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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 145 records · Page 8
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NASA NTRS1993

Turbulence near thunderstorm tops

For several years, scientists at San Jose State University, NASA-Ames, and the University of Arizona have carried out cooperative research programs to understand the causes and effects of severe turbulence. The primary sources of data for this work are Digital Flight Data Recorder (DFDR) tapes from airliners that have been involved in turbulence incidents. A significant result of the analysis of these data has been the identification and quantification of the turbulence causes. Turbulence signatures include breaking Kelvin-Helmholtz waves, large amplitude mountain lee waves, turbulence in and around thunderstorms, and maneuvering. The requirements that must be met for a turbulence incident to be included in the NASA study are rather straightforward: (1) severe or greater turbulence must have been reported (usually with passenger injuries) and (2) the flight data tapes must be available. Despite these rather general criteria, and the fact that our cases are drawn from a wide geographical area over the U.S. and the Atlantic Ocean, we have found an interesting bias in our sample. Of 12 cases at cruise altitude, four were definitely associated with thunderstorms and two are suspected thunderstorm cases. The others were due to mountain waves, CAT, high level windshear/maneuvering, or to causes not yet determined. Although our sample is small, these numbers have raised several questions, not the least of which are: How pervasive is the problem of aircraft encounters with severe turbulence in or near thunderstorm tops (TNTT)? Given the available visible and radar evidence of thunderstorms, Why do such incidents occur? Can anything be done to allevaite the problem? This paper outlines some very preliminary efforts to answer these questions. In the following sections, physical and statistical characteristics of TNTT are discussed (Section 2), TNTT causes are summarized (Section 3), current recommendations for TNTT avoidance are reviewed (Section 4), and some suggestions to ameliorate the problem are given (Section 5).

Lester, Peter F.↗
NASA NTRS1995

Numerical Studies of Boundary-Layer Receptivity

Direct numerical simulations (DNS) of the acoustic receptivity process on a semi-infinite flat plate with a modified-super-elliptic (MSE) leading edge are performed. The incompressible Navier-Stokes equations are solved in stream-function/vorticity form in a general curvilinear coordinate system. The steady basic-state solution is found by solving the governing equations using an alternating direction implicit (ADI) procedure which takes advantage of the parallelism present in line-splitting techniques. Time-harmonic oscillations of the farfield velocity are applied as unsteady boundary conditions to the unsteady disturbance equations. An efficient time-harmonic scheme is used to produce the disturbance solutions. Buffer-zone techniques have been applied to eliminate wave reflection from the outflow boundary. The spatial evolution of Tollmien-Schlichting (T-S) waves is analyzed and compared with experiment and theory. The effects of nose-radius, frequency, Reynolds number, angle of attack, and amplitude of the acoustic wave are investigated. This work is being performed in conjunction with the experiments at the Arizona State University Unsteady Wind Tunnel under the direction of Professor William Saric. The simulations are of the same configuration and parameters used in the wind-tunnel experiments.

Reed, Helen L.↗
NASA NTRS1995

Hybrid laminar flow control experiments in the NASA - Ames, 11-foot tunnel

It was proposed to design and conduct experiments in the NASA-Ames Research Center, 11-foot wind tunnel, that would assess the role of freestream turbulence and surface roughness on swept-wing transition to turbulence. The work was to be a cooperative effort that had direct application to hybrid laminar flow control (HLFC) airfoils. The first part of the proposed work, initiated in FY92 and continued into FY93, concentrated on the design of such an experiment whose results may be compared with results obtained in other wind-tunnel facilities. At the same time, concurrent work in the Arizona State University (ASU) Unsteady Wind Tunnel would be conducted on the effects of surface roughness. The second part of the work, which was to be initiated in FY94, would have consisted of experiments conducted in both the 11-foot tunnel at NASA-Ames and the ASU Unsteady Wind Tunnel. However, this work was not continued. This report summarizes the experimental design considerations and some preliminary experiments that made up the first part of the work.

