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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Shear strength of lunar soil from Oceanus Procellarum.

Soil from the scoop of Surveyor 3, returned to earth by Apollo 12 astronauts, has been tested in a miniature shear box at five bulk densities, from 0.99 to 1.87 g/cu cm. Cohesion increased with bulk density from .03 to .3 N/sq cm; internal friction angle increased from 13 to 56 deg. Shear stress vs normal stress data fit a logarithmic relationship better than a linear one, at normal stresses of .003 to 3 N/sq cm. Results of these tests, in air, show no systematic differences from those for tests made elsewhere in vacuum and nitrogen. Results agree with those obtained in remotely controlled lunar surface operations with Surveyor 3 and other spacecraft provided that the bulk density was slightly underestimated for the on-surface measurements.

Jaffe, L. D.↗
NASA NTRS1977

Atmospheric model development in support of SEASAT. Volume 4: Forecast model sensitivity study

Atmospheric analysis and prediction models of varying (grid) resolution were developed. The models were tested using real observational data for the purpose of assessing the impact of grid resolution on short range numerical weather prediction. The work statement was amended to include the performance of sensitivity tests using a coarse mesh (63 x 63 x 5 level) prediction model in order to identify and order factors which might mask or impair the utility of SEASAT data on short range weather prediction. Such factors included: initial conditions; topography; surface friction; latent heating; diffusion of momentum and temperature; and computational devices such as tendency truncators, pressure smoothers, and temporal filters.

Lewit, H. L.↗
NASA NTRS1986

Turbulent boundary-layer wall pressure fluctuations downstream of a tandem LEBU

An initial measurement of turbulent wall pressure fluctuations downstream of tandem large eddy breakup devices (LEBUs) indicates a significant reduction by comparison with the reference case of a flat plate; the average magnitude of the reduction is 12.5 percent. Peak reduction is at 7-8 kHz, and is of the order of the C(f) reduction due to the tandem LEBUs. These data indicate a secondary benefit derivable from LEBUs, in addition to their skin friction reduction effect.

Beeler, G. B.↗
NASA NTRS1994

A comparison of turbulence models in computing multi-element airfoil flows

Four different turbulence models are used to compute the flow over a three-element airfoil configuration. These models are the one-equation Baldwin-Barth model, the one-equation Spalart-Allmaras model, a two-equation k-omega model, and a new one-equation Durbin-Mansour model. The flow is computed using the INS2D two-dimensional incompressible Navier-Stokes solver. An overset Chimera grid approach is utilized. Grid resolution tests are presented, and manual solution-adaptation of the grid was performed. The performance of each of the models is evaluated for test cases involving different angles-of-attack, Reynolds numbers, and flap riggings. The resulting surface pressure coefficients, skin friction, velocity profiles, and lift, drag, and moment coefficients are compared with experimental data. The models produce very similar results in most cases. Excellent agreement between computational and experimental surface pressures was observed, but only moderately good agreement was seen in the velocity profile data. In general, the difference between the predictions of the different models was less than the difference between the computational and experimental data.

Rogers, Stuart E.↗
NASA NTRS1942

The Performance of a Vaneless Diffuser Fan

The present paper is devoted to the theoretical and experimental investigation of one of the stationary elements of a fan, namely, the vaneless diffuser. The method of computation is based on the principles developed by Pfleiderer (Forschungsarbeiten No. 295). The practical interest of this investigation arises from the fact that the design of the fan guide elements - vaneless diffusers, guide vanes, spiral casing - is far behind the design of the impeller as regards accuracy and. reliability. The computations conducted by the method here presented have shown sufficiently good agreement with the experimental data and indicate the limits within which the values of the coefficient of friction lie.

