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NASA NTRS1973

Optimization of wave cancellation in variable porosity transonic wind tunnel flows

A technique has been developed which is capable of determining the optimum wall configuration for a variable porosity perforated wall transonic wind tunnel. The technique is based on a mathematical model arrived at by considering the results of theory and past experimental investigations. A performance index was determined as a function of the significant wind tunnel parameters by comparing a formulation of this mathematical model, using MSFC 14 inch Trisonic Wind Tunnel experimental results, to interference free results. The resulting relationship was then used to determine the combination of wind tunnel parameters which should yield minimum reflected wave interference. A theoretical development of wall porosity requirements for thick wall inclined hole test sections is included which follows the trends and generally the magnitude of available experimental data. This theory is useful in studying the present variable porosity case, but also should be of value in studies concerning the wave cancellation process for fixed porosity walls.

Davis, J. W.↗

NASA NTRS1973

A parallel variable metric optimization algorithm

An algorithm, designed to exploit the parallel computing or vector streaming (pipeline) capabilities of computers is presented. When p is the degree of parallelism, then one cycle of the parallel variable metric algorithm is defined as follows: first, the function and its gradient are computed in parallel at p different values of the independent variable; then the metric is modified by p rank-one corrections; and finally, a single univariant minimization is carried out in the Newton-like direction. Several properties of this algorithm are established. The convergence of the iterates to the solution is proved for a quadratic functional on a real separable Hilbert space. For a finite-dimensional space the convergence is in one cycle when p equals the dimension of the space. Results of numerical experiments indicate that the new algorithm will exploit parallel or pipeline computing capabilities to effect faster convergence than serial techniques.

Straeter, T. A.↗

NASA NTRS1973

Distributions of eight meteorological variables at Cape Kennedy, Florida and Vandenberg Air Force Base, California

Extreme values, median values, and nine percentile values are tabulated for eight meteorological variables at Cape Kennedy, Florida and at Vandenberg Air Force Base, California. The variables are temperature, relative humidity, station pressure, water vapor pressure, water vapor mixing ratio, density, and enthalpy. For each month eight hours are tabulated, namely, 0100, 0400, 0700, 1000, 1300, 1600, 1900, and 2200 local time. These statistics are intended for general use for the space shuttle design trade-off analysis and are not to be used for specific design values.

Graves, M. E.↗

NASA NTRS1973

Galactic gamma rays: Models involving variable cosmic-ray density

Mathematical models were developed to determine variable cosmic ray flux around the galactic plane. Data indicate point sources, molecular hydrogen concentration, increased cosmic ray density toward the galactic center, and neutral pion production combine to cause radiation density variables in the galactic plane.

Strong, A. W.↗

NASA NTRS1973

Data for first NASA Atmospheric Variability Experiment (AVE 1). Part 1: Data tabulation

A tablulation is given of rawinsonde data for NASA's first Atmospheric Variability Experiment (AVE 1) conducted during the period February 19-22, 1964. Methods of data handling and processing, and estimates of error magnitudes are also given. Data taken on the AVE 1 project in 1964 enabled an analysis of a large sector of the eastern United States on a fine resolution time scale. This experiment was run in February 1964, and data were collected as a wave developed in the East Gulf on a frontal system which extended through the eastern part of the United States. The primary objective of AVE 1 was to investigate the variability of parameters in space and over time intervals of three hours, and to integrate the results into NASA programs which require this type of information. The results presented are those from one approach, and represent only a portion of the total research effort that can be accomplished.

Scoggins, J. R.↗

NASA NTRS1973

Variable conductance heat pipe technology

Research and development programs in variable conductance heat pipe technology were conducted. The treatment has been comprehensive, involving theoretical and/or experimental studies in hydrostatics, hydrodynamics, heat transfer into and out of the pipe, fluid selection, and materials compatibility, in addition to the principal subject of variable conductance control techniques. Efforts were not limited to analytical work and laboratory experimentation, but extended to the development, fabrication and test of spacecraft hardware, culminating in the successful flight of the Ames Heat Pipe Experiment on the OAO-C spacecraft.