Saric, William S.↗
NASA NTRS1996

Control of Unstable Waves in Three Dimensional Boundary Layers

Stability experiments are conducted in the Arizona State University Unsteady Wind Tunnel on a 45 deg. swept airfoil. The pressure gradient is designed to provide purely crossflow-dominated transition; that is, the boundary layer is subcritical to Tollmien- Schlichting (T-S) disturbances. The airfoil surface is hand polished to a 0.25 micron rms finish. Under these conditions, stationary crossflow disturbances grow to nonuniform amplitude due to submicron surface irregularities near the leading edge. Spectral de-compositions isolate single-mode growth rates for the fundamental and harmonic disturbances. The measurements show early nonlinear growth causing amplitude saturation well before transition. Comparisons with nonlinear PSE calculations show excellent agreement in both the amplitude saturation and the disturbance mode shape.

Saric, William S.↗
NASA NTRS1993

Effect of sound on boundary layer stability

Experiments are conducted in the Arizona State University Unsteady Wind Tunnel with a zero-pressure-gradient flat-plate model that has a 67:1 elliptical leading edge. Boundary-layer measurements are made of the streamwise fluctuating-velocity component in order to identify the amplified T-S waves that are forced by downstream-travelling, sound waves. Measurements are taken with circular 3-D roughness elements placed at the Branch 1 neutral stability point for the frequency under consideration, and then with the roughness element downstream of Branch 1. These roughness elements have a principal chord dimension equal to 2(lambda)(sub TS)/pi, of the T-S waves under study and are 'stacked' in order to resemble a Gaussian height distribution. Measurements taken just downstream of the roughness (with leading-edge T-S waves, surface roughness T-S waves, instrumentation sting vibrations and the Stokes wave subtracted) show the generation of 3-D-T-S waves, but not in the characteristic heart-shaped disturbance field predicted by 3-D asymptotic theory. Maximum disturbance amplitudes are found on the roughness centerline. However, some near-field characteristics predicted by numerical modelling are observed.

Saric, William S.↗
NASA NTRS1996

Naval Research Laboratory's programs in advanced indium phosphide solar cell development

The Naval Research Laboratory (NRL) has been involved in the development of solar cells for space applications since the 1960s. It quickly became apparent in this work that radiation damage caused to solar cells by electrons and protons trapped by the earth's magnetic field would seriously degrade the power output of photovoltaic arrays in extended missions. Techniques were therefore developed to harden the cells by shielding them with coverglass, etc. Ultimately, however, there is a limit to such approaches, which is determined by the radiation response of the semiconductor material employed. A desire for high efficiency and radiation resistance led to the development of alternative cell technologies such as GaAs, which has since become the technology of choice for many applications. InP cells are currently the most radiation resistant, high efficiency, planar cells known. NRL first sponsored InP solar cell technology in 1986, when Arizona State University was contracted to grow p/n cells by liquid phase epitaxy. NRL's interest in InP cells was generated by the results presented by Yamaguchi and his co-workers in the early 1980s on the remarkable radiation resistance of cells grown by diffusion of S into Zn doped p-type InP substrates. These cells also had beginning of life (BOL) efficiencies approximately 16%(AM0). Related to the radiation resistance of the cells was the fact that radiation-induced damage could be optically annealed by sunlight. Relatively large quantities of 1 x 2 cm(exp 2) diffused junction cells were made and were used on the MUSES-A and the EXOS-D satellites. These cells were also available in the U.S. through NIMCO, and were studied at NRL and elsewhere. Workers at NASA Lewis became involved in research in InP cells about the same time as NRL.

Summers, Geoffrey P.↗
NASA NTRS1997

Distributed-Roughness Effects on Stability and Transition In Swept-Wing Boundary Layers

Boundary-layer stability experiments are conducted in the Arizona State University Unsteady Wind Tunnel on a 45 deg swept airfoil. The pressure distribution and test conditions are designed to suppress Tollmien-Schlichting disturbances and provide crossflow-dominated transition. The surface of the airfoil is finely polished to a near mirror finish. Under these conditions, submicron surface irregularities cause the naturally occurring stationary crossflow waves to grow to nonuniform amplitudes. Spanwise-uniform stationary crossflow disturbances are generated through careful control of the initial conditions with full-span arrays of micron-high roughness elements near the attachment line. Detailed hot-wire measurements are taken to document the stationary crossflow structure and determine growth rates for the total and individual-mode disturbances. Naphthalene flow visualization provides transition location information. Roughness spacing and roughness height are varied to examine the effects on transition location and all amplified wavelengths. The measurements show that roughness spacings that do not contain harmonics equal to the most unstable wavelength as computed by linear stability theory effectively suppress the most unstable mode. Under certain conditions, subcritical roughness spacing delays transition past that of the corresponding smooth surface.

