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Results for “SURFACE ROUGHNESS EFFECT”

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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Ablation of Galileo Probe heat-shield models in a ballistic range

Several 1/24-scale models of the Galileo Probe made of carbon-phenolic materials were flown in a ballistic range to test their ablation characteristics. Mostly radiative or all-convective heating environments were produced by using argon or air as the test gas, respectively, to simulate the Jovian entry heating environments. The experimental results were compared with the theoretical predictions made using the computer codes of radiating shock layer environment (RASLE) and charring materials ablation (CMA). The experimental data obtained in argon agreed approximately with the theoretical predictions. The data for air agreed approximately with the theory when turbulence and surface roughness effects were accounted for. The data imply that the Galileo Probe heat shield was adequately designed.

Park, C.↗
NASA NTRS1986

Numerical simulation of the flowfield over ice accretion shapes

The primary goals are directed toward the development of a numerical method for computing flow about ice accretion shapes and determining the influence of these shapes on flow degradation. It is expedient to investigate various aspects of icing independently in order to assess their contribution to the overall icing phenomena. The specific aspects to be examined include the water droplet trajectories with collection efficiencies and phase change on the surface, the flowfield about specified shapes including lift, drag, and heat transfer distribution, and surface roughness effects. The configurations computed were models of ice accretion shapes formed on a circular cylinder in the NASA Lewis Icing Research Tunnel. An existing Navier-Stokes program was modified to compute the flowfield over four shapes (2, 5, and 15 minute models of glaze ice, and a 15 minute accumulation of rime ice).

Scott, J. N.↗
NASA NTRS1993

Spatial patterns in backscatter strength across the Greenland Ice Sheet

The relationship between the physical properties of the Greenland ice sheet and Synthetic Aperture Radar (SAR) data collected from aircraft and from ERS-1 is addressed. Limited aircraft data are combined with a description of the glacier surface to predict qualitatively the spatial and seasonal variation in backscatter strength across the ice sheet. In particular the model predicts relatively low backscatter near the ice edge where scattering is dominated by rough surface effects. Backscatter increases through the lake zone as volume scattering becomes important. Strongest backscatter is found in the percolation facies where volume scatter from snow grains and volume scatter from large, buried ice bodies becomes important. Backscatter weakens in the interior ice sheet where fine grained snow is the only mechanism producing backscatter.

Jezek, K. C.↗
NASA NTRS1994

Mid-infrared spectropolarimetry as a remote sensing tool

A preliminary investigation of mid-infrared spectropolarimetry as a new technique to accurately measure features in the thermal spectra of planetary regoliths is described. The 5- to 12-micron polarization of igneous rocks and powders commonly found on planetary surfaces is measured to explore the viability of this technique for future groundbased and space-based experiments. Mid-infrared polarization is found to be diagnostic of composition for both whole rock and sand samples, while exhibiting less interference from surface roughness effects than with mid-infrared spectrophotometry.

Johnson, Paul E.↗
NASA NTRS2011

Sea Surface Salinity and Wind Retrieval Algorithm Using Combined Passive-Active L-Band Microwave Data

Aquarius is a combined passive/active L-band microwave instrument developed to map the salinity field at the surface of the ocean from space. The data will support studies of the coupling between ocean circulation, the global water cycle, and climate. The primary science objective of this mission is to monitor the seasonal and interannual variation of the large scale features of the surface salinity field in the open ocean with a spatial resolution of 150 kilometers and a retrieval accuracy of 0.2 practical salinity units globally on a monthly basis. The measurement principle is based on the response of the L-band (1.413 gigahertz) sea surface brightness temperatures (T (sub B)) to sea surface salinity. To achieve the required 0.2 practical salinity units accuracy, the impact of sea surface roughness (e.g. wind-generated ripples and waves) along with several factors on the observed brightness temperature has to be corrected to better than a few tenths of a degree Kelvin. To the end, Aquarius includes a scatterometer to help correct for this surface roughness effect.

ocean salinity↗
NASA NTRS2018

Characterization and Analysis of Phoca Vitulina, Zalophus Californianus and Mirounga Angustirostris Vibrissae