Polikovsky, V.↗
NASA NTRS2004

NASA Tech Briefs, December 2004

opics include: High-Rate Digital Receiver Board; Signal Design for Improved Ranging Among Multiple Transceivers; Automated Analysis, Classification, and Display of Waveforms; Fast-Acquisition/Weak-Signal-Tracking GPS Receiver for HEO; Format for Interchange and Display of 3D Terrain Data; Program Analyzes Radar Altimeter Data; Indoor Navigation using Direction Sensor and Beacons; Software Assists in Responding to Anomalous Conditions; Software for Autonomous Spacecraft Maneuvers; WinPlot; Software for Automated Testing of Mission-Control Displays; Nanocarpets for Trapping Microscopic Particles; Precious-Metal Salt Coatings for Detecting Hydrazines; Amplifying Electrochemical Indicators; Better End-Cap Processing for Oxidation-Resistant Polyimides; Carbon-Fiber Brush Heat Exchangers; Solar-Powered Airplane with Cameras and WLAN; A Resonator for Low-Threshold Frequency Conversion; Masked Proportional Routing; Algorithm Determines Wind Speed and Direction from Venturi-Sensor Data; Feature-Identification and Data-Compression Software; Alternative Attitude Commanding and Control for Precise Spacecraft Landing; Inspecting Friction Stir Welding using Electromagnetic Probes; and Helicity in Supercritical O2/H2 and C7H16/N2 Mixing Layers.

Source record↗
NASA NTRS2025

Direct Numerical Simulation of Flow Past a Gaussian Bump at a High Reynolds Number

We present the results from a direct numerical simulation of a spanwise-periodic turbulent flow past a Gaussian bump. The problem setup is designed to investigate the interaction of an incoming turbulent boundary layer with the strong favorable and adverse pressure gradients generated by the Gaussian bump as the flow passes over it at a Reynolds number of 340000 based on the bump height, or 4 million based on the bump length. The statistical results from the present simulation are compared against our earlier results at a Reynolds number of 2 million. An internal layer, which forms beneath the strongly accelerated boundary layer over the windward side of the bump, is found to generate its near-wall turbulence stress peaks in closer proximity of the wall in the higher Reynolds-number case. Furthermore, the logarithmic layer of the higher Reynolds-number boundary layer appears more resistant to changes induced by strong acceleration and surface curvature effects over the same region. Despite a nearly identical flow separation point in the two flows, the detached shear layer grows at a faster rate and subsequently reattaches at an earlier point in the higher Reynolds-number flow. The surface pressure and skin-friction distributions over the attached flow region compare well against the corresponding experimental data for both flows. However, some differences appear in the separated flow region, which are attributed to the three-dimensionality of the experimental model setup that is not included in the simulation owing to the spanwise periodic assumption. Comparisons with the stereoscopic particle image velocimetry measurements on the central plane of the experimental model over the windward side of the bump show reasonable overall agreement in the mean velocity components, but the turbulence stress components do not agree well at some streamwise locations. Comparisons over the leeward side of the bump show that the mean separated shear layer in the simulation is tilted significantly more toward the wall than the experimental shear layer on the central plane. This mismatch in the mean shear layer orientation is due to the experimental model three-dimensionality and tunnel end-wall effects, which are not modeled in the present spanwise-periodic simulation.

Favorable and Adverse Pressure Gradients↗
NASA NTRS1987

Preliminary investigation of inertia friction welding B2 aluminides

An attempt is made to achieve inertia friction-welding in FeAl and NiAl samples, taking into account their intermetallics' compositions, extrusion parameters, and microstructural data. The energy required for the weld is stored in a rotating flywheel mass attached to one of the two pieces to be joined; when enough energy is introduced, the flywheel is disconnected and an axial load is applied which forces the spinning piece against the stationary one, converting the energy into heat by means of friction. Due to the inherent brittleness of the aluminides, a step-load program was used in which an initial, low-pressure heat buildup increased the work pieces' ductility.