Carrillo, Ruben B., Jr.↗
NASA NTRS1996

Scientific Assessment of NASA's Solar System Exploration Roadmap

At its June 24-28, 1996, meeting, the Space Studies Board's Committee on Planetary and Lunar Exploration (COMPLEX), chaired by Ronald Greeley of Arizona State University, conducted an assessment of NASA's Mission to the Solar System Roadmap report. This assessment was made at the specific request of Dr. Jurgen Rahe, NASA's science program director for solar system exploration. The assessment includes consideration of the process by which the Roadmap was developed, comparison of the goals and objectives of the Roadmap with published National Research Council (NRC) recommendations, and suggestions for improving the Roadmap.

Source record↗
NASA NTRS1997

Galileo Net Flux Radiometer Report 1997

On 7 December 1995, the Galileo probe entered Jupiter's atmosphere. The Net Flux Radiometer (NFR) on board the probe, measured upward and downward fluxes in the visible and infrared. At the University of Arizona, we have analyzed the data from the two visible-light channels, as well as the solar contributions to the thermal channels. The results are being prepared for submission to JGR in early September.

Tomasko, Martin G.↗
NASA NTRS1997

New Research by CCD Scanning for Comets and Asteroids

Spacewatch was begun in 1980; its purpose is to explore the various populations of small objects within the solar system. Spacewatch provides data for studies of comets and asteroids, finds potential targets for space missions, and provides information on the environmental problem of possible impacts. Moving objects are discovered by scanning the sky with charge-coupled devices (CCDS) on the 0.9-meter Spacewatch Telescope of the University of Arizona on Kitt Peak. Each Spacewatch scan consists of three drift scan passes over an area of sky using a CCD filtered to a bandpass of 0.5-1.0 pm (approximately V+R+I with peak sensitivity at 0.7 pm). The effective exposure time for each pass is 143 seconds multiplied by the secant of the declination. The area covered by each scan is 32 arcminutes in declination by about 28 minutes of time in right ascension. The image scale is 1.05 arcseconds per pixel. Three passes take about 1.5 hours to complete and show motions of individual objects over a one hour time baseline. The limiting magnitude is about 21.5 in single scans. CCD scanning was developed by Spacewatch in the early 1980s, with improvements still being made - particularly by bringing a new 1.8-m Spacewatch Telescope on line. In the meantime, we have been finding some 30,000 new asteroids per year and applying their statistics to the study of the collisional history of the solar system. Spacewatch had found a total of 150 Near-Earth Asteroids (NEAS) and 8 new comets, and had recovered one lost comet (P/Spitaler in 1993). Spacewatch is also efficient in recovery of known comets and has detected and reported positions for more than 137,000 asteroids, mostly new ones in the main belt, including more than 10,882 asteroids designated by the Minor Planet Center (MPC).

Gehrels, Tom↗
NASA NTRS1998

Swept-Wing Receptivity Studies Using Distributed Roughness

This paper reviews the important recent progress in three-dimensional boundary-layer transition research. The review focuses on the crossflow instability that leads to transition on swept wings with a favorable pressure gradient. Following a brief overview of swept-wing instability mechanisms and the crossflow problem, a summary of the important findings of the 1990s is given. The discussion is presented from the experimental viewpoint, highlighting the ITAM work of Kachanov and co-workers, the DLR experiments of Bippes and co-workers, and the Arizona State University (ASU) investigations of Saric and co-workers. Where appropriate, relevant comparisons with CFD are drawn. The recent (last 18 months) research conducted by the ASU team is described in more detail in order to underscore the latest developments concerning nonlinear effects and transition control.

