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At least 1,045 records · Page 58

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NASA NTRS1987

A computational analysis of flow separation over five different airfoil geometries at high angles-of-attack

The flux splitting method of Van Leer (1982) and an implicit, upwind-biased, finite-volume scheme of Rumsey (1985) for solving the two-dimensional Reynolds-averaged Navier-Stokes equations were applied to analyze five airfoil geometries (the NACA 0012, 12-percent Joukowski, NACA 4412, NACA 65-015, and LS1-0417 sections), at high angles of attack. The effect of grid density and grid extent on the Strouhal number of the unsteady flow was computed, as well as the effect of variations in Mach number, Reynolds number, and angle of attack. It was found, that past an angle of attack of 20 deg, Strouhal numbers were independent of angle of attack (at a constant value of 0.115), agreeing well with the experimental findings of Tyler (1931).

Rumsey, Christopher L.↗

NASA NTRS1987

Analytical and experimental evaluation of a 3-D hypersonic fixed-geometry, swept, mixed compression inlet

The performance of a fixed-geometry, swept, mixed compression hypersonic inlet is presented. The experimental evaluation was conducted for a Mach number of 6.0 and for several angles of attack. The measured surface pressures and pitot pressure surveys at the inlet throat are compared to computations using a three-dimensional Euler code and an integral boundary layer theory. Unique features of the intake design, including the boundary layer control, insure a high inlet performance. The experimental data show the inlet has a high mass averaged total pressure recovery, a high mass capture and nearly uniform flow diffusion. The swept inlet exhibits excellent starting characteristics, and high flow stability at angle of attack.

Agnone, Anthony M.↗

NASA NTRS1986

Traveling and standing waves in binary-fluid convection in finite geometries

The effect of finite geometry on the competition between traveling waves and standing waves in systems with a Hopf bifurcation to a state with spatial structure is considered in the linear and weakly nonlinear regimes. The spatial structure observed by Kolodner et al. (1986) in binary-fluid convection is explained in terms of the reflection of the linear traveling waves. The reflection coefficient is calculated, and is found to go to zero as the frequency of the waves becomes small. The pattern expected in a saturated nonlinear state is discussed.

Cross, M. C.↗

NASA NTRS1986

The effect of perspective geometry on judged direction in spatial information instruments

Attention is given to the methodology and results of an experiment examining design aspects of panel-mounted displays that (1) incorporate a planar grid in their symbology, (2) subtend a narrow visual angle, and (3) are mounted so that they can be viewed face-on rather than obliquely. An analysis of direction judgments in such perspective displays shows that the perspective geometry of the stimulus image has a significant effect on direction judgment accuracy. Target elevation direction is generally overestimated; azimuth error varies sinusoidally with target azimuth direction, and is modulated by field-of-view angle.

Mcgreevy, Michael Wallace↗

NASA NTRS1987

Ion distributions in a two-dimensional reconnection field geometry

ISEE observations have shown trapped ion distributions in the magnetosphere along with streaming ion distributions in the magnetosheath. The more energetic ion beams are further away from the magnetopause than lower-energy ion beams. Predictions made with a simple two-dimensional reconnection model which contains a neutral line and an azimuthal electric field were compared with the experimental data of Sept., 1978. The model explains trapped particles in the magnetosphere due to nonadiabatic mirroring in the magnetosheath and streaming ions in the magnetosheath due to energization at the magnetopause. The model also shows the higher-energy ions extending further into the magnetosheath and farther away from the magnetopause than the lower-energy ions. This suggests the ion data of Sept., 1978 are consistent with a reconnection geometry.

Curran, D. B.↗

NASA NTRS1987

Effects of non-Maxwellian electron velocity distribution functions and nonspherical geometry on minor ions in the solar wind

A previous model has shown that in order to account for the charge state distribution in the low-speed solar wind, a high coronal temperature is necessary and that this temperature peak goes together with a peak of nx/np in the corona. In the present paper, one of the assumptions made previously, i.e., that coronal electrons are Maxwellian, is relaxed, and a much cooler model is presented, which could account for the same oxygen charge states in the solar wind due to the inclusion of non-Maxwellian electrons. Also, due to a different choice of the coronal magnetic field geometry, this model would show no enhancement of the coronal nx/np. Results of the two models are then compared, and observational tests to distinguish between the two scenarios are proposed: comparison of directly measured coronal Te to charge state measurements in the solar wind, determination of the coronal nx/np measurement of ion speeds in the acceleration region of the solar wind, and measurement of the frozen-in silicon charge state distribution.