Whittenberger, J. Daniel↗
NASA NTRS1998

The Evaluation of a Modified Chrome Oxide Based High Temperature Solid Lubricant Coating for Foil Gas Bearings

This paper describes the friction and wear performance of PS304, a modified chrome oxide based coating, for foil gas bearings. PS304 contains 60 wt% NiCr binder, 20 wt% Cr2O3 hardener, and 10 wt% each Ag, and BaF2/CaF2 lubricants. For evaluation, the coating is plasma spray deposited onto test journals which are slid against a superalloy partial arc foil bearing. The test load was 10 KPa (1.5 psi) and the bearings were run under start/stop cyclic conditions. The data show good wear performance of the bearing, especially at temperatures above 25 deg. C. Bearing friction was moderate (micron approx. or equal to 0.4) over the entire temperature range. Based upon the results obtained, the PS304 coating has promise for high temperature, oil-free turbomachinery applications.

DellaCorte, Chris↗
NASA NTRS1986

Galileo inflight friction identification for the scan platform control loop

Two types of friction identification algorithms (position-based and rate-based) are investigated in an attempt to better understand cone actuator inflight behavior in the Galileo scan platform pointing system. This investigation involves the measurement of the scan platform position (or rate) with respect to the stator following a platform slew maneuver. Inflight data collection by the spacecraft's sensors and subsequent ground-based data processing comprise the two major steps in the identification experiment. The proposed algorithms were capable of obtaining friction estimates within + or - 10 percent accuracy; hence, it is concluded that this inflight system identification technique can sufficiently tune the Galileo cone controller.

Ianculescu, G. D.↗
DOE OSTI2023

A constitutive model for sheared dense fiber suspensions

Here we propose a constitutive model to predict the viscosity of fiber suspensions, which undergoes shear thinning, at various volume fractions, aspect ratios, and shear stresses/rates. We calibrate the model using the data from direct numerical simulation and prove the accuracy by predicting experimental measurements from the literature. We use a friction coefficient decreasing with the normal load between the fibers to quantitatively reproduce the experimentally observed shear thinning in fiber suspensions. In this model, the effective normal contact force, which is directly proportional to the bulk shear stress, determines the effective friction coefficient. A rise in the shear stress reduces the effective friction coefficient in the suspension. As a result, the jamming volume fraction increases with the shear stress, resulting in a shear thinning in the suspension viscosity. Moreover, we extend the model to quantify the effects of fiber volume fraction and aspect ratio in the suspension. We calibrate this model using the data from numerical simulations for the rate-controlled shear flow. Once calibrated, we show that the model can be used to predict the relative viscosity for different volume fractions, shear stresses, and aspect ratios. The model predictions are in excellent agreement with the available experimental measurements from the literature. The findings of this study can potentially be used to tune the fiber size and volume fraction for designing the suspension rheology in various applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1991

Waves in Venus's middle and upper atmosphere - Implications of Pioneer Venus probe data above the clouds

This paper reevaluates Pioneer Venus probe data which show the presence of waves in Venus's middle and upper atmosphere. The data are extended to 138 km. Uncertainties in the temperature are typically about 0.1 times amplitude, supporting the reliability of large-amplitude oscillations approaching 40 K at 120 km. Growth rates above 100 km follow approximately the inverse square root of density and 'saturation' occurs. The waves then break at the 120 km level, providing a source for the 'friction' required in models to match the observed day-night temperature contrast in the lower thermosphere. The data correlated to an unexpected degree with temperatures from the Pioneer Venus orbiter atmospheric drag experiment. The observations lead to the suggestion that the thermospheric waves are solar-fixed, induced either by the major subsidence across the termination or as continuation upward of waves in the middle atmosphere.

Seiff, Alvin↗
NASA NTRS1998

Friction Stir Welding of Large Scale Cryogenic Tanks for Aerospace Applications

The Marshall Space Flight Center (MSFC) has established a facility for the joining of large-scale aluminum cryogenic propellant tanks using the friction stir welding process. Longitudinal welds, approximately five meters in length, have been made by retrofitting an existing vertical fusion weld system, designed to fabricate tank barrel sections ranging from two to ten meters in diameter. The structural design requirements of the tooling, clamping and travel system will be described in this presentation along with process controls and real-time data acquisition developed for this application. The approach to retrofitting other large welding tools at MSFC with the friction stir welding process will also be discussed.