Saric, William S.↗
NASA NTRS1998

Effects of Suction on Swept-Wing Transition

Stability experiments are conducted in the Arizona State University Unsteady Wind Tunnel on a 45 deg swept airfoil. The pressure gradient is designed to provide purely crossflow-dominated transition; that is, the boundary layer is subcritical to Tollmien-Schlichting disturbances. The airfoil surface is hand polished to a 0.25 microns rms finish. Under these conditions, stationary crossflow disturbances grow to nonuniform amplitude due to submicron surface irregularities near the leading edge. Uniform stationary crossflow waves are produced by controlling the initial conditions with spanwise arrays of micron-sized roughness elements near the attachment line. Hot-wire measurements provide detailed maps of the crossflow wave structure, and accurate spectral decompositions isolate individual-mode growth rates for the fundamental and harmonic disturbances. Roughness spacing, roughness height, and Reynolds number are varied to investigate the growth of all amplified wavelengths. The measurements show early nonlinear mode interaction causing amplitude saturation well before transition. Comparisons with nonlinear parabolized stability equations calculations show excellent agreement in both the disturbance amplitude and the mode-shape profiles.

Saric, William S.↗
NASA NTRS1997

New Research by CCD Scanning for Comets and Asteroids

The purpose of Spacewatch is to explore the various populations of small objects within the solar system. Spacewatch provides data for studies of comets and asteroids, finds potential targets for space missions, and provides information on the environmental problem of possible impacts. Moving objects are discovered by scanning the sky with charge-coupled devices (CCDs) on the 0.9-meter Spacewatch Telescope of the University of Arizona on Kitt Peak. Each Spacewatch scan consists of three drift scan passes over an area of sky using a CCD filtered to a bandpass of 0.5-1.0 microns (approximately V+R+I with peak sensitivity at 0.7 micron). The effective exposure time for each pass is 143 seconds multiplied by the secant of the declination. We have been finding some 30,000 new asteroids per year and applying their statistics to the study of the collisional history of the solar system. As of the end of the observing run of Nov. 1997, Spacewatch had found a total of 153 Near-Earth Asteroids (NEAs) and 8 new comets since the project began in the 1980s, and had recovered one lost comet. The total number of NEAs found by Spacewatch big enough to be hazardous if they were to impact the Earth is 36. Spacewatch is also efficient in recovery of known comets and has detected and reported positions for more than 137,000 asteroids, mostly new ones in the main belt, including more than 16,000 asteroids designated by the Minor Planet Center (MPC).

Gehrels, Tom↗
NASA NTRS1998

Thermal and evolved gas analyzer

The Thermal and Evolved Gas Analyzer (TEGA) instrument will perform calorimetry and evolved gas analysis on soil samples collected from the Martian surface. TEGA is one of three instruments, along with a robotic arm, that form the Mars Volatile and Climate Survey (MVACS) payload. The other instruments are a stereo surface imager, built by Peter Smith of the University of Arizona and a meteorological station, built by JPL. The MVACS lander will investigate a Martian landing site at approximately 70 deg south latitude. Launch will take place from Kennedy Space Center in January, 1999. The TEGA project started in February, 1996. In the intervening 24 months, a flight instrument concept has been designed, prototyped, built as an engineering model and flight model, and tested. The instrument performs laboratory-quality differential-scanning calorimetry (DSC) over the temperature range of Mars ambient to 1400K. Low-temperature volatiles (water and carbon dioxide ices) and the carbonates will be analyzed in this temperature range. Carbonates melt and evolve carbon dioxide at temperatures above 600 C. Evolved oxygen (down to a concentration of 1 ppm) is detected, and C02 and water vapor and the isotopic variations of C02 and water vapor are detected and their concentrations measured. The isotopic composition provides important tests of the theory of solar system formation.

Williams, M. S.↗
NASA NTRS1997

Dynamic Reconstruction and Multivariable Control for Force-Actuated, Thin Facesheet Adaptive Optics

The Multiple Mirror Telescope (MMT) under development at the University of Arizona takes a new approach in adaptive optics placing a large (0.65 m) force-actuated, thin facesheet deformable mirror at the secondary of an astronomical telescope, thus reducing the effects of emissivity which are important in IR astronomy. However, The large size of the mirror and low stiffness actuators used drive the natural frequencies of the mirror down into the bandwidth of the atmospheric distortion. Conventional adaptive optics takes a quasi-static approach to controlling the, deformable mirror. However, flexibility within the control bandwidth calls for a new approach to adaptive optics. Dynamic influence functions are used to characterize the influence of each actuator on the surface of the deformable mirror. A linearized model of atmospheric distortion is combined with dynamic influence functions to produce a dynamic reconstructor. This dynamic reconstructor is recognized as an optimal control problem. Solving the optimal control problem for a system with hundreds of actuators and sensors is formidable. Exploiting the circularly symmetric geometry of the mirror, and a suitable model of atmospheric distortion, the control problem is divided into a number of smaller decoupled control problems using circulant matrix theory. A hierarchic control scheme which seeks to emulate the quasi-static control approach that is generally used in adaptive optics is compared to the proposed dynamic reconstruction technique. Although dynamic reconstruction requires somewhat more computational power to implement, it achieves better performance with less power usage, and is less sensitive than the hierarchic technique.

