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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 163 records · Page 9
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NASA NTRSDate not supplied

Design of a Propeller with Global Minimum Torque

Academia, industry, and Government are actively working towards a future where dozens of small to large Unmanned Aerial Systems (UAS) are present within urban environments. In this environment, high noise pollution and inefficiencies have the potential to render these new technologies impractical due to public annoyance and nonacceptance. This study aims to design and analyze a novel propeller design for minimum global torque using an optimization algorithm to find the full three dimensional solution of maximum efficiency. This resulted in a 𝐶 𝑙 distribution defining the global minimum torque solution for propeller design which corresponded with moving as much lift inboard as possible and reducing lift rapidly at the blade tip. The novel propeller (dubbed "Prandtl" propeller) was then compared with the current gold standard in propeller design, a minimum induced loss (MIL) propeller, which had all the same geometric properties except for blade twist and produced the same amount of thrust at the same advance ratio. The results of multiple iterations of Prandtl propellers showed an increase in efficiency of 2.0-3.3% for the Prandtl blade when compared to the equivalent MIL blade. A potential added benefit of this blade design is lower noise generation due to the lower lift loading at the tip reducing the large shear layer intensity which is the point source of noise in propellers. Two major breakthroughs for enabling widespread use of UAS in urban environments are noise reduction and vehicle efficiency, and this new propeller design has the potential to provide both.

Propeller↗
NASA NTRSDate not supplied

Geometric Assessment of PlanetScope Imagery

Commercial companies such as Maxar, Planet Labs, and BlackSky have built large archives of high resolution (1-3 m) Earth observing data. The high temporal resolution and global coverage of these satellites makes commercial satellite images ideal for scientists studying rapidly changing processes such as flooding and fires. The high spatial resolution allows scientists to push studies to a fine scale such as monitoring agricultural growth experiments or detecting vehicles for traffic management. Scientists using these data need to know geolocation accuracy, band-to-band registration (BBR), and pixel footprint size to best determine appropriate applications as well as what extra steps they will need to take to use the data. Here, we find those key geometric properties for images from Planet Labs’ SuperDove constellation. Geolocation accuracy is assessed relative to WorldView images at globally distributed cities, band-to-band registration (BBR) is examined for every image we acquired (200+ images), and pixel footprint sizes are calculated from edge responses of the images over Cal/Val sites in China, India, or USA both near launch time and 1+ years after launch. We find that SuperDove geolocation is highly self-consistent with average global offsets among SuperDove images of 3.80 m (1.27 pixels). Despite this self-consistency, relative geolocation accuracy (with WorldView images as reference) varies by location from 3.20 m – 28.09 m mean offset. SuperDove BBR is sub-pixel and varies by band, with a mean radial offset relative to red band varying from 0.39 - 1.13 m. SuperDove image footprint size improves after 1+ years in orbit, with an average footprint size of 3.41 pixels (10.24 m) soon after launch and 3.23 pixels (9.7 m) 1+ years after launch. The BBR and self-consistency offsets are relatively small, given the large footprint sizes. A similarly extensive investigation is in progress for Planet Labs’ Dove-R series.

Alana G. Semple↗
NASA NTRS2024

Vertical Structure of Gas and Dust in Four Debris Disks

We present high-spectral-resolution M-band spectra from iSHELL on NASA’s Infrared Telescope Facility along the line of sight to the debris disk host star HD 32297. We also present a Gemini Planet Imager H-band polarimetric image of the HD 131488 debris disk. We search for fundamental CO absorption lines in the iSHELL spectra of HD 32297, but do not detect any. We place an upper limit on the CO column density of ∼6×1015cm−2. By combining the column density upper limit, the CO mass measured with the Atacama Large Millimeter/submillimeter Array (ALMA), and the geometrical properties of the disk, we estimate the scale height of the CO to be 2au across the radial extent of the disk (∼80–120au). We use the same method to estimate the CO scale height of three other edge-on, CO-rich debris disks that all have CO observed in absorption with the Hubble Space Telescope as well as in emission with ALMA: β Pictoris, HD 110058, and HD 131488. We compare our estimated CO scale heights of these four systems to the millimeter dust scale heights and find that, under the assumption of hydrostatic equilibrium, there is a potential correlation between the CO and millimeter dust scale heights. There are multiple factors that affect the gas vertical structure such as turbulence, photodissociation with weak vertical mixing, as well as where the gas originates. One possible explanation for the potential correlation could be that the gas and dust are of a similar secondary origin in these four systems.

Kadin Worthen↗
NASA NTRS1983

Geometric and structural properties of a rectangular supercritical wing oscillated in pitch for measurement of unsteady transonic pressure distributions

Wind-tunnel tests to measure unsteady aerodynamic data in the transonic region have been completed on an aspect ratio 2.0 rectangular wing with a supercritical airfoil. The geometric and structural properties of the wing are presented. (Other references contain the measured aerodynamic data.) Both measured and design airfoil coordinates are presented and compared. In addition, measured wing bending and torsional stiffness distributions and some trailing-edge flexibility influence coefficients are presented.

