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At least 343 records · Page 19

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NASA NTRS1972

A method for integrating the boundary-layer equations through a region of reverse flow.

Development of a procedure for numerically integrating the boundary-layer equations through a region of reverse flow which takes downstream influence into account. This method is applied to the problem of uniform flow past a parallel flat plate of finite length whose surface has a constant velocity directed opposite to that of the main stream. Although singularities occur at both the point of detachment (x sub s) and reattachment (x sub r) of the psi = 0 streamline, this integration technique provides a solution which ceases to apply only in the close proximity of these singular points. From this solution it is evident that, throughout a large portion of the separated region, the flow is strongly affected by conditions near x sub r, thereby demonstrating the importance of allowing information to be transmitted upstream in a region of backflow. Near x sub s, however, it is found that, in spite of the presence of reverse flow, the solution has a self-similar form in this particular example.

Klemp, J. B.↗

NASA NTRS1972

The plasmapause as measured in positive ions.

Use of extensions of the existing theory of magnetospheric convection to describe the dynamics of the plasmasphere and the variation in the plasmapause location. The equatorial local time plane is divided into three separate and physically distinct regions, the bulge region, the nightside region, and the dayside region, corresponding to local times of 1500 to 2200 hrs, 2200 to 0600 hrs, and 0600 to 1500 hrs, respectively. The characteristics predicted by the model in the bulge region are: presence of the bulge at dusk, 1/R to the 4th power radial dependence of plasma concentration, and large fluctuations in plasma density at the plasmapause and plasma detachment. In the nightside region the predicted characteristics are: rapid response to magnetic activity changes, formative region for plasmasphere ripples, and the formative region for the dayside plasmapause location. The model also predicts the dayside plasmasphere characteristics, such as the slow response to magnetic activity changes, and filling of the plasmasphere from the ionosphere, including the formation of a 'double plasmapause.'

Sharp, G. W.↗

NASA NTRS1973

A method for predicting shock shapes and pressure distributions on two dimensional airfoils at large angles of attack

A method is presented for determining shock envelopes and pressure distributions for two-dimensional airfoils at angles of attack sufficiently large to cause shock detachment and subsonic flow over the windward surface of the airfoil. Correlation functions obtained from exact solutions are used to relate the shock standoff distance at the stagnation and sonic points of the body through a suitable choice for the shock shape. The necessary correlation functions were obtained from perfect gas solutions but may be extended to any gas flow for which the normal shock-density ratio can be specified.

Kaattari, G. E.↗

NASA NTRS1973

Self-recording portable soil penetrometer

A lightweight portable penetrometer for testing soil characteristics is described. The penetrometer is composed of a handle, data recording, and probe components detachably joined together. The data recording component has an easily removed recording drum which rotates according to the downward force applied on the handle, and a stylus means for marking the drum along its height according to the penetration depth of probe into the soil.

Costes, N. C.↗

NASA NTRS1973

Net vapor generation point in boiling flow of trichlorotrifluoroethane at high pressures

The conditions at which the void in subcooled boiling starts to undergo a rapid increase were studied experimentally. The experiments were performed in a 12.7 x 9.5 mm rectangular channel. Heating was from a 3.2 mm wide strip embedded in one wall. The pressure ranged from 9.45 to 20.7 bar, mass velocity from 600 to 7000 kg/sq m sec, and subcooling from 16 to 67 C. Photographs were used to determine when detached bubbles first appeared in the bulk flow. Measurements of bubble layer thickness along the wall were also made. Results showed that the point of net vapor generation is close to the occurrence of fully-developed boiling.

Dougall, R. S.↗

NASA NTRS1972

Users manual for Streamtube Curvature Analysis: Analytical method for predicting the pressure distribution about a nacelle at transonic speeds, volume 2

A special version of the Streamtube Curvature Analysis (STC) was been constructed to include a detached bow shock upstream of a plane or axisymmetric inlet. The bow wave is modeled using the method of Moeckel in conjunction with an approximate definition of the shock stand-off distance. A description of the Moeckel method and its implementation in the STC program are given.

Ferguson, D. R.↗

NASA NTRS1973

An experimental investigation of mesospheric ionization

Mesospheric ionization and its variability are examined. Data were obtained primarily by the parachute-borne blunt probe technique conducted in coordinated rocket experiments at White Sands Missile Range, New Mexico and Wallops Island, Virginia. Electrical conductivity measurements and deduced charge density values from ten rocket launches are presented and discussed. Positive ion conductivity and electron density were found to be relatively invariant with height between 45 and 60 km. Variations in positive conductivity of a factor of two and enhancements in negative conductivity by as much as a factor of four were measured by the blunt probe. A simple lumped parameter ion chemistry model is shown to satisfactorily explain the charge density values for the undisturbed lower D-region. Implications of the data in terms of this model are considered. The principal loss mechanism for positive ions in the 45 to 60 km. region is concluded to be dissociative recombination. Electron densities deduced from the conductivity data are explained by detachment involving a minor neutral constituent which is mixed between 65 and 45 km. and then cuts off sharply below 45 km. A correlation study involving blunt probe measurements shows relatively good agreement between variations in positive conductivity and temperature.