Grocott, Simon C. O.↗
NASA NTRS1994

ASU Formula Lightning Race Vehicle Report Prepared for Ohio Aerospace Institute

This report describes the drive system in the Arizona State University Formula Lightning electric race car when it participated in the 1994 Cleveland Electric Formula Classic on 9 July 1994. In addition, the telemetry system used to monitor the car's performance and plans for improving the car's performance are described.

Sirkis, Murray D.↗
NASA NTRS1998

A 2 THz Heterodyne Array Receiver for SOFIA

We proposed to perform a comprehensive design study of a 16-element heterodyne array receiver for SOFIA. The array was designed to utilize hot-electron bolometers in an efficient, low-cost waveguide mount to achieve low noise performance between approx. 1500 and 2400 GHz. Due to the prevailing physical conditions in the interstellar medium, this frequency range is one of the richest in the FIR portion of the spectrum. An array designed for this wavelength range will make excellent use of the telescope and the available atmospheric transmission, and will provide a new perspective on stellar, chemical, and galaxy evolution in the present as well as past epochs. A few of the most important molecular and atomic species which the instrument will sample are CII, OI, CO, OH, NII, and CH. The system used the most sensitive detectors available in an efficient optical system. The local oscillator was a compact CO2 pumped far-infrared laser currently under development for SOFIA. The backend spectrometer was an array acousto-optic spectrometer (aAOS). The spectrometer utilizes proven hardware and technologies to provide broadband performance (greater than or equal to 1 GHz per AOS channel) and high spectral resolution (1 MHz) with the maximum sensitivity and minimum complexity and cost. The proposed instrument would be the fastest and most sensitive heterodyne receiver ever to operate in the 1.5 - 2.4 THz band. One of the key technologies developed for the proposed instrument is the laser micromachining of waveguide structures. These structures provide both the optical link between the instrument and the telescope (via an array of efficient feedhorns) and the impedance transformation between the detectors and free space. With the assistance of funds provided from this grant, we were able to fabricate and test the world's first laser micromachined feedhorns. Figure 1 is a photograph of the 2 THz double feedhorn structure designed and constructed under the auspices of this grant. The quality of the waveguide structure is far better than that obtainable using any other fabrication technique. Figure 2 is the beam pattern obtained from it. The beam parameters are an excellent match to what is expected from theory. The success of this experiment demonstrates the viability of using laser micromachined components in the development of high performance, large format array receivers. Figure 3 is an illustration of the focal plane array concept we developed lot- SOFIA base upon this work. Un- fortunately, our instrument proposal was not selected as a first generation SOFIA instrument. However, we have continued our development efforts and will propose to build a 2nd generation instrument based on the same design concepts. Our work under NAG 2-1057 was very rewarding and we appreciate the opportunity provided by NASA to pursue it. The research led directly to publishing 2 papers (listed below) and the award of an NSF grant to our group to construct a laser micromachining system on the University of Arizona campus.

Walker, Christopher K.↗
NASA NTRS1999

Crossflow Stability and Transition Experiments in Swept-Wing Flow

An experimental examination of crossflow instability and transition on a 45deg swept wing was conducted in the Arizona State University Unsteady Wind Tunnel. The stationary-vortex pattern and transition location are visualized by using both sublimating chemical and liquid-crystal coatings. Extensive hot-wire measurements were obtained at several measurement stations across a single vortex track. The mean and travelling wave disturbances were measured simultaneously. Stationary crossflow disturbance profiles were determined by subtracting either a reference or a span-averaged velocity profile from the mean velocity data. Mean, stationary crossflow, and traveling wave velocity data were presented as local boundary layer profiles and contour plots across a single stationary crossflow vortex track. Disturbance mode profiles and growth rates were determined. The experimental data are compared with predictions from linear stability theory.

Dagenhart, J. Ray↗