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At least 1,027 records · Page 57

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NASA NTRS1984

Error determination of a successive correction type objective analysis scheme

The Purdue Regional Objective Analysis of the Mesoscale (PROAM) is a successive correction type scheme for the analysis of surface meteorological data. The scheme is subjected to a series of experiments to evaluate its performance under a variety of analysis conditions. The tests include use of a known analytic temperature distribution to quantify error bounds for the scheme. Similar experiments were conducted using actual atmospheric data. Results indicate that the multiple pass technique increases the accuracy of the analysis. Furthermore, the tests suggest appropriate values for the analysis parameters in resolving disturbances for the data set used in this investigation.

Smith, D. R.↗

NASA NTRS1984

Heating the sun's lower transition region with fine-scale electric currents

Analytical and observational data are presented to show that the lower transition zone, a 100 km thick region at 10,000-200,000 K between the solar chromosphere and corona, is heated by local electric currents. The study was spurred by correlations between the enhanced atmospheric heating and magnetospheric flux in the chromospheric network and active regions. Field aligned current heated flux loops are asserted to mainly reside in and make up most of the transition region. It is shown that thermal conduction from the sides of hot gas columns generated by the current dissipation is the source of the observed temperature distribution in the transition regions.

Rabin, D.↗

NASA NTRS1984

Morphological stability in the presence of fluid flow in the melt

Recent experiments have shown that the presence of a vertical buoyancy-driven flow adjacent to an initially cylindrical crystal-melt interface may produce a time-dependent helical deformation of the interface, with a rotation period ranging from several minutes to many hours, depending upon the width of the melt. The temperature distribution is such that the interface is expected to be morphologically stable in the absence of fluid flow. A linear stability analysis reveals that the instability is due to a coupling between a basic hydrodynamic instability in the buoyant flow and the deformable boundary separating the two phases. The crystal-melt interface lowers the critical Grashof number of an analogous rigid-walled system by an order of magnitude for succinonitrile with a Prandtl number P = 22.8; furthermore, the hydrodynamic mode that is actually destabilized by the interface is not the least stable mode in the rigid-walled system for P = 22.8. The results show that the instability may be regarded either as a rather large alteration of a basic hydrodynamic instability by the crystal-melt interface, or as a significant modification of the morphological stability of the interface by the presence of the buoyant flow.

Mcfadden, G. B.↗

NASA NTRS1984

Fast numerical calculations of EHD sliding traction forces Application to rolling bearings

Based on analytical calculations assuming isothermal elastohydrodynamic (EHD) lubrication conditions, and on curve-fitting of a thermal correction factor, a new formula is proposed to calculate the sliding traction force developed in a concentrated contact, assuming a nonlinear, viscoelastic lubricant and undirectional sliding. When sliding occurs in the rolling and transverse directions (bidimensional sliding), a simplified numerical method is outlined by which the components of the local shear stress are quickly calculated. The latter method is applied to the calculation of the shear stress and temperature distribution in the ball-raceway contacts of an angular-contact ball bearing. Because of the viscoelastic behavior of the lubricant, a nonzero lateral traction force is obtained.

Houpert, L.↗

NASA NTRS1985

Effect of variable surface catalysis on heating near the stagnation point of a blunt body

This paper describes arc-jet data obtained on the performance of glass coated thermal protection systems in a convectively heated environment. These data confirm earlier flight and arc-jet data that show an increased surface catalysis with salt contamination and a decreased surface catalysis near the softening point temperature of the glass. In addition, surface temperature distributions along sphere-cones with abruptly changing surface catalysis were measured near the stagnation point and compared well with computations using a reacting boundary layer code.

Stewart, D. A.↗

NASA NTRS1985

Dynamic characteristics of statically determinate space-truss platforms

The geometry of a class of statically determinate platforms is developed and vibration frequencies determined. Such configurations would allow shape control by changing member lengths to be accomplished with small forces. An additional advantage of a statically determinate structure is being free of thermal stress under any temperature distribution. Frequency comparisons between statically determinate and more conventional redundant platforms are presented. Vibration of curved platforms that could be used as antenna concepts is also investigated. Alternate concepts incorporating the statically determinate design but having improved dynamic characteristics are suggested.