Burgi, A.↗

NASA NTRS1987

A versatile and low order hybrid stress element for general shell geometry

A hybrid stress general shell element is developed based on the Hellinger-Reissner principle modified for relaxed element compatibility conditions. The element is based on a consistent first order thin shell theory with Love Kirchhoff hypotheses. It is of quadrilateral shape with only four corner nodes and five degrees of freedom per node. The geometry of the element is approximated through a bi-cubic polynomial surface patch. Numerical examples consist of torsion-loaded slit cylinder and pinched cylinder with open ends and rigid diaphragmed ends. Also, the representation of the rigid body motion is studied by series of parametric eigenvalue analysis of the stiffness matrix.

Kang, David S.↗

NASA NTRS1986

Wind deflection compensated, zero-coma telescope truss geometries

Six telescope truss geometries are evaluated for both wind and gravity deflection stiffness. The existence of simultaneous solutions for gravity and wind deflections is demonstrated. A baseline design for the Texas 7.6-meter telescope with an F/1.4 Angel lightweight borosilicate primary mirror is shown.

Meinel, Aden B.↗

NASA NTRS1987

Noncommutative-geometry model for closed bosonic strings

It is shown how Witten's (1986) noncommutative geometry may be extended to describe the closed bosonic string. For closed strings, an explicit representation is provided of the integral operator needed to construct an action and of an associative product on string fields. The proper choice of the action of the integral operator and the associative product in order to give rise to a reasonable theory is explained, and the consequences of such a choice are discussed. It is shown that the ghost numbers of the operator and associative product can be chosen arbitrarily for both open and closed strings, and that this construct can be used as an action for interacting closed bosonic strings.

Sen, Siddhartha↗

NASA NTRS1987

Grid generation and inviscid flow computation about cranked-winged airplane geometries

An algebraic grid generation procedure that defines a patched multiple-block grid system suitable for fighter-type aircraft geometries with fuselage and engine inlet, canard or horizontal tail, cranked delta wing and vertical fin has been developed. The grid generation is based on transfinite interpolation and requires little computational power. A finite-volume Euler solver using explicit Runge-Kutta time-stepping has been adapted to this grid system and implemented on the VPS-32 vector processor with a high degree of vectorization. Grids are presented for an experimental aircraft with fuselage, canard, 70-20-cranked wing, and vertical fin. Computed inviscid compressible flow solutions are presented for Mach 2 at 3.79, 7 and 10 deg angles of attack. Conmparisons of the 3.79 deg computed solutions are made with available full-potential flow and Euler flow solutions on the same configuration but with another grid system. The occurrence of an unsteady solution in the 10 deg angle of attack case is discussed.

Eriksson, L.-E.↗

NASA NTRS1987

Small Al clusters. I - The effect of basis set and correlation on the geometry of small Al clusters

A detailed study is presented of the basis set requirements and effects of correlation on the geometry and structure of small Al(n) clusters n = 2, 4, and 13. An effective core potential (ECP) is developed from the Huzinaga basis which accurately reproduces the all-electron results. It is found that depolarization functions are very important in computing the bond length, and that the bond contraction obtained is about as large for a 13-atom cluster as for the Al(4) rhombus structure. With d functions on each center in Al(13), a bond distance shorter than the bulk is obtained, as expected. The inclusion of correlation in Al(4) is found to be less important than the addition of polarization functions for determining the bond length, but increases substantially the calculated atomization energy. These calibration calculations allow an accurate treatment for Al(n) clusters to be designed.