Ricketts, R. H.↗
NASA NTRS1989

Geometrical and structural properties of an Aeroelastic Research Wing (ARW-2)

Transonic steady and unsteady pressure tests were conducted on a large elastic wing known as the DAST ARW-2 wing. The wing has a supercritical airfoil, an aspect ratio of 10.3, a leading edge sweepback angle of 28.8 deg and is equipped with two inboard and one outboard trailing edge control surfaces. The geometrical and structural characteristics are presented of this elastic wing, using a combination of measured and calculated data, to permit future analyst to compare the experimental surface pressure data with theoretical predictions.

Sandford, Maynard C.↗
NASA NTRS1990

Changes in geometrical and biomechanical properties of immature male and female rat tibia

The differences in the geometry and mechanical properties of immature male and female rat tibiae were detailed in order to provide comparative data for spaceflight, exercise, or disease experiments that use immature rats as an animal model. The experiment focuses on the particularly rapid period of growth that occurs in the Sprague-Dawley rat between 40 and 60 d of age. Tibial length and middiaphysical cross-sectional data were analyzed for eight different groups of rats according to age and sex, and tibial mechanical properties were obtained via three-point bending tests to failure. Results indicate that, during the 15 d period of rapid growth, changes in rat tibial geometry are more important than changes in bone material properties for influencing the mechanical properties of the tibia. Male tibiae changed primarily in structural properties, while in the female rats major changes in mechanical properties of the tibia were only attributable to changes in the structural properties of the bone.

Zernicke, Ronald F.↗
NASA NTRS1971

Computer program for thermal analysis of shadow shields in a vacuum

Computer program determines temperature profiles and heat transfer rates for shadow shielded cryogenic tank. Tank, shields, and thermal radiation heat source are all axisymmetric. Thermal analysis considers varying shield and tank temperatures, surface properties, and geometric arrangements. Similar heat source properties are also considered.

Boyle, R. J.↗
NASA NTRS1974

Analytical study of rigidized fibrous materials

Insulation systems composed of micrometer-sized fibers bonded together with small amounts of binder have been developed for aerospace applications. The materials have a very high volid content and low density and can be characterized as a rigidized network of fibers randomly oriented in three-dimensional space. Analytical models suitable for the evaluation of the mechanical behavior of rigidized fibrous materials have been developed. The models treat the material as a space frame structure and includes the effects of joint fixity and fiber curvature. The geometrical and material property variabilities are represented by a number of trusses oriented in five planes. Each truss may have different material and geometric properties. Techniques have been developed to describe the continuous material property and geometry functions as a series of descrete quantities that can be used to describe each of the trusses in the model. Parametric studies were performed to show the influence of material variables on the mechanical behavior of the material. Results of calculations show good agreement with measured properties.

Rosen, B. W.↗
NASA NTRS1987

The 1986 DA and 1986 EB: M-class asteroids in near-Earth orbits

The Earth-approaching asteroid population is composed of asteroids in orbits with short lifetimes compared with the age of the solar system. These objects which are comprised of Aten, Apollo, and Amor asteroids must be replenished from either cometary or mainbelt asteroid sources since lifetimes against collision with or ejection by a planet are on the order of 10 to 100 million years. The physical study of Earth-approaching asteroids is constrained by the generally long period between favorable apparitions and poorly known orbits. Broadband spectrophotometry on the Johnson UBVR system and the Eight-Color Asteroid Survey system were obtained at Kitt Peak National Observatory and on the Johnson JHK system and at 10 and 20 microns at the NASA Infrared Telescope Facility at Mauna Kea Observatory. These observations were used to determine the absolute visual magnitudes and to derive the visual geometric albedos and diameters on the IRAS system. The spectral reflectance properties and geometric albedos of the M-class asteroids are consistent compositions analogous to the iron nickel meteorites or the enstatite-metal assemblages of the enstatite chondrites. The issue of the source(s) of the near-Earth asteroids population was examined by comparing the classifications on the scheme employed by Gradie and Tedesco of 38 such asteroids. Most of the near-Earth objects is indeed the asteroid belt as the observations suggest, then a method for removing extinct nuclei of short period comets must be found since the rate of production of short period comets from the long period comets is relatively large.

