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At least 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Three dimensional compressible boundary-layer computations for a finite swept wing

Three-dimensional, compressible turbulent boundary-layer calculations have been performed for the finite supercritical wing of the NASA modified F8 transonic research airplane. Data on the boundary-layer thickness, displacement thickness, skin friction components, and integrated streamwise skin friction are presented for points along the streamwise stations of which the pressure measurements were previously made. Representative velocity profiles are shown, and boundary-layer-thickness contour plots and skin-friction vector plots are presented. Results are given for a Reynolds number of 1.5 million per foot, and for Mach numbers of 0.50 and 0.99.

Nash, J. F.↗
NASA NTRS1971

A graphite/epoxy compression panel for the space shuttle.

Martin Marietta fabricated a hat-section-stiffened compression panel of graphite/epoxy composite that was analyzed to optimize the structural configuration and material distribution. The fabrication processes developed were modified following the appearance of several problems associated with the unique physical properties of the material. Quality control processes were developed, with emphasis in the areas of ultrasonics and X-ray.

Meredith, O. D.↗
NASA NTRS1971

Effects of compression and random noise on multispectral data.

Two problem areas are often encountered in the use of multispectral scanner data: (1) large quantities of man and machine time are required to analyze and store the volumes of data gathered and (2) the quality of the data is usually reduced by the introduction of unwanted random noise. This paper will present some effects of data compression and random noise on multispectral data, particularly as they apply to pattern recognition and picture quality.

Ready, P. J.↗
NASA NTRS1971

Waves along a cylindrical 'grid-like' antenna in an anisotropic compressible plasma.

The dispersion equation is obtained analytically of waves along an infinitely long cylindrical ?grid-like' antenna in an anisotropic compressible homogeneous plasma. Numerical solutions of this equation show that an external static magnetic field has great influence upon the anomalously dispersive region of the dispersion relation around the plasma frequency.

Yu, W.↗
NASA NTRS1971

A numerical investigation into the effects of compressibility and total enthalpy difference on the development of a laminar free shear layer.

A method is presented for integrating numerically the equations of motion for a compressible free shear layer developing from a boundary-layer profile of arbitrary shape. Sutherland's law is used to determine the coefficient of viscosity and the Prandtl number is taken as 0.72. Calculated results are reported for free-stream Mach numbers ranging from 0 to 10 and for stagnation-enthalpy ratios ranging from 0 to 5.0. The effects of varying the initial boundary-layer profile and of a discontinuity in temperature at the origin are also studied. The results include graphs showing the development of dividing-streamline velocity, of local Nusselt number, and of dividing-streamline location.

Carpenter, P. W.↗
NASA NTRS1971

Adaptive variable-length coding for efficient compression of spacecraft television data.

An adaptive variable length coding system is presented. Although developed primarily for the proposed Grand Tour missions, many features of this system clearly indicate a much wider applicability. Using sample to sample prediction, the coding system produces output rates within 0.25 bit/picture element (pixel) of the one-dimensional difference entropy for entropy values ranging from 0 to 8 bit/pixel. This is accomplished without the necessity of storing any code words. Performance improvements of 0.5 bit/pixel can be simply achieved by utilizing previous line correlation. A Basic Compressor, using concatenated codes, adapts to rapid changes in source statistics by automatically selecting one of three codes to use for each block of 21 pixels. The system adapts to less frequent, but more dramatic, changes in source statistics by adjusting the mode in which the Basic Compressor operates on a line-to-line basis. Furthermore, the compression system is independent of the quantization requirements of the pulse-code modulation system.

Rice, R. F.↗
NASA NTRS1971

Facsimile bandwidth compression using nonlinear analog processing.

A system is presented for reducing the number of picture elements in a scanned image by an order of magnitude while preserving the detail contrast. Starting with high-resolution data a 3 x 3 matrix of input elements is compressed into a single output element using a nonlinear algorithm. Optimum results are obtained by including the data on the outer periphery of the input sample in the processing algorithm thus requiring a 5 x 5 input matrix. Experimental results are presented using weather satellite photographs. This system has application in those cases where the sensor has higher resolution capability than the communication link can support.

Macovski, A.↗
NASA NTRS1972

Compressive strength of titanium alloy skin-stringer panels selectively reinforced with boron-aluminum composite.

Description of a method of selectively reinforcing conventional titanium airframe structure with unidirectional boron-aluminum composite attached by brazing which has been successfully demonstrated based on compression tests of short skin-stringer panels. Improvements in structural performance exceeded 25% on an equivalent weight basis over the range from room temperature to 800 F, both in terms of initial buckling and maximum strengths. Room-temperature performance was not affected by prior exposure at 600 F for 1000 hours in air, or by 400 cycles between -65 and 600 F. The experimental results were generally predictable on the basis of existing analytical procedures. No evidence of failure was observed in the braze bond between the boron-aluminum composite and the titanium alloy.

Herring, H. W.↗
NASA NTRS1972

Measurement of apparent thermal conductivity of multilayer insulations at low compressive loads.

A description is presented of the test calorimeter, the experimental technique, and the results obtained in an evaluation of four multilayer insulations selected for application on future multilaunch space vehicles utilizing liquid hydrogen and oxygen for orbital operations. Particular attention is paid to techniques for minimizing error in obtaining thermal conductivity data. The effective conductivity for four high-performance insulations was determined at a minimum of four compressive loads in the range from 0.0001 to 0.1 psi. Results show that the thermal conductivity of multilayer insulations is insensitive to small changes in mechanical loading at 1 torr interstitial gas pressure, but becomes increasingly more sensitive to mechanical loading as the interstitial gas pressure is reduced.