Vibrissae of Phoca Vitulina (harbor seal) and Mirounga Angustirostris (elephant seal) possess undulations along their length. Harbor seal vibrissae have shown potential to reduce vortex induced vibrations and reduce drag compared to cylinders and ellipses. The exact geometry of the whiskers has not been well documented and the parameters that are responsible for the reduction in drag and vortex induced vibrations have not been characterized. Samples of six harbor seal vibrissae, six elephant seal vibrissae and six California sea lion (Zalophus californianus) vibrissae were collected from the Marine Mammal Center in California. The objectives of this study were to (1) Compare measurement techniques for digitizing and extracting parameters of the seal whiskers for the PeTaL (Periodic Table of Life) database. CT scanning, microscopy and 3D scanning techniques were compared. (2) Compare aerodynamic characteristics of a representative harbor seal whisker, elephant seal whisker, California sea lion whisker and ellipse at Re = 12000 and Re = 23000 based on major axis and free stream velocity. The data (in appendices) is available to compare CFD models or for further experimental validation, (3) Show close up images of whiskers and look for surface roughness effects. Variations in the seven parameters of the seal whisker were observed that may either be a feature of the vibration reduction mechanism or a result of natural variation. It is hypothesized that six parameters are sufficient to characterize seal whiskers based on analytic fitting. The drag coefficient of harbor seal whiskers examined in this study were found to be 25 percent lower than that of an ellipse with comparable major and minor axis lengths at Reynolds number of 12000. The dissipation length scale was found to be larger for seal whiskers. Potential applications of seal whisker morphology for aerospace are discussed. Roughness is not thought to play a factor in seal hydrodynamics.

Shyam, Vikram↗
NASA NTRS2021

Development of Spaceborne SoOp Reflectometry Model for Complex Terrains

Following the launch of multiple global navigation satel-lite system (GNSS) reflectometry (GNSS-R) missions, theSignals of Opportunity (SoOp) method has proven to be apowerful tool for geophysical parameter retrieval for land ap-plications such as soil moisture. Having demonstrated thefeasibility of the SoOp techniques at P- and S-band, the devel-opment of SoOp measurements beyond the GNSS frequencyregime is highly anticipated. The SoOp Coherent Bistatic(SCoBi) model and simulator, developed in 2017 and open-sourced in 2018, has been made available to provide multi-frequency, fully polarimetric SoOp simulations for ground-based applications through the joint use of analytical wavetheory and distorted Borne approximation to evaluate landcontributions from multilayer dielectric profiles composed ofsoil moisture, vegetation, and surface roughness effects. Thispaper describes the advancement of SCoBi from a ground-and airborne-based model to a spaceborne model. This ex-tension allows for fully polarimetric, complex delay-Dopplermap (DDM) simulations through evaluation of the coherentsuperposition of electric fields emerging from a grid of ori-ented facets. The model generates a grid of facets by de-termining the geometry of contributing elements from digitalelevation models, with each element providing its contribu-tion under a flat-earth assumption. This module will enablethe analysis of fully polarimetric scattering from frequenciesavailable across the ultra-high frequency (UHF) regime.

D R Boyd↗
NASA NTRS2022

Development of SMAP Retrievals for Forested Regions: SMAPVEX19-22 and SMAPVEX22-Boreal

The retrieval of soil moisture (SM) under forest canopy has long been an important goal for low frequency remote sensing. The NASA Soil Moisture Active Passive (SMAP) mission is engaged at three separate experiment sites to improve its SM retrieval algorithm in forested areas. Two of the sites are located in the deciduous forest region in Massachusetts and New York, US and one is located in southern boreal forest zone in Saskatchewan, Canada. Each site has a SM measurement network of about 20 stations spread out over an area of about 30 km, which covers the SMAP radiometer footprint. In 2022, intensive observations will be carried out at each site which involve deployments of an airborne instrument, which is similar to the SMAP instrument, and intensive manual measurements of SM, surface and vegetation. The measurements also include tower-based radiometer observations with ground truth measurements within the instrument footprint. Here we show some early results using the networks and SMAP measurements to analyze the sensitivity of the SMAP L-band measurements to SM changes in forested area and the impact of the vegetation to the signal. The results suggest an upper limit for vegetation attenuation accounting for surface roughness effect and relate that to the values used in the current SMAP SM products.

Yueh, Simon H.↗
NASA NTRSDate not supplied

An Overview of the Aerothermodynamic Database for the Mars Sample Return Earth Entry Vehicle

The Mars Sample Return Earth Entry System (MSR-EES) is a capsule that is part of the Mars Sample Return mission that will return Martian soil samples to Earth in 2033. Due to the steep flight path angle and relatively large vehicle size, the MSR-EES capsule will experience the highest peak heating rate of any previous Earth entry vehicle. The aerothermal database for MSR-EES is primarily characterized by numerical CFD, DSMC, and radiation simulations. Margins are applied to the convective and radiative heating rates. Surface roughness effects and margins are also included in the database formulation. The aerothermal database can be used to extract information at any body point location, perform trade studies in trajectory space, and provide inputs for material response simulations.