Anderson, M. S.↗

NASA NTRS1984

Application of viscous and inviscid computation methods for rocket turbopump systems

This paper examines current research efforts underway at Lewis Research Center which have focused on improving the structural durability of the SSME turbodrive system through more fully examining the aerothermodynamics of the flow system. This objective was achieved by developing three-dimensional viscous and inviscid computer codes to predict the pressure and temperature distributions in the engine flow passages, particularly within the SSME turbines and turnaround ducts.

Povinelli, L. A.↗

NASA NTRS1985

Effects of rotation on impingement cooling of turbine blades

The effects of rotation on impingement cooling of turbine blades were studied experimentally as a specialized facility at M.I.T. A foil heated resistively was cooled by a jet flow on one side and temperature monitored on the other. Rotating the blade limits the heat transfer path to conduction through the support structure and radiation. IR radiometry furnishes the temperature distributions on the chamber wall, permitting the internal heat transfer coefficient to be measured. The heat transfer efficiency has been found to fall as much as 30 percent as rotational speed increases. The conditions observed confirm the significance of rotational effects, particularly with regard to potential early blade failure.

Kreatsoulas, J. C.↗

NASA NTRS1985

Heat generation in aircraft tires

A method was developed for calculating the internal temperature distribution in an aircraft tire while free rolling under load. The method uses an approximate stress analysis of each point in the tire as it rolls through the contact patch, and from this stress change the mechanical work done on each volume element may be obtained and converted into a heat release rate through a knowledge of material characteristics. The tire cross-section is then considered as a body with internal heat generation, and the diffusion equation is solved numerically with appropriate boundary conditions of the wheel and runway surface. Comparison with data obtained with buried thermocouples in tires shows good agreement.

Clark, S. K.↗

NASA NTRS1985

Gravity Waves

In recent years it has been widely recognized that vertically propagating gravity waves play an important role in the dynamics of the middle atmosphere in partly determining the large scale temperature and wind structure through their energy and momentum transport. In particular, the meridional temperature distribution and the mean wind profile in the upper mesosphere are considered to be largely affected by the turbulence diffusion and friction that gravity waves induce through their breaking. For an understanding of the middle atmosphere circulation, it is therefore very important to know the global distribution and temporal variation of gravity waves in a climatological sense. The results of the statistics for gravity wave activity in the stratosphere and mesosphere are presented as a function of latitude and month, with the aid of meteorological rocket network observations.

Hirota, I.↗

NASA NTRS1985

A Proposed International Tropical Reference Atmosphere up to 80 Km

Based upon previous standard reference atmosphere, which are usually inspired by temperature regions, a proposal is made for an International Tropical Reference Atmosphere (ITRA). It is a modification of the Indian Standard Tropical Atmosphere (ISIA). The data at the available longitudinal stations in the tropics was considered in formulating the present proposal. Balloonsonde, rocketsonde, and grenade and falling sphere data was used in developing the temperature data bse fromt he stratosphere, troposphere and mesosphere. Temperature distribution and mean sea level pressures up to 80 km altitudes is discussed.

Ananthasayanam, M. R.↗

NASA NTRS1985

Analysis and interpretation of MAGSAT anomalies over north Africa

Crustal anomaly detection with MAGSAT data is frustrated by inherent resolving power of the data and by contamination from external and core fields. Quality of the data might be tested by modeling specific tectonic features which produce anomalies that fall within proposed resolution and crustal amplitude capabilities of MAGSAT fields. To test this hypothesis, north African hotspots associated with Ahaggar, Tibesti and Darfur were modeled as magnetic induction anomalies. MAGSAT data were reduced by subtracting external and core fields to isolate scalar and vertical component crustal signals. Of the three volcanic areas, only the Ahaggar region had an associated anomaly of magnitude above error limits of the data. Hotspot hypothesis was tested for Ahaggar by seeing if predicted magnetic signal matched MAGSAT anomaly. Predicted model magnetic signal arising from surface topography of the uplift and the Curie isothermal surface was calculated at MAGSAT altitudes by Fourier transform technique modified to allow for variable magnetization. Curie isotherm surface was calculated using a method for temperature distribution in a moving plate above a fixed hotspot. Magnetic signal was calculated for a fixed plate as well as a number of plate velocities and directions.