Holmes, V. L.↗
NASA NTRS1972

Dielectric constant of compressed gaseous and liquid oxygen.

The dielectric constants of compressed gaseous and liquid oxygen were measured on ten isoterms at temperatures between 100 and 300 K and on the saturated liquid boundary at temperatures between 55 and 154 K. Densities ranged from 0.06 to 1.30 grams per cu cm at pressures up to 33 MN per sq m. The dielectric constant measurements were combined with accurate density data to compute the Clausius-Mossotti function. This function was found to decrease for oxygen with density from a value of 0.1236 cu cm per gram at the low density limit to 0.1219 cu cm per gram near the triple point.

Younglove, B. A.↗
NASA NTRS1971

Possible flow regimes of adiabatic one-dimensional compressible fluid flow with friction in convergent and divergent ducts.

An analytical solution for the compressible one-dimensional flow in convergent and divergent ducts with friction is obtained. It is found that a nondimensional parameter, N, can be formed using the friction factor, duct half-angle and the ratio of specific heats of the gas. Seven flow regimes are describable with the solution, based on certain bounds on the magnitude of N. The regimes are discussed and corollary data are presented graphically.

Shouman, A. R.↗
NASA NTRS1972

A study of compressed spatially non-Gaussian optical pulses from mode-locked lasers.

The effect of the grating-induced phase and spatial modulations by multiple transverse modes simultaneously present in mode-locked laser pulses is investigated. Our analysis shows that the dispersions of the grating pair become strongly dependent on wavelength because of the energy exchanges occurring among transverse modes. As a result, the maximum-intensity trace at the output of the grating is shown to be curved and the grating-induced pulse-compression rate is shown to vary significantly across the beam cross section. Also, a discussion is presented relating our analysis to existing experimental data on the wavelength-dependent chirping rates of mode-locked laser beams.

Kim, D. M.↗
NASA NTRS1972

Buckling of circular cylindrical shells under axial compression.

The infinitely long cylindrical shell under axial compression with axisymmetric sinusoidal imperfections is considered. The bifurcation problem is formulated exactly, and a complete family of buckling modes is identified. Koiter's (1963) upper bound pertains to the critical stress associated with one restricted set of modes, and the critical stress for a set of long wavelength modes reproduces some numerical results obtained by Almroth (1966). The initial postbuckling analysis is also formulated exactly. An exact analytical solution is obtained for the limiting case of modes with infinitely long wavelengths, and numerical analysis is used to solve the equations for the other cases. An appendix gives the details of the analysis.

Budiansky, B.↗
NASA NTRS1973

Computer program for compressible flow network analysis

Program solves problem of an arbitrarily connected one dimensional compressible flow network with pumping in the channels and momentum balancing at flow junctions. Program includes pressure drop calculations for impingement flow and flow through pin fin arrangements, as currently found in many air cooled turbine bucket and vane cooling configurations.

Wilton, M. E.↗
NASA NTRS1973

Computer program for predicting symmetric jet mixing of compressible flow in jets

Finite-difference computer program has been developed for treating mixing of two parallel and compressible air streams; one of them may be supersonic. This development is restricted to symmetric jet mixing in which high-speed jet is located on axis of channel and no provision is made for blowing or suction along channel walls.

Gilbert, G. B.↗
NASA NTRS1972

A method for calculating laminar viscous, compressible flows with small pressure gradients

A method is presented for calculating laminar viscous, compressible flows in which pressure gradients are assumed to be neglibible in energy conservation and in developing property relations, but not in momentum conservation. The equations are developed from Navier-Stokes equations in a noninertial reference frame. The method is an extension of an approximate method developed for calculating combined forced and contained natural convection in a rotating tank. The restriction to small density and temperature variations in the previous method is removed. For illustration, a two-dimensional simulation of the rotating tank problem is formulated, and the numerical computation procedure to be used is indicated.

Martin, E. D.↗
NASA NTRS1972

Tests of a mixed compression axisymmetric inlet with large transonic mass flow at Mach numbers 0.6 to 2.65

A 38.8-cm (15.28-in.) capture diameter model of a mixed-compression axisymmetric inlet system with a translating cowl was designed and tested. The internal contours, designed for Mach number 2.65, provided a throat area of 59 percent of the capture area when the cowl was retracted for transonic operation. Other model features included a boundary-layer removal system, vortex generators, an engine airflow bypass system, cowl support struts, and rotating rakes at the engine face. All tunnel testing was conducted at a tunnel total pressure of about 1 atm (a unit Reynolds number of about 8.53 million/m at Mach number 2.65) at angles of attack from 0 deg to 4 deg. Results for the following were obtained: total-pressure recovery and distortion at the engine face as a function of bleed mass-flow ratio, the effect of bleed and vortex generator configurations on pressure recovery and distortion, inlet tolerance to unstart due to changes in angle of attack or Mach number, surface pressure distributions, boundary-layer profiles, and transonic additive drag. At Mach number 2.65 and with the best bleed configurations, maximum total pressure recovery at the engine face ranged from 91 to 94.5 percent with bleed mass-flow ratios from 4 to 9 percent, respectively, and total-pressure distortion was less than 10 percent. At off-design supersonic Mach numbers above 1.70, maximum total-pressure recoveries and corresponding bleed mass flows were about the same as at Mach number 2.65, with about 10 to 15 percent distortion. In the transonic Mach number range, total pressure recovery was high (above 96 percent) and distortion was low (less than 15 percent) only when the inlet mass-flow ration was reduced 0.02 to 0.06 from the maximum theoretical value (0.590 at Mach number 1.0).

Smeltzer, D. B.↗