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  • 1
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    The development of a CFD potential method for the analysis of tilt-rotors (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A new CFD potential code, FPX (eXtended Full-Potential), has been developed for application to both helicopters and tilt-rotors. The code solves the unsteady, three-dimensional full potential equation and is an extension of the rotor code, FPR. Both entropy and viscosity corrections are included to enhance the physical modeling capabilities. A number of efficiency related modifications have yielded a factor of two speed-up in the code. An axial flow capability has been added to treat tilt-rotor in forward flight (cruise mode). In order to employ streamwise periodicity and accurately solve for the propagation of acoustic signals in the tip region, an H-H topology has been added to the basic O-H grid system. Computations are performed for the XV-15 Standard and ATB blades at high-speed conditions. Comparisons are made for the blade aerodynamics and the induced fuselage cabin pressure for a range of Mach numbers. Grid generation, wake treatment, and far-field wall treatment are identified as problem areas with recommendations for future research.
    Keywords: AERODYNAMICS
    Type: In: AHS and Royal Aeronautical Society, Technical Specialists' Meeting on Rotorcraft Acoustics(Fluid Dynamics, Philadelphia, PA, Oct. 15-17, 1991, Proceedings (A93-29401 10-71); 15 p.
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  • 2
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    A detection of the evolutionary time scale of the DA white dwarf G117 - B15A with the Whole Earth Telescope (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The time rate of change for the main pulsation period of the 13,000 K DA white dwarf G117 - B15A has been detected using the Whole Earth Telescope (WET). The observed rate of period change, P(dot) = (12.0 + or - 3.5) x 10 to the -15th s/s, is somewhat larger than the published theoretical calculations of the rate of period change due to cooling, based on carbon core white dwarf models. Other effects that could contribute to the observed rate of period change are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 378; L45-L48
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  • 3
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    Hubble Space Telescope images and follow-up spectroscopy of the Orion nebula (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Recently published HST images of the Orion nebula reveal elephant-trunk structures, an apparent jet of material, and fine-scale structure in the Herbig-Haro object HH2, which is located at the base of an elephant trunk. High-resolution spectroscopy shows that the apparent jet is actually an ionization front seen edge-on. HH2 shows a complex structure in the several stages of ionization observed. There seem to be two velocity systems characterized by a bright central region and an accompanying shell-like emission. These two systems are most likely to be the result of a bow shock and corresponding Mach disk formed from the interaction of a collimated jet and the ambient gas of the nebula.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 103; 824-829
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  • 4
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    The unusual X-ray pulse timing of AE Aquarii (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: X-ray data for AE Aqr are reanalyzed by using a refined analysis technique and different approaches. The results obtained indicate that X-rays are produced at the same site as the optical, and there is no evidence for the direct X-ray beam from the white dwarf. The optical period was found to be the most significant X-ray period. The direct X-ray beam from the white dwarf is at least four times weaker than the pulsed X-ray signal at the optical period. Given the above-mentioned correlations with the optical, it is inferred that the X-ray pulsations must originate at the same target in the orbit responsible for the optical pulsations. There is a possible orbital modulation of the optical pulse-timing and emission-line orbits. It is shown that the X-ray pulse has slipped at least twice in phase by more than 30 percent in two years' time.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 378; 286-292
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  • 5
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    Large-scale advanced propeller blade pressure distributions - Prediction and data (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Propulsion and Power (ISSN 0748-4658); 7; 452-461
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  • 6
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    N III line emission in planetary nebulae - Not Bowen fluorescence (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A direct comparison of photometrically observed line ratios in the N III 4640 and 4100 A multiplets emitted by planetary nebulae with theoretically predicted ratios expected from the postulated Bowen process of selective photoexcitation by an O III resonance line shows that the N III lines are not produced by the Bowen process as has been commonly accepted. This will have consequences for the interpretation of these lines in other astrophysical sources. A further, unexpected result is that the N III level populations involved are found to be essentially in statistical equilibrium. Possible populating mechanisms are briefly discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 381; L59-L62