Phillips, R. J.↗

NASA NTRS1985

Dilution jet mixing program, phase 3

The main objectives for the NASA Jet Mixing Phase 3 program were: extension of the data base on the mixing of single sided rows of jets in a confined cross flow to discrete slots, including streamlined, bluff, and angled injections; quantification of the effects of geometrical and flow parameters on penetration and mixing of multiple rows of jets into a confined flow; investigation of in-line, staggered, and dissimilar hole configurations; and development of empirical correlations for predicting temperature distributions for discrete slots and multiple rows of dilution holes.

Srinivasan, R.↗

NASA NTRS1986

Nucleation experiments in a microgravity environment

A simple experimental apparatus is described in which a wide variety of vapor phase nucleation studies of refractory materials could be performed aboard NASA's KC-135 Research Aircraft. The chief advantage of a microgravity environment for these studies is the expected absence of thermally driven convective motions in the gas. The absence of convection leads to much more accurate knowledge of both the temperature distribution in the system and the time evolution of the refractory vapor concentration as a function of distance from the crucible.The evolution of the apparatus will be described as more experience is gained with the microgravity environment. Such experiments will be used to prepare for similar ones carried out aboard either the shuttle or Space Station where considerably longer duration experiments are possible.

Nuth, J. A.↗

NASA NTRS1986

Development of an Emulation-simulation Thermal Control Model for Space Station Application

Analysis techniques to evaluate the effects of changing thermal loads and the methods utilized to control temperature distributions in the orbital space station are essential. Analysis techniques including a user-friendly computer program, were developed which should prove useful in thermal design and system analysis of the the space station. The program uses a data base and user input to compute costs, sizes, and power requirements for individual components and complete systems. User input consists of selecting mission parameters, selecting thermal acquisition configurations, transport systems and distances, and thermal rejection configurations.

Colwell, G. T.↗

NASA NTRS1985

The effects of strain heating in lithospheric stretching models

The deformation by stretching of a continental type lithosphere has been formulated so that the problem can be solved by a continuum mechanical approach. The deformation, stress state, and temperature distribution are constrained to satisfy the physical laws of conservation of mass, energy, momentum, and an experimentally defined rheological response. The conservation of energy equation including a term of strain energy dissipation is given. The continental lithosphere is assumed to have the rheology of an isotropic, incompressible, nonlinear viscous, two layered solid.

Stanton, M.↗

NASA NTRS1986

Wall layer models for the calculation of velocity and heat transfer in turbulent boundary layers

In the computation of turbulent boundary-layer flows and internal flows, a substantial amount of mesh points and computational effort is required to adequately resolve the intense temperature and velocity profile variations in the near wall region. In this study, analytical profile approximations are obtained for the mean velocity and temperature distribution in the wall layer; these profiles are based upon consideration of the observed coherent structure of the time-dependent wall-layer flow. The profile approximations are relatively simple analytical formulae which satisfy all the required compatibility conditions at the wall and the logarithmic behavior at the edge of the wall layer. The Reynolds analogy for heat transfer is not used in the present theory. A general method for utilizing the present wall-layer profile models in a prediction method is indicated.

Walker, J. D. A.↗

NASA NTRS1986

Liquid droplet radiator thermal characteristics

The effects of droplet size, emissivity, and spacing on the liquid droplet radiator (LDR) performance space heat rejection system are investigated. The procedures for predicting surface emissivity of semitransparent droplets as a function of absorptivity and radius are examined. The relation between absorptivity, reflectivity, transmissivity, and emissivity is studied. It is observed that for droplets in the 25-200 micron range the radius affects emissivity. The thermal performance of an array of droplet streams is described using a thermal radiation model. Droplet temperatures are calculated; it is shown that outside droplet streams are more effective than interior droplets for arrays in the range of radius to spacing ratio from 0.05-0.2. Temperature distributions as a function of droplet size, emissivity, and velocity are presented. The heat transfer performance of a LDR is evaluated in terms of fin effectiveness. The equivalent sheet emissivities of droplet streams are examined.

Edgerton, R. H.↗