Gradie, Jonathan↗
NASA NTRS1983

The effects of vegetation and soil hydraulic properties on passive microwave sensing of soil moisture: Data report for the 1982 fiels experiments

Field experiments to (1) study the biomass and geometrical structure properties of vegetation canopies to determine their impact on microwave emission data, and (2) to verify whether time series microwave data can be related to soil hydrologic properties for use in soil type classification. Truck mounted radiometers at 1.4 GHz and 5 GHz were used to obtain microwave brightness temperatures of bare vegetated test plots under different conditions of soil wetness, plant water content and canopy structure. Observations of soil moisture, soil temperature, vegetation biomass and other soil and canopy parameters were made concurrently with the microwave measurements. The experimental design and data collection procedures for both experiments are documented and the reduced data are presented in tabular form.

Oneill, P.↗
NASA NTRS2005

Comparison of Elevated Temperature Tensile Properties and Fatigue Behavior of Two Variants of a Woven SiC/SiC Composite

Tensile properties (elastic modulus, proportional limit strength, in-plane tensile strength, and strain at failure) of two variants of a woven SiC/SiC composite, manufactured during two separate time periods (9/99 and 1/01), were determined at 1038 and 1204 C by conducting tensile tests on specimens machined from plates. Continuous cycling fatigue tests (R = 0.05) and 20 cpm) were also conducted at the same two temperatures on specimens from both composites. In this study, average tensile properties, 95% confidence intervals associated with the tensile properties, and geometric mean fatigue lives of both composite materials are compared. The observed similarities and differences in the tensile properties are highlighted and an attempt is made to understand the relationship, if any, between the tensile properties and the fatigue behaviors of the two woven composites.

Kalluri, Sreeramesh↗
NASA NTRS1983

The use of thematic mapper data for land cover discrimination: Preliminary results from the UK SATMaP programme

The principal objectives of the UK SATMaP program are to determine thematic mapper (TM) performance with particular reference to spatial resolution properties and geometric characteristics of the data. So far, analysis is restricted to images from the U.S. and concentrates on spectra and radiometric properties. The results indicate that the data are inherently three dimensional compared with the two dimensional character of MSS data. Preliminary classification results indicate the importance of the near infrared band (TM 4), at least one middle infrared band (TM 5 or TM 6) and at least one of the visible bands (preferably either TM 3 or TM 1). The thermal infrared also appears to have discriminatory ability despite its coarser spatial resolution. For band 4 the forward and reverse scans show somewhat different spectral responses in one scene but this effect is absent in the other analyzed. From examination of the histograms it would appear that the full 8-bit quantization is not being effectively utilized for all the bands.

Jackson, M. J.↗
NASA NTRS1985

The Use of Thematic Mapper Data for Land Cover Discrimination: Preliminary Results from the UK Satmap Programme

The principal objectives of the UK SATMaP program are to determine thematic mapper (TM) performance with particular reference to spatial resolution properties and geometric characteristics of the data. So far, analysis is restricted to images from the U.S. and concentrates on spectra and radiometric properties. The results indicate that the data are inherently three dimensional compared with the two dimensional character of MSS data. Preliminary classification results indicate the importance of the near infrared band (TM 4), at least one middle infrared band (TM 5 or TM 6) and at least one of the visible bands (preferably either TM 3 or TM 1). The thermal infrared also appears to have discriminatory ability despite its coarser spatial resolution. For band 4 the forward and reverse scans show somewhat different spectral responses in one scene but this effect is absent in the other analyzed. From examination of the histograms it would appear that the full 8 bit quantization is not being effectively utilized for all the bands.

Jackson, M. J.↗
NASA NTRS1979

Thermal stress analysis of ceramic gas-path seal components for aircraft turbines

Stress and temperature distributions were evaluated numerically for a blade-tip seal system proposed for gas turbine applications. The seal consists of an abradable ceramic layer on metallic backing with intermediate layers between the ceramic layer and metal substrate. The most severe stresses in the seal, as far as failure is concerned, are tensile stresses at the top of the ceramic layer and shear and normal stresses at the layer interfaces. All these stresses reach their maximum values during the deceleration phase of a test engine cycle. A parametric study was carried out to evaluate the influence of various design parameters on these critical stress values. The influences of material properties and geometric parameters of the ceramic, intermediate, and backing layers were investigated. After the parametric study was completed, a seal system was designed which incorporated materials with beneficial elastic and thermal properties in each layer of the seal. An analysis of the proposed seal design shows an appreciable decrease in the magnitude of the maximum critical stresses over those obtained with earlier configurations.

Kennedy, F. E.↗
NASA NTRS1976

Correlation of freestream pressure disturbances in supersonic wind tunnels

An attempt is made to correlate data for freestream disturbance levels in terms of parameters that can be easily calculated for most wind tunnels. A correlation expression is derived assuming that the fluctuating pressure at the wall of the supersonic wind tunnel are related to fluctuating pressures in the freestream. The acoustic origins, flow properties, and geometric factors are taken into account. The suggested correlations of wind tunnel disturbances provide good predictions of rms pressure disturbances in the freestream of wind tunnels or on the surface of cones at Mach numbers greater than 2.5.

Stainback, P. C.↗