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  • 7
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    Euler calculations of unsteady transonic flow in cascades (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: In the present paper, Euler calculations of unsteady transonic flow in cascades are presented. A finite volume scheme is used to discretize the equations, which are implemented on a blade-fitted deformable mesh. The space-discretized equations are integrated forward in time using a multistage Runge-Kutta scheme. Adaptive dissipation terms of the type proposed by Jameson and Baker are added to capture shocks and to suppress nonphysical oscillations. Phase-shifted boundary conditions are used to reduce the computational domain to a single reference passage. No assumptions of small amplitudes or small flow deflections are made. Thus, the present code makes it possible to carry out aeroelastic calculations for cases where the shock strengths and oscillation amplitudes exceed the inherent limitations of potential flow codes.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 91-1104
    Format: text
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  • 8
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    Thin-layer and full Navier-Stokes, locally-conical and three-dimensional asymmetric solutions (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The unsteady, compressible thin-layer and full Navier-Stokes equations are used to numerically simulate steady and unsteady asymmetric, supersonic, locally-conical flows around a 5-deg-semiapex angle circular cone. The main computational scheme used for the present computations is the implicit, upwind, flux-difference splitting, finite-volume scheme. Comparisons of the solutions using the two sets of equations are presented for the flow asymmetry and its control. Computational studies are also presented to investigate the effects of the freestream Reynolds number and the locally-scaled Reynolds number on the flow asymmetry. These studies are carried out using the full Navier-Stokes equations. Three-dimensional, asymmetric flow solutions are also presented for a 5-deg-semiapex angle cone of unit length and a cone-cylinder configuration. The three-dimensional solutions are obtained by using the thin-layer equations and short-duration transient side-slip disturbances along with a very fine grid.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 91-0547
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  • 9
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    Experimental investigation of turbulent flow through a circular-to-rectangular transition duct (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Steady, incompressible, turbulent, swirl-free flow through a circular-to-rectangular transition duck was studied experimentally. The cross-sectional area remains the same at the exit as at the inlet, but varies through the transition section to a maximum value approximately 15 percent above the inlet value. The cross-sectional geometry everywhere along the duct is defined by the equation of a superellipse. Mean and turbulence data were accumulated utilizing pressure and hot-wire instrumentation at five stations along the test section. Data are presented for operating bulk Reynolds numbers of 88,000 and 390,000. Measured quantities include total and static pressure, the three components of the mean velocity vector, and the six components of the Reynolds stress tensor. In addition to the transition duct measurements, a hot-wire technique which relies on the sequential use of single rotatable normal and slant-wire probes was proposed. The technique is applicable for measurement of the total mean velocity vector and the complete Reynolds stress tensor when the primary flow is arbitrarily skewed relative to a plane which lies normal to the probe axis of rotation.
    Keywords: AERODYNAMICS
    Type: NASA-TM-105210 , E-6522 , NAS 1.15:105210
    Format: application/pdf
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  • 10
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    Engineering method for aero-propulsive characteristics at hypersonic Mach numbers (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: An engineering method has been developed for the rapid analysis of external aerodynamics and propulsive performance characteristics of airbreathing vehicles at hypersonic Mach numbers. This method, based on the theory of characteristics, has been developed to analyze fuselage-wing body combinations and body flaps with blunt or sharp leading/trailing edges. Arbitrary ratio of specific heat for the flowing medium can be specified in the program. Furthermore, the capability exists in the code to compute the inviscid inlet mass capture and momentum flux. The method is under development for computations of pressure distribution, and flow characteristics in the inlet, along with the effect of viscosity. Correlative studies have been performed for representative hypersonic configurations using the current method. The results of these correlations for various aerodynamics parameters are encouraging.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 91-5061
    Format: text
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