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NASA NTRS1998

Transition and Breakdown to Turbulence in Incompressible Boundary Layers

We have developed a code where the nonlinear terms are treated implicitly. The equations are discretized using the two-point fourth order compact scheme in the y-direction and the backward Euler method in the x-direction. We investigated the transition process in a Blasius boundary layer due to fundamental type breakdown. With 8 modes in the w and 3 planes, we could compute the evolution of disturbances up to Re(x)=910, which is well into the strongly nonlinear region. The transition onset point is located around Re(x)=850. The comparison with the measurements and with the DNS computations are very good up to Re(x)=880.

Balakumar, Ponnampalam↗

NASA NTRS1996

Orbits Close to Asteroid 4769 Castalia

We use a radar-derived physical model of 4769 Castalia (1989 PB) to investigate close orbit dynamics around that kilometer- sized, uniformly rotating asteroid. Our methods of analysis provide a basis for systematic studies of particle dynamics close to any uniformly rotating asteroid. We establish that a Jacobi integral exists for particles orbiting this asteroid, examine the attendant zero-velocity surfaces, find families of periodic orbits, and determine their stability. All synchronous orbits and direct orbits within approx. 3 mean radii of Castalia are unstable and are subject to impact or escape from Castalia. Retrograde orbits are mostly stable and allow particles to orbit close to the asteroid surface. We derive a model which allows us to predict the escape conditions of a particle in orbit about Castalia and the (temporary) capture conditions for a hyperbolic interloper. Orbits within 1.5 km of Castalia are subject to immediate ejection from the system. Hyperbolic orbits with a V(sub infinity) less than 0.4 m/sec can potentially be captured by Castalia if their periapsis radius Is within approx. 2 km. For Castalia this capture region is small, but the results also apply to larger asteroids whose capture regions would also be larger. We determine bounds on ejecta speeds which either ensure ejecta escape or re-impact as functions of location on Castalia's surface. The speeds that ensure escape range from 0.28 to 0.84 m/sec and the speeds that ensure re-impact range from 0 to 0.18 m/sec. Speeds between these two bounds lead either to escape, re-impact, or potentially finite-time stable orbits. We develop a simple criterion which can establish whether a particle could have been ejected from the asteroid in the past and if it will impact the surface in the future.

Scheeres, D. J.↗

NASA NTRS1976

Effect of Propranolol on Thyroxine-Induced Changes in Body Temperature and Metabolism During Exercise in Dogs

Effects of thyroxine on temperature and metabolism during exercise were studied in dogs after beta-adrenergic blockade. Dogs performed 60 min treadmill exercise of moderate intensity 5 and 72 h following thyroxine injected s. c. in a single dose of 0.1 mg/kg b.w. Thyroxine increased significantly the lipolytic response to exercise as well as blood lactate (LA) concentrations and rectal temperature (T(sub re)) during exercise as early as 5 h following the hormone administration. The changes became more pronounced 72 h after the injection. At rest T(sub re), blood FFA (free fatty acid) and LA levels in the thyroxine-treated dogs did not differ from the control values, and blood glucose was slightly, but significantly higher. Propranolol given intravenously in a dose of 0.25 mg/kg at 30 min of the exercise performed 72 h following thyroxine injection abolished the plasma FFA rise, and inhibited to a certain extent increases in T(sub re) and blood LA concentrations during the next 30 min of exercise.

Kaciuba-Uscilko, Hanna↗

NASA NTRS1998

Magnetospheric Response to the Arrival of the Shock Wave in Front of the Magnetic Cloud Event of January 10,1997

We are studying the magnetic cloud event of January 6-11, 1997. Specifically, we have investigated the response of the magnetosphere to the shock wave in front of the magnetic cloud on January 10, 1997 using data from WIND, GEOTAIL and POLAR spacecraft as well as ground magnetometer data. The WIND spacecraft, which was located at about 100 Re upstream from the Earth, observed the arrival of the shock wave front at 005OUT. Geotail was located at the equatorial magnetopause (approx. 8.7 Re), while POLAR was located in the northern dawn sector at 8.4 Re, 6.1 MLT and 61.1 MLAT. A magnetic signature was nearly simultaneously observed at about 0104 UT at the POLAR and Geotail spacecraft. Particle density increases were observed on WIND and Geotail, but not on POLAR. The UV aurora shows an asymmetrical dawn-dusk intensification and presubstorm activity. The significance of these findings will be discussed.

Wuest, M.↗

NASA NTRS1998

A Study of Ion Velocities Observed by TIDE and How It Relates to Magnetospheric Circulation

The high-latitude ion velocities measured by the Thermal Ion Dynamics Experiment (TIDE) instrument on the Polar spacecraft will be examined in relation to magnetospheric circulation. TIDE derives ion velocities from moments of measured distribution functions. Hydrogen and oxygen ions are E X B drifting in the polar cap and cleft regions with a speed of about 5-20 km/s at apogee (approximately 9 Re) and a speed of 1-2 km/s at perigee (approximately 1.8 Re). At perigee 0+ is typically seen flowing down in the polar cap and outflowing from the cleft. At the transition from downflowing to upflowing there is also seen a reversal in the ion convection. The convection at perigee is consistent with standard ionospheric convection models for given Interplanetary Magnetic Field (IMF) conditions. Convection at high altitude (approximately 8.9 Re) polar regions has not been studied very much since there have not been many satellites in this region. Unlike previous missions to this region TIDE in conjunction the Plasma Source Instrument (PSI) can measure ions with as low an energy as several electron Volts. The outflowing ions observed by TIDE at apogee are believed to be important to the overall circulation of the magnetosphere. The convection of these outflowing ions at apogee will be related to the IMF. This study tries to answer the question of how the IMF response of the convection influences the