Bauschlicher, Charles W., Jr.↗

NASA NTRS1987

Effect of nozzle geometry on the resistojet exhaust plume

Five nozzle configurations were used to study the effect of geometry on the plume structure of a resistojet exhausting into a vacuum. Mass flux data in the forward and back flux regions were obtained with a cryogenically cooled quartz crystal microbalance. The propellant used was CO2 at 300 K and a mass flow rate of 0.2 g/s. The data reveal that the percent of mass flow contained within half angles of 10, 30, and 40 deg varied by less than 12 percent from a standard 20 deg half-angle cone nozzle.

Breyley, Loranell↗

NASA NTRS1987

A FORTRAN code for the calculation of probe volume geometry changes in a laser anemometry system caused by window refraction

A computer code was written which utilizes ray tracing techniques to predict the changes in position and geometry of a laser Doppler velocimeter probe volume resulting from refraction effects. The code predicts the position change, changes in beam crossing angle, and the amount of uncrossing that occur when the beams traverse a region with a changed index of refraction, such as a glass window. The code calculates the changes for flat plate, cylinder, general axisymmetric and general surface windows and is currently operational on a VAX 8600 computer system.

Owen, Albert K.↗

NASA NTRS1986

Application of a full potential method for analysis of complex aircraft geometries

A supersonic potential flow solver was developed to analyze the flow over complex realistic aircraft geometries. Enhancements to the method were made to accommodate regions of subsonic flow, the effect of trailing wakes on other aircraft components, and the modeling/gridding of complete configurations. Validation of the method was demonstrated by comparisons with experimental aerodynamic force and surface pressure measurements. The predicted results are in very good agreement with the experimental data. The bibliography contains additional information on the use of the potential flow code to predict the aerodynamics of high-speed wing/body configurations, waverider concepts, TAV, and the Space Shuttle orbiter package.

Jones, Kenneth M.↗

NASA NTRS1987

Shock structure in jets of arbitrary exit geometry

The shock structure and hydrodynamic stability of single and twin jets with arbitrary exit geometry are studied. Both vortex sheets and realistic mean profiles are considered for the jet shear layer. The boundary element method is used to predict the shock spacing and screech tones in a vortex sheet model of a single jet. Results are given for circular, elliptic and rectangular jets and the results compared with analysis and experiment. A finite difference technique is used to examine the effect of finite mixing layer thickness for a single jet. The hydrodynamic stability of twin circular jets is also considered. The variation of the stability characteristics are presented for the vortex sheet case for several separation distances. The formulation of the problem to account for finite thickness effects is also given.

Morris, P. J.↗

NASA NTRS1987

Ring geometry on Ganymede and Callisto

Geometrical considerations are brought to bear on a discussion of the impact and internal origin scenarios for the major furrow system of Ganymede, which was remapped in order to take advantage of improvements in coordinate control. Furrow occurrence and geometry are judged to be consistent with an impact origin; the perceived current nonalignment of the presumably once-concentric furrows may be adduced as evidence for large-scale lateral motion of dark terrain blocks in Ganymede's crust, in association with bright terrain formation.

Schenk, Paul M.↗

NASA NTRS1987

Effects of forebody geometry on subsonic laminar boundary layer stability

The effect of forebody geometry on the stability of the laminar boundary layer on axisymmetric body shapes at Reynolds numbers typical of small and medium sized aircraft in low-subsonic cruise flight is investigated. It is found that small nose radii are important in obtaining n-factors of 9 on axisymmetric bodies of fineness ratio of about 6 at large nondimensional axial distances downstream. Results for the effect of the steepness of the pressure gradient and the value of the minimum pressure on the extent of laminar flows on an axisymmetric body at a given Reynolds number are also presented.

Dodbele, S. S.↗

NASA NTRS1988

CSDUST3 - A radiation transport code for a dusty medium with 1-D planar, spherical or cylindrical geometry

The program solves the radiation transport problem in a dusty medium with one-dimensional planar, spherical or cylindrical geometry. It determines self-consistently the effects of multiple scattering, absorption, and re-emission of photons on the temperature of dust grains and the characteristics of the internal radiation field. The program can treat radiation field anisotropy, linear anisotropic scattering, and multi-grain components. The program output consists of the dust-temperature distribution, flux spectrum, surface brightness at each frequency and the observed intensities (involving a convolution with a telescope beam pattern).

Egan, Michael P.↗