Russell, Carolyn↗
DOE OSTI2025

A rheological model for loose sands with insights from DEM

A rheological model for loose granular media is developed to capture both solid-like and fluid-like responses during shearing. The proposed model is built by following the mathematical structure of an extended Kelvin–Voigt model, where an elastic spring and plastic slider act in parallel to a viscous damper. This arrangement requires the partition of the total stress into rate-independent and rate-dependent stress components. To model the solid-like behavior, a simple frictional plasticity model is adopted without modifications, thus contributing to the rate-independent stress. Instead, the fluid-like or rate-dependent stress is further decomposed into deviatoric and volumetric parts, by proposing a new formulation based on a combination of the μ(I) relation, originally developed under pressure-controlled shear, with a pressure-shear rate relation derived under volume-controlled shear. The proposed formulation allows the model to capture both the increase in the friction coefficient and the enhanced dilation at high shear rates. High-fidelity simulation data, obtained from discrete element method and multiscale modelling, are used to evaluate the performance of the proposed constitutive model. The model provides accurate results under both drained and undrained simple shear paths across a wide range of shear rates. Furthermore, it successfully reproduces at much lower computational cost the flowslide mobility computed through multiscale simulations, which is primarily regulated by the shear rate dependence of the material properties during the dynamic runout stage.

Elasticity↗
DOE OSTI2025

Generalizable Image Segmentation for Microstructure Characterization Through Integrated SEM and EBSD Analysis

We demonstrate generalizable semantic segmentation using minimal ground truth data. Correlated scanning electron microscopy (SEM) images and electron backscatter diffraction (EBSD) measurements of frictionstir processed 316L stainless steel plates were used to train deep learning models for grain boundary segmentation. Secondary electron (SE) imaging taken at an accelerating voltage of 10 keV correlated to EBSD-derived grain boundaries produced the best performing model. Notably, an ensemble of three models trained on a single SE image produced accurate segmentation over a series of BSE images of samples manufactured under different processing parameters, with a resultant mean absolute error in grain size of 0.34 µm. The striking generalizability of the models likely results from the similar escape depths of the SE training input and the EBSD training output and the reduced probability of dislocation artifacts appearing in the image. This finding highlights the importance of considering the physical principles behind imaging in the development of robust segmentation models for microstructure characterization.

Taufique, Mohammad Fuad Nur↗
DOE OSTI2020

Experimental Study on the Effect of Localized Blockages on the Friction Factor of a 61-Pin Wire-Wrapped Bundle

Abstract The thermal-hydraulic behavior of the flow in rod bundles has motivated numerous experimental and computational investigations. Previous studies have identified potential for accumulation of debris within the small subchannels of typical wire-wrapped assemblies with subsequent total or partial blockage of subchannel coolant flow. A test campaign was conducted to study the effects of localized blockages on the bundle averaged friction factor of a tightly packed wire-wrapped rod bundle. Blockages were installed within the bundle, and fluid pressure drop was measured across one wire pitch for a Reynolds number range of 500–17,200. The Darcy–Weisbach friction factor of the perturbed rod bundle geometry was compared with that of the unblocked bundle, as well as with the predictions of a well-established friction factor correlation. Differing effects based on blockage size and location for various flow regimes were studied. A number of conclusions can be made about the effects of the blockages on the friction factor, such as an increasing effect of the blockage on friction factor with an increase in Reynolds number, a change in flow behavior in the turbulent transition flow regime near Reynolds number 3000, differences in effect on friction factor for different types of subchannel blockage, and a nonlinear trend in friction factor variation with flow area impeded for edge subchannels. To this end, all data and quantified uncertainty produced in this study are made available for comparison and validation of advanced computational tools.

Engineering↗
NASA NTRS1967

A theoretical model for determining turbine flowmeter sensitivity

Analytical model of turbine-type flowmeter guides in the selection of valid extrapolation of available calibration data. An expression for flowmeter performance is developed to include the effects of fluid friction, bearing drag, and magnetic drag upon helical rotor design.

Smith, R. L.↗