Marcus, B. D.↗

NASA NTRS1974

Experimental investigation of model variable-geometry and ogee tip rotors

An experimental investigation was conducted to systematically explore the effects of inter-blade spatial relationships and pitch variations on rotor performance and wake geometry. Variable-geometry rotors consisting of various combinations of blade length, axial spacing, azimuth spacing, and collective pitch were tested at model scale in hover and forward flight. In addition, a hover test of a model rotor with an ogee blade tip design was conducted to determine its performance and wake characteristics. The results of this investigation indicate that properly selected variable geometry rotor configurations can offer substantial improvements in hover performance without adversely affecting forward flight performance. Axial spacing of alternate blades was found to provide the greatest performance benefit, and further improvements were achieved by combining azimuth spacing with axial spacing. The performance benefit appears to be related to the relief of local adverse aerodynamic phenomena produced by vortex interference. The ogee tip design was found to substantially reduce the concentrated core intensity of the tip vortex, and could thus prove beneficial for the relief of blade-vortex interaction problems. However, the ogee tip was found to reduce hover performance at model scale.

Landgrebe, A. J.↗

NASA NTRS1974

Computer program for calculation of real gas turbulent boundary layers with variable edge entropy

A user's manual for a computer program which calculates real gas turbulent boundary layers with variable edge entropy on a blunt cone or flat plate at zero angle of attack is presented. An integral method is used. The method includes the effect of real gas in thermodynamic equilibrium and variable edge entropy. A modified Crocco enthalpy velocity relationship is used for the enthalpy profiles and an empirical correlation of the N-power law profile is used for the velocity profile. The skin-friction-coefficient expressions of Spalding and Chi and Van Driest are used in the solution of the momentum equation and in the heat-transfer predictions that use several modified forms of Reynolds analogy.

Boney, L. R.↗

NASA NTRS1974

Calculation method for active silencers with a variable section

By introducing variable section silencers in divergent and convergent sections or elbows of ventilation plants, the length of classical silencers can be reduced. Presented is an original calculation method for active noise silencers with a continuously variable section, as well as calculation relations worked out by this method for eight common practical cases.

Marinescu, V.↗

NASA NTRS1974

Exhaust-nozzle characterisitcs for a twin-jet variable-wing-sweep fighter airplane model at Mach numbers to 2.2

A wind-tunnel investigation has been conducted to determine the exhaust-nozzle aerodynamic and propulsive characteristics for a twin-jet variable-wing-sweep fighter airplane model. The powered model was tested in the Langley 16-foot transonic tunnel and in the Langley 4-foot supersonic pressure tunnel at Mach numbers to 2.2 and at angles of attack from about minus 2 to 6 deg. Compressed air was used to simulate the nozzle exhaust flow at values of jet total-pressure ratio from approximately 1 (jet off) to about 21. Effects of configuration variables such as speed-brake deflection, store installation, and boundary-layer thickness on the the nozzle characteristics were also investigated.

Reubush, D. E.↗

NASA NTRS1974

Variability of intensity ratios of H to He and He to ions with Z not smaller than 3 in solar energetic particle events

Data from the solid-state detector on Explorer 35 are applied to a study of two intensity ratios in the sub-MeV per nucleon specific kinetic energy range for several energetic particle events. It is found that the intensity ratios vary markedly from event to event, particularly during the time history of the individual events. This implies that the ratios have no simple relationship to 'solar abundances' in the usual sense of the term. The pattern of the variability of each ratio is established; the ratio of He to ions with Z not smaller than 3 starts with a low value and increases as the event proceeds. The H/He ratio exhibits a qualitatively similar time history with marked relative enhancement of He early in an event. Differential diffusion of the various ionic species with differing magnetic rigidities is seen to be the dominant physical cause for the variabilities observed.

Van Allen, J. A.↗

NASA NTRS1974

Infrared variability of V1016 Cygni

Infrared data obtained from broad-band photometric observations on the 60-inch telescope of the Hale observatories on Mount Wilson with the Becklin-Neugebauer photometer are discussed. The infrared magnitudes (shown as a function of time) illustrate the periodic nature of the V1016 Cygni variations. In particular, it can be seen that the longer-wavelength IR emission between 3 and 10 microns varies along with the shorter-wavelength emission. Although other explanations are possible, the infrared variability and luminosity of V1016 Cyg suggests the presence of Mira variable component together with the hot component now seen visually.

