative aerodynamic moments. It is presumed that the aerodynamic moment is much larger than the gravitational, and the motion equations contain a large parameter. A two-parameter integrated surface of these equations is constructed in the form of formal series in terms of negative powers of the large parameter, describing the oscillations and rotations of the satellite about its lengthwise axis, approximately oriented along the orbital tangent. It is proposed to treat such movements as nominal undisturbed motions of the satellite under conditions of aerodynamic attitude control. A numerical investigation is made for the above integrated surface.

Sazonov, V. V.↗
NASA NTRS1983

Aerodynamic investigation of closely coupled lifting surfaces with positive and negative stagger for general aviation applications

Aerodynamic closely coupled lifting surfaces were investigated for both conventional tail aft configurations and canard configurations to determine whether positive stagger or negative stagger had more attractive aerodynamic characteristics. An inviscid multi-element vortex panel program was used in conjunction with a momentum integral boundary layer program to predict two-dimensional aerodynamic characteristics. A multi-element vortex lattice program was used for three-dimensional characteristics. Pressure distributions, transition location, momentum thickness, two- and three-dimensional drag, and boundary layer separation were compared for the positive and negative stagger case. For staggers less than six the results demonstrated that positive stagger configurations are aerodynamically superior.

Selberg, B. P.↗
NASA NTRS1983

Effects of viscosity on transonic-aerodynamic and aeroelastic characteristics of oscillating airfoils

Studies were made to investigate the effects of viscosity on aerodynamic and aeroelastic characteristics of oscillating airfoils. The computer code LTRAN2 (viscous), which is based on a small disturbance aerodynamic theory, was used to make aerodynamic computations. Two viscous models, the viscous-ramp model and the lag-entrainment model were considered. The unsteady viscous effects were obtained by use of the quasi-steady assumptions. Two cases, a conventional airfoil, NACA 64A010, and a supercritical airfoil, MBB-A3, were studied at Mach numbers 0.796 and 0.7557, respectively. For both the airfoils, steady and unsteady aerodynamic computations were made by using inviscid and viscous theories. The steady and the unsteady results for the NACA 64A010 airfoil and the steady results for the MBB-A3 airfoil were compared with the available wind-tunnel results. Flutter speeds were computed for both airfoils by using the U-g method and the effects of viscosity on the airfoils were studied. Results from the viscous methods show improvements over the inviscid method.

Guruswamy, P.↗
NASA NTRS1983

Computational aerodynamics applications to transport aircraft design

Examples are cited in assessing the effect that computational aerodynamics has had on the design of transport aircraft. The application of computational potential flow methods to wing design and to high-lift system design is discussed. The benefits offered by computational aerodynamics in reducing design cost, time, and risk are shown to be substantial.These aerodynamic methods have proved to be particularly effective in exposing inferior or poor aerodynamic designs. Particular attention is given to wing design, where the results have been dramatic.

Henne, P. A.↗
NASA NTRS1983

A review of preflight estimates of real-gas effects on space shuttle aerodynamic characteristics

Preflight estimates of the hypersonic aerodynamic characteristics of the Shuttle orbiter were based on a diverse series of research studies using state of the art techniques developed by basic research in the 60's and 70's. Real-gas viscous calculations on simple shapes that were used to evaluate correlation parameters indicated that real-gas effects reduce aerodynamic forces and moments. Inviscid calculations on winged lifting shapes indicated reduced forces and a slight nose-up pitch resulted because of real-gas effects. Analysis of the extensive wind tunnel data base indicated viscous correlation parameters provided the most appropriate extrapolation technique for estimating flight aerodynamics. Variations because of changes in the ratio of specific heats, which was the only available experimental tool for evaluating real-gas effects, indicated that reduced loads and nose-up pitching moments would occur at high altitudes and Mach numbers but that the values would not exceed the tolerances and variations established about the aerodynamic design data book values derived from viscous correlations. During STS-1, nose-up pitching moments exceeded the established variations.