Mars↗
NASA NTRS1996

Scuffing Characteristics of High-Load Rolling/Sliding Contacts Operating in Liquid Oxygen: Effects of Materials and Surface Roughness

This research reports on an experimental study of the effects of materials and surface roughness on the scuffing characteristics of rolling/sliding contacts cooled and lubricated with liquid oxygen. Experiments were carried out under heavy loading with a Hertzian pressure in the range of 2.0 GPa to 3.0 GPa and with a high rolling velocity of up to 48 m/s. For contacts between AISI 440 C stainless-steel elements, the results showed that the scuffing behavior of the system was fairly consistent under a wide range of rolling velocity. Scuffing commenced at a small slide-to-roll ratio of around 0.02, and the scuffing behavior of the contact was not sensitive to surface roughness for the test-sample RMS roughness ranging from 0.02 microns to 0.10 microns. For contacts between 440 C and Si3N4 elements, on the other hand, the scuffing behavior of the system was not very consistent and somewhat unpredictable. The results were sensitive to surface roughness particularly that of the Si3N4 test sample. With well polished test samples, consistent results were obtained; the level of traction was lower than that with a 440 C toroid and scuffing did not take place up to a slide-to-roll ratio of near 0.03. The results strongly suggest that significant hydrodynamic effect can be generated by liquid oxygen under heavy loading and high velocity conditions. The results also suggest that the hydrodynamic action is likely generated by the conventional viscous mechanism as it can be largely destroyed by a narrow circumferential surface scratch running through the central region of the contact.

Chang, L.↗
NASA NTRS1991

Two-dimensional Navier-Stokes heat transfer analysis for rough turbine blades

A quasi-three-dimensional thin-layer Navier-Stokes analysis was used to predict heat transfer to rough surfaces. Comparisons are made between predicted and experimental heat transfer for turbine blades and flat plates of known roughness. The effect of surface roughness on heat transfer was modeled using a mixing length approach. The effect of near-wall grid spacing and convergence criteria on the accuracy of the heat transfer predictions are examined. An eddy viscosity mixing length model having an inner and outer layer was used. A discussion of the appropriate model for the crossover between the inner and outer layers is included. The analytic results are compared with experimental data for both flat plates and turbine blade geometries. Comparisons between predicted and experimental heat transfer showed that a modeling roughness effects using a modified mixing length approach results in good predictions of the trends in heat transfer due to roughness.

Boyle, R. J.↗
NASA NTRS1991

Two-dimensional Navier-Stokes heat transfer analysis for rough turbine blades

A quasi-three-dimensional thin-layer Navier-Stokes analysis was used to predict heat transfer to rough surfaces. Comparisons are made between predicted and experimental heat transfer for turbine blades and flat plates of known roughness. The effect of surface roughness on heat transfer was modeled using a mixing length approach. The effect of near-wall grid spacing and convergence criteria on the accuracy of the heat transfer predictions are examined. An eddy viscosity mixing length model having an inner and outer layer was used. A discussion of the appropriate model for the crossover between the inner and outer layers is included. The analytic results are compared with experimental data for both flat plates and turbine blade geometries. Comparisons between predicted and experimental heat transfer showed that a modeling roughness effects using a modified mixing length approach results in good predictions of the trends in heat transfer due to roughness.

Boyle, R. J.↗
NASA NTRS1972

Temperature of the rough lunar surface.

The effect of lunar surface roughness on the lunar surface temperatures is investigated. It is shown that the apparent surface temperature varies significantly according to the observation angle at a given solar elevation. This is due to the surface roughness which is postulated as a level surface interspersed with craters. The temperatures of craters and flat surfaces are obtained analytically. The apparent temperature is the result of the contribution of craters and flat regions whose ratio is derived from earth-based measurements. The results are compared with experimental data.

Adorjan, A. S.↗
NASA NTRS2006

An Analytical Solution of Radiative Transfer in the Coupled Atmosphere-Ocean System with Rough Surface

Using the efficient discrete-ordinate method, we present an analytical solution for radiative transfer in the coupled atmosphere-ocean system with rough air-water interface. The theoretical formulations of the radiative transfer equation and solution are described. The effects of surface roughness on radiation field in the atmosphere and ocean are studied and compared with measurements. The results show that ocean surface roughness has significant effects on the upwelling radiation in the atmosphere and the downwelling radiation in the ocean. As wind speed increases, the angular domain of sunglint broadens, the surface albedo decreases, and the transmission to ocean increases. The downward radiance field in the upper ocean is highly anisotropic, but this anisotropy decreases rapidly as surface wind increases and as depth in ocean increases. The effects of surface roughness on radiation also depend greatly on both wavelength and angle of incidence (i.e., solar elevation); these effects are significantly smaller throughout the spectrum at high sun. The model-observation discrepancies may indicate that the Cox-Munk surface roughness model is not sufficient for high wind conditions.

Jin, Zhonghai↗
NASA NTRS1987

The effects of soil moisture, surface roughness, and vegetation on L-band emission and backscatter

Measurements performed with SIR-B at 1.28 GHz and an airborne multiple-beam push-broom radiometer at 1.4 GHz over agricultural fields near Fresno, California are examined. A theoretical model (Kirchhoff approximation) was used to assess the effects of surface roughness and vegetation (alfalfa and lettuce) with respect to the responses of microwave emission and backscatter to soil-moisture variations. It is found that the surface roughness plays a dominant role compared to the vegetation cover in the microwave backscatter.

Wang, James R.↗