Harvey, P. M.↗

NASA NTRS1974

Optimal control problems with mixed control-phase variable equality and inequality constraints

In this paper, necessary conditions are obtained for optimal control problems containing equality constraints defined in terms of functions of the control and phase variables. The control system is assumed to be characterized by an ordinary differential equation, and more conventional constraints, including phase inequality constraints, are also assumed to be present. Because the first-mentioned equality constraint must be satisfied for all t (the independent variable of the differential equation) belonging to an arbitrary (prescribed) measurable set, this problem gives rise to infinite-dimensional equality constraints. To obtain the necessary conditions, which are in the form of a maximum principle, an implicit-function-type theorem in Banach spaces is derived.

Makowski, K.↗

NASA NTRS1974

The solution of three-variable duct-flow equations

This paper establishes a numerical method for the solution of three-variable problems and is applied here to rotational flows through ducts of various cross sections. An iterative scheme is developed, the main feature of which is the addition of a duplicate variable to the forward component of velocity. Two forward components of velocity result from integrating two sets of first order ordinary differential equations for the streamline curvatures, in intersecting directions across the duct. Two pseudo-continuity equations are introduced with source/sink terms, whose strengths are dependent on the difference between the forward components of velocity. When convergence is obtained, the two forward components of velocity are identical, the source/sink terms are zero, and the original equations are satisfied. A computer program solves the exact equations and boundary conditions numerically. The method is economical and compares successfully with experiments on bent ducts of circular and rectangular cross section where secondary flows are caused by gradients of total pressure upstream.

Stuart, A. R.↗

NASA NTRS1975

Ground idle performance improvement of a double-annular combustor by using simulated variable combustor geometry

A test program was undertaken to determine if variable combustor geometry could be used to reduce exhaust emissions of a low-pressure-ratio jet engine operating at ground idle conditions. Three techniques for varying combustor geometry were simulated. Other techniques evaluated were radial fuel staging and the use of preheated fuel. When simulated variable combustor geometry was employed with radial fuel staging, combustion efficiency at a fuel-air ratio of 0.01 was increased from 77 to 95 percent, and exhaust emissions of unburned hydrocarbons and carbon monoxide were significantly reduced.

Schultz, D. F.↗

NASA NTRS1975

Performance of an isolated two-dimensional variable-geometry wedge nozzle with translating shroud and collapsing wedge at speeds up to Mach 2.01

A wind-tunnel investigation was conducted to determine the aeropropulsion performance (thrust-minus-drag) of a single-engine, variable-geometry, two-dimensional (2-D) wedge nozzle with simulated translating-shroud and collapsing-wedge mechanisms. The investigation was conducted statically and at Mach numbers from 0.60 to 2.01 at an angle of attack of 0 deg and at varied jet total-pressure ratios up to 21, depending on the Mach number. The results indicate that the isolated aeropropulsion performance of a variable-geometry two-dimensional wedge nozzle is competitive with axisymmetric nozzles at transonic and supersonic speeds, but the isolated performance is slightly inferior for static take-off and low subsonic speeds. With the use of a simple tertiary-air ejector, the static take-off performance was increased.

Maiden, D. L.↗

NASA NTRS1975

The equations of motion of an artificial satellite in nonsingular variables

The equations of motion of an artificial satellite are given in nonsingular variables. Any term in the geopotential is considered as well as luni-solar perturbations up to an arbitrary power of r/r prime; r prime being the geocentric distance of the disturbing body. Resonances with tesseral harmonics and with the moon or sun are also considered. By neglecting the shadow effect, the disturbing function for solar radiation is also developed in nonsingular variables for the long periodic perturbations. Formulas are developed for implementation of the theory in actual computations.

Giacaglia, G. E. O.↗

NASA NTRS1974

Effect of crosslinking density on biaxial relaxation of SBR by using reduced variables

The use of reduced variables to account for the effect of crosslinking density in a styrene-butadiene rubber (SBR) system is demonstrated for general biaxial stress states. Recently published results from stress relaxation tests on five SBR vulcanizates crosslinked to different degrees by tetramethylthiuram disulfide were superposed by using the crosslinking density as a reduction variable. The equilibrium shear modulus calculated from the master relaxation curve at long reduced times was in satisfactory agreement with other results for SBR. The time-axis shifts were related in a linear logarithmic manner to the crosslinking density but had a slope slightly less than values previously reported for elastomer systems.

Arenz, R. J.↗