Woods, W. C.↗
NASA NTRS1984

Application of supercomputers to computational aerodynamics

Computers are playing an increasingly important role in the field of aerodynamics such that they now serve as a major complement to wind tunnels in aerospace research and development. Factors pacing advances in computational aerodynamics are identified, including the amount of computational power required to take the next major step in the discipline. Example results obtained from the successively refined forms of the governing equations are discussed, both in the context of levels of computer power required and the degree to which they either further the frontiers of research or apply to problems of practical importance. Finally, the Numerical Aerodynamic Simulation (NAS) Program - with its 1988 target of achieving a sustained computational rate of 1 billion floating point operations per second and operating with a memory of 240 million words - is discussed in terms of its goals and its projected effect on the future of computational aerodynamics.

Peterson, V. L.↗
NASA NTRS1982

Study of aerodynamic technology for single-cruise-engine V/STOL fighter/attack aircraft

A viable, single engine, supersonic V/STOL fighter/attack aircraft concept was defined. This vectored thrust, canard wing configuration utilizes an advanced technology separated flow engine with fan stream burning. The aerodynamic characteristics of this configuration were estimated and performance evaluated. Significant aerodynamic and aerodynamic propulsion interaction uncertainties requiring additional investigation were identified. A wind tunnel model concept and test program to resolve these uncertainties and validate the aerodynamic prediction methods were defined.

Hess, J. R.↗
NASA NTRS1984

Computational aerodynamics and artificial intelligence

The general principles of artificial intelligence are reviewed and speculations are made concerning how knowledge based systems can accelerate the process of acquiring new knowledge in aerodynamics, how computational fluid dynamics may use expert systems, and how expert systems may speed the design and development process. In addition, the anatomy of an idealized expert system called AERODYNAMICIST is discussed. Resource requirements for using artificial intelligence in computational fluid dynamics and aerodynamics are examined. Three main conclusions are presented. First, there are two related aspects of computational aerodynamics: reasoning and calculating. Second, a substantial portion of reasoning can be achieved with artificial intelligence. It offers the opportunity of using computers as reasoning machines to set the stage for efficient calculating. Third, expert systems are likely to be new assets of institutions involved in aeronautics for various tasks of computational aerodynamics.

Mehta, U. B.↗
NASA NTRS1984

Computational aerodynamics and artificial intelligence

Some aspects of artificial intelligence are considered and questions are speculated on, including how knowledge-based systems can accelerate the process of acquiring new knowledge in aerodynamics, how computational fluid dynamics may use 'expert' systems and how expert systems may speed the design and development process. The anatomy of an idealized expert system called AERODYNAMICIST is discussed. Resource requirements are examined for using artificial intelligence in computational fluid dynamics and aerodynamics. Considering two of the essentials of computational aerodynamics - reasoniing and calculating - it is believed that a substantial part of the reasoning can be achieved with artificial intelligence, with computers being used as reasoning machines to set the stage for calculating. Expert systems will probably be new assets of institutions involved in aeronautics for various tasks of computational aerodynamics.

Kutler, P.↗
NASA NTRS1984

Estimated low-speed aerodynamic parameters of an advanced fighter from flight and wind tunnel data

A procedure for determination of aerodynamic model structure and estimation of aerodynamic parameters is applied to data from a modern fighter operating within an angle of attack range of 5 to 60 deg. The paper briefly describes the airplane, flight and wind tunnel data available, postulated models for airplane aerodynamic coefficients and flight data analysis. The results presented contain only a small number of selected longitudinal and lateral parameters. These parameters were obtained from various maneuvers and subsets of joined data from several flights. The estimated parameters are in good agreement with the wind tunnel measurements. The resulting aerodynamic model equations seem to be satisfactory for the prediction of airplane motion.

Klein, V.↗
NASA NTRS1985

Nonlinear problems in flight dynamics involving aerodynamic bifurcations

Aerodynamic bifurcation is defined as the replacement of an unstable equilibrium flow by a new stable equilibrium flow at a critical value of a parameter. A mathematical model of the aerodynamic contribution to the aircraft's equations of motion is amended to accommodate aerodynamic bifurcations. Important bifurcations such as, the onset of large-scale vortex-shedding are defined. The amended mathematical model is capable of incorporating various forms of aerodynamic responses, including those associated with dynamic stall of airfoils.

Tobak, M.↗
NASA NTRS1985

Determination of rarefied-flow aerodynamics of the Shuttle orbiter from flight measurements on STS-6 and STS-7

This report presents the flight data results from the High Resolution Accelerometer Package (HiRAP) experimment on the sixth and seventh Shuttle missions (i.e. STS-6 and STS-7). The data have been reduced to produce aerodynamic force coefficients, principally L/D in the rarefied flow regime. Also, a technique is used to extract approximate body-axis aerodynamic coefficients from the flight data. Comparisons of the rarefied transition flow aerodynamic behavior between the two sets of flight data indicate differences, primarily in the free-molecule flow coefficients; i.e. STS-7 shows a free-molecule flow behavior which correlates with diffuse surface reflection conditions, while STS-6 does not. The data have also been used to estimate the density profiles in the atmosphere. The atmospheric density is generated from 60 to 160 km from each flight. The density profiles produced have a primary wave structure and differences are observed between the two sets of flight data. A new rarefied transitional flow aerodynamic bridging formula has been generated from the flight data. Comparisons with the flight bridging formula and existing Monte Carlo and wind-tunnel data are made.

Blanchard, R. C.↗
NASA NTRS1985

Influence of various unsteady aerodynamic models on the aeromechanical stability of a helicopter in ground resonance

The aeromechanical stability of a helicopter in ground resonance was analyzed, by incorporating five different aerodynamic models in the coupled rotor/fuselage analysis. The sensitivity of the results to changes in aerodynamic modelling was carefully examined. The theoretical results were compared with experimental data and useful conclusions are drawn regarding the role of aerodynamic modeling on this aeromechanical stability problem. The aerodynamic model which provided the best all around correlation with the experimental data was identified.

Friedmann, P. P.↗
NASA NTRS1985

Nonlinear problems in flight dynamics involving aerodynamic bifurcations

Aerodynamic bifurcation is defined as the replacement of an unstable equilibrium flow by a new stable equilibrium flow at a critical value of a parameter. A mathematical model of the aerodynamic contribution to the aircraft's equations of motion is amended to accommodate aerodynamic bifurcations. Important bifurcations such as, the onset of large-scale vortex shedding are defined. The amended mathematical model is capable of incorporating various forms of aerodynamic responses, including those associated with dynamic stall of airfoils.

Murray Tobak↗
NASA NTRS1985

Analysis of holographic interferograms of aerodynamic models in a wind tunnel

Holographic interferometry provides a non-invasive technique for estimating variations in the air density distribution around aerodynamic models in wind tunnels. The testing of this technique has been underway for some time and has been reported previously for a two dimensional aerodynamic model. Results obtained from tests using three dimensional aerodynamic models are summarized. Holograms were made of aerodynamic models in a wind tunnel. Interferograms were made from these holograms. The interference fringes in these holographic interferograms were digitized and this information was entered into the HOLOFT program. The HOLOFT program successfully calculated the known stagnation air density at the nose of a model and the known air density distribution across the cross section passing through the stagnation point for the axisymmetrical case of this model at a Mach number of 0.8. Thus the technique of holographic interferometry does work.The HOLOFT program stands for HOLOgraphic Inversion by 2-D Fourier Transform.

Perry, R. L.↗
NASA NTRS1985

A new look at arbitrary motion unsteady aerodynamics and its application to rotary-wing aeroelasticity

Research on arbitrary motion unsteady aerodynamics, emphasizing applications to rotary wing aeroelastic problems, is reviewed. Generalization of Greenberg's theory and its application to hingeless rotor aeroelastic stability; a technique for formulating finite state approximations to unsteady aerodynamic theories, suitable for fixed and rotary-wing applications, and its application to generalize Loewy's theory; comparison of fixed wing and rotary wing indicial response functions; influence of arbitrary motion aerodynamics, as represented by dynamic inflow on a helicopter in ground resonance; and comparison of dynamic inflow with arbitrary motion unsteady airfoil aerodynamics are covered.

Friedmann, P. P.↗
NASA NTRS1984

Influence of various unsteady aerodynamic models on the aeromechanical stability of a helicopter in ground resonance

The aeromechanical stability of a helicopter in ground resonance was analyzed, by incorporating five different aerodynamic models in the coupled rotor/fuselage analysis. The sensitivity of the results to changes in aerodynamic modelling was carefully examined. The theoretical results were compared with experimental data and useful conclusions are drawn regarding the role of aerodynamic modeling on this aeromechanical stability problem. The aerodynamic model which provided the best all around correlation with the experimental data was identified.

Friedmann, P. P.↗