Mitchell, J. D.↗

NASA NTRS1972

Tidal evolution in close binary systems.

Mathematical outline of the theory of tidal evolution in close binary systems of secularly constant total momentum. Following a general outline of the problem the basic expressions for the energy and momenta of close binaries consisting of components of arbitrary internal structure are established, and the maximum and minimum values of the energy (kinetic and potential) which such systems can attain for a given amount of total momentum are investigated. These results are compared with the actual facts encountered in binaries with components whose internal structure (and, therefore, rotational momenta) are known from evidence furnished by the observed rates of apsidal advance. The results show that all such systems whether of detached or semidetached type - disclose that more than 99% of their total momenta are stored in the orbital momentum. The sum of the rotational momenta of the constituent components amounts to less than 1% of the total -a situation characteristic of a state close to the minimum energy for given total momentum.

Kopal, Z.↗

NASA NTRS1973

Analysis of embedded shock waves calculated by relaxation methods.

The requirements for uniqueness of the calculated jump conditions across embedded shock waves are investigated for type-dependent difference systems used in transonic flow studies. A mathematical analysis shows that sufficient conditions are (1) the equations should be differenced in conservative form and (2) a special difference operator should be used when switching from a hyperbolic to an elliptic operator. The latter results in a consistency condition on the integral equations, rather than the differential, at these points. Calculated jump conditions for several embedded and detached shock waves are analyzed in the physical and hodograph planes. Comparisons are made with previous results, a time-dependent calculation, and data.

Murman, E. M.↗

NASA NTRS1973

Pioneer spacecraft for atmospheric entry missions to the outer planets.

The composition of the atmospheres of the Jovian planets is probably representative of the composition of the original matter from which the solar system was formed. An entry probe would be required for obtaining quantitative data about the atmosphere as a function of altitude. A mission involving the detachment of an atmospheric entry probe from a Pioneer spacecraft is being considered. Instruments in the probe are to measure pressure, temperature, and composition of the atmosphere during descent. The Pioneer spacecraft is to serve as a communications relay for the data transmitted from the probe.

Dixon, W. J.↗

NASA NTRS1973

The role of rotation in close binary systems of high mass.

A quantitative confrontation of theory and observation of massive close binary systems is presented in order to evaluate the role of axial rotation in the evolution of the individual stellar components as well as of the system as a whole. The detached systems are essentially unevolved, and possess components in approximately uniform rotation. The semidetached systems are definitely evolved, having suffered a heavy mass exchange before the stage of hydrogen exhaustion at the center of the original primary, and often possess mass-gaining components in fast nonuniform rotation. Except in the case of wide systems, tidal friction eventually reinduces synchronism of rotation in both components and both components evolve inhomogeneously. Spin-down times of the envelope and core, total rotational angular momenta, and effects of spin-orbit interaction are calculated.

Stothers, R.↗

NASA NTRS1974

A compilation and analysis of typical approach and landing data for a simulator study of an externally blown flap STOL aircraft

A piloted simulation study has been made of typical landing approaches with an externally blown flap STOL aircraft to ascertain a realistic dispersion of parameter values at both the flare window and touchdown. The study was performed on a fixed-base simulator using standard cockpit instrumentation. Six levels of stability and control augmentation were tested during a total of 60 approaches (10 at each level). A detached supplement containing computer printouts of the flare-window and touchdown conditions for all 60 runs has been prepared.

Middleton, D. B.↗

NASA NTRS1974

Orbital and entry tracking accessory for globes

An orbital and entry tracking accessory or attachment is described which can be mounted on a globe to provide a rapid means of determining range requirements for entry vehicles returning from any orbit to any desired landing site with reasonable accuracy. The device is constructed of clear plastic strip material, and comprises a support ring, a calibrated orbital track member rigidly carried by the support ring, and a calibrated lateral range member pivotally coupled to the support ring at points such that the lateral range member is always oriented normally to the orbital track member. The assembly is mountable on the globe relatively snugly, but freely movable. At least one of the members has a detachable coupling which permits placement of the device on the globe.

