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  • Inorganic Chemistry  (83,671)
  • AERODYNAMICS  (12,790)
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  • 11
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    Identification of aerodynamic coefficients using computational neural networks (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Keywords: AERODYNAMICS
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 16; 6; p. 1018-1025.
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    NASA TECHNICAL REPORTS
  • 12
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    Development of the wake behind a circular cylinder impulsively started into rotatory and rectilinear motion (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The temporal development of a 2D viscous incompressible flow generated by a circular cylinder started impulsively into steady rotatory and rectilinear motion is studied by integration of a velocity/vorticity formulation of the governing equations, using an explicit finite-difference/pseudo-spectral technique and an implementation of the Biot-Savart law. Results are presented for a Reynolds number of 200 (based on the cylinder diameter 2a and the magnitude U of the rectilinear velocity) for several values of the angular/rectilinear speed ratio alpha = omega(a)/U (where omega is the angular speed) up to 3.25. Several aspects of the kinematics and dynamics of the flow not considered earlier are discussed. For higher values of alpha, the results indicate that for Re = 200, vortex shedding does indeed occur for alpha = 3.25. However, consecutive vortices shed by the body can be shed from the same side and be of the same sense, in contrast to the nonrotating case, in which mirror-image vortices of opposite sense are shed alternately on opposite sides of the body. The implications of the results are discussed in relation to the possibility of suppressing vortex shedding by open or closed-loop control of the rotation rate.
    Keywords: AERODYNAMICS
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); p. 449-484.
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    NASA TECHNICAL REPORTS
  • 13
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    A time-accurate high-resolution TVD scheme for solving the Navier-Stokes equations (1993)
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    Publication Date: 2019-08-28
    Description: A total variation diminishing (TVD) scheme has been developed and incorporated into an existing time-accurate high-resolution Navier-Stokes code. The accuracy and the robustness of the resulting solution procedure have been assessed by performing many calculations in four different areas: shock tube flows, regular shock reflection, supersonic boundary layer, and shock boundary layer interactions. These numerical results compare well with corresponding exact solutions or experimental data.
    Keywords: AERODYNAMICS
    Type: Computers & Fluids (ISSN 0045-7930); 22; 5-Apr; p. 517-528.
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    NASA TECHNICAL REPORTS
  • 14
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    Viscous and inviscid instabilities of a trailing vortex (1992)
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    Publication Date: 2019-08-28
    Description: The linear stability of the trailing line vortex model of Batchelor (1964) is studied using a spectral collocation and matrix eigenvalue method. The entire unstable region in the swirl/axial wavenumber parameter space is mapped out for various azimuthal wavenumbers for both the inviscid and viscous stability problem. The results of the study provide a direct numerical validation of the large-azimuthal-wavenumber asymptotic analysis of Leibovich and Stewartson (1983). It is shown that accurate results are obtained up to azimuthal wavenumbers of 10,000 and greater, and the agreement with the asymptotic theory is excellent.
    Keywords: AERODYNAMICS
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); p. 91-114.
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  • 15
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    Exploratory study of wall pressure fluctuations in a Mach 5, sharp fin-induced turbulent interaction (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 30; 9 Se; 2188-219
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  • 16
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    A new approach for the calculation of transitional flows (1992)
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    Publication Date: 2019-08-28
    Description: In spite of many attempts at modeling natural transition, it has not been possible to predict the streamwise intensities. A procedure is developed which incorporates some results of linear stability theory into one-equation and stress model formulations. The stresses resulting from fluctuations in the transitional region have turbulent, laminar (nonturbulent) and large eddy components. Comparison with Schubauer and Klebanoff's experiments have shown that the nonturbulent and large eddy components have a large influence on the streamwise intensities and little influence on the shear stress. Finally, predictions of the one-equation model were as good as those obtained by the stress model.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 92-2669 , AIAA Applied Aerodynamics Conference; Jun 22, 1992 - Jun 24, 1992; Palo Alto, CA; United States
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  • 17
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    Numerical simulations of upstream blocking, columnar disturbances, and bores in stably stratified shear flows over an obstacle (1994)
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    Publication Date: 2019-08-28
    Description: A two-dimensional, nonhydrostatic, elastic numerical model has been used to study the generation of gravity waves for a stably stratified shear flow over an obstacle. When a low-level wind shear is included in the simulation, we find that the predictions for noticeable upstream effects based on Froude number for a uniform flow are no longer accurate. Upstream effects are encountered in the form of upstream propagating columnar disturbances and internal bores away from the obstacle. The limited parameter space studies conducted in this study suggest that the ratio of the shear depth to the obstacle heigh (d/H), the obstacle aspect ratio (H/L), and the Froude number (U/NH) are instrumental in determining the strength and the existence of these upstream disturbances. Thus, the present theoretical and empirical understanding of the importance of the Froude number for determining the nature of upstream effects should be modified substantially to include additional nondimensional parameters when shear is present.