Pritchard, E. B.↗

NASA NTRS1974

Removal of spacecraft-surface particulate contaminants by simulated micrometeoroid impacts

A series of hypervelocity impacts has been conducted in an exploding lithium-wire accelerator to examine with a far-field holographic system the removal of particulate contaminants from external spacecraft surfaces subjected to micrometeoroid bombardment. The impacting projectiles used to simulate the micrometeoroids were glass spheres nominally 37 microns in diameter, having velocities between 4 and 17 km/sec. The particulates were glass spheres nominally 25, 50, and 75 microns in diameter which were placed on aluminum targets. For these test, particulates detached had velocities that were log-normally distributed. The significance of the log-normal behavior of the ejected-particulate velocity distribution is that the geometric mean velocity and the geometric standard deviation are the only two parameters needed to model completely the process of particles removed or ejected from a spacecraft surface by a micrometeoroid impact.

Goad, J. H., Jr.↗

NASA NTRS1974

Pioneer 10 observations of the solar wind interation with Jupiter

Pioneer 10 Plasma Analyzer experiment flight data during the Jupiter flyby are presented. The observations show that the interaction of Jupiter's magnetic field with the solar wind is similar in many ways to that at earth, but the scale size is over 100 times larger. Jupiter is found to have a detached standing bow shock wave of high Alfven Mach number. Jupiter has a prominent magnetopause which deflects the magnetosheath plasma and excludes its direct entry into the Jovian magnetosphere. The sunward hemisphere of Jupiter's outer magnetosphere is found to be highly inflated with thermal plasma and a high beta region which is highly responsive to changes in solar wind dynamic pressure. Observational arguments are presented which tend to discount a thin disklike magnetosphere but, rather, favor a Jovian magnetosphere, albeit probabily considerably flattened as compared to the earth's magnetosphere, yet still with reasonable thickness. Results concerning the shock jump conditions, the magnetosheath flow field and inferred internal magnetospheric plasma are presented.

Wolfe, J. H.↗

NASA NTRS1974

Isolated cold plasma regions: Observations and their relation to possible production mechanisms

Regions of enhanced cold plasma, isolated from the main plasmasphere along the Explorer 45 orbit on the equatorial plane, are reported using the sheath induced potentials seen by the electric field experiment. The occurrence of these regions has a strong correlation with negative enhancements of Dst, and their locations are primarily in the noon-dusk quadrant. The data support the concept that changes in large scale convection play a dominant role in the formation of these regions. Plasmatails that are predicted from enhancements of large scale convection electric fields in general define where these regions may be found. More localized processes are necessary to account for the exact configuration and structure seen in these regions and may eventually result in detachment from the main plasmasphere.

Maynard, N. C.↗

NASA NTRS1974

Magnetic field observations near Mercury: Preliminary results from Mariner 10

Results are presented from a preliminary analysis of data obtained near Mercury by the NASA/GSFC Magnetic Field Experiment on Mariner 10. A very well developed, detached bow shock wave, which developed as the super-Alfvenic solar wind interacted with the planet Mercury was observed. A magnetosphere-like region, with maximum field strength of 98 gamma at closest approach (704 km altitude) was also observed, and was contained within boundaries similar to the terrestrial magnetopause. The obstacle deflecting the solar wind flow was global in size, but the origin of the enhanced magnetic field was not established. The most plausible explanation, considering the complete body of data, favored the conclusion that Mercury has an intrinsic magnetic field.

Ness, N. F.↗

NASA NTRS1973

Characterizations of four specimens processed as a part of the M553 sphere forming experiment performed during the Skylab 1 and 2 flight

Four specimens identified as SL-1.3, SL-1.8, SL-1.9 and SL-2.5 were submitted for metallurgical characterization. These specimens had been processed in the M512 Facility as a part of the M553 Sphere Forming Experiment performed during the Skylab 1/2 flight. Three of these specimens, SL-1.3, SL-1.8, and SL-2.5 were designed to be melted completely by the electron beam and detach themselves from their support posts and resolidify while floating free in the near zero gravity and vacuum environment of space. Specimens SL-1.3 and SL-1.8 were completely melted, but it is believed they did not leave their posts before solidifying. Specimen SL-2.5 was only partially melted. Specimen SL-1.9 was to be completely melted and retained on a large sting which was accomplished as planned. The nominal composition of the four specimens was: (1) SL-1.3 - Ni 12% Sn; (2) SL-1.8 - Ni 30% Cu; (3) SL-1.9 - Pure Ni; and (4) SL-2.5 - Pure Ni. These four specimens have been examined according to the Phase B Characterization Plan. The results are discussed and compared with similar characterization analyses run on ground base specimens.

Hubbard, J. L.↗