    Keywords: AERODYNAMICS
    Type: Monthly Weather Review (ISSN 0027-0644); 122; 11; p. 2506-2529
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  • 18
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    Aerothermodynamic heating due to shock wave/laminar boundary-layer interactions in high-enthalpy hypersonic flow (1993)
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    Publication Date: 2019-08-28
    Description: The interaction between a swept shock wave and a laminar boundary layer was investigated experimentally in high-enthalpy hypersonic flow. The effect of high-temperature, real gas physics on the interaction was examined by conducting tests in air and helium. Heat transfer measurements were made on the surface of a flat plate and a shock-generating fin using thin-film resistance sensors for fin incidence angles of 0, 5, and 10 deg at Mach numbers of 6.9 in air and 7.2 in helium. The experiments were conducted in the NASA HYPULSE expansion tube, an impulse-type facility capable of generating high-enthalpy, high-velocity flow with freestream levels of dissociated species that are particularly low. The measurements indicate that the swept shock wave creates high local heat transfer levels in the interaction region, with the highest heating found in the strongest interaction. The maximum measured heating rates in the interaction are order of magnitude greater than laminar flat plate boundary layer heating levels at the same location.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 93-3135 , AIAA, Fluid Dynamics Conference; Jul 06, 1993 - Jul 09, 1993; Orlando, FL; United States|; 12 p.
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  • 19
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    Flow field measurements in a crossing shockwave turbulent boundary layer interaction at Mach 3 (1993)
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    Publication Date: 2019-08-28
    Description: An experimental study has been conducted to examine the flow field of the 3D crossing shock wave/turbulent boundary layer interaction. A symmetric pair of 9-deg fins were used to generate the crossing shocks. The incoming boundary layer was developed on the tunnel sidewall and thus was relatively thick, 0.49 arcsec, and suited for pitot probe surveys. The test conditions were a nominal Mach number of 3 and unit Reynolds number of 1.2 x 10 exp 7/ft. The measurements obtained included surface oil flow visualizations, surface static pressures, and boundary layer pitot pressure profiles. The results showed that downstream of the crossing shock intersection, the stagnation pressure losses were significant and the stagnation pressure profiles were highly nonuniform. Despite the severe shock disturbances, the law of the wall and the law of the wake were found to give relatively good agreement with the experimental data.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 93-3434 , In: AIAA Applied Aerodynamics Conference, 11th, Monterey, CA, Aug. 9-11, 1993, Technical Papers. Pt. 1 (A93-47201 19-02); p. 290-300.
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  • 20
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    Nonequilibrium effects on the aerothermodynamics of transatmospheric and aerobraking vehicles (1993)
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    Publication Date: 2019-08-28
    Description: A 3D CFD algorithm is used to study the effect of thermal and chemical nonequilibrium on slender and blunt body aerothermodynamics. Both perfect gas and reacting gas air models are used to compute the flow over a generic transatmospheric vehicle and a proposed lunar transfer vehicle. The reacting air is characterized by a translational-rotational temperature and a vibrational-electron-electronic temperature and includes eight chemical species. The effects of chemical reaction, vibrational excitation, and ionization on lift-to-drag ratio and trim angle are investigated. Results for the NASA Ames All-body Configuration show a significant difference in center of gravity location for a reacting gas flight case when compared to a perfect gas wind tunnel case at the same Mach number, Reynolds number, and angle of attack. For the same center of gravity location, the wind tunnel model trims at lower angle of attack than the full-scale flight case. Nonionized and ionized results for a proposed lunar transfer vehicle compare well to computational results obtained from a previously validated reacting gas algorithm. Under the conditions investigated, effects of weak ionization on the heat transfer and aerodynamic coefficients were minimal.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 93-2837 , AIAA, Thermophysics Conference; Jul 06, 1993 - Jul 09, 1993; Orlando, FL; United States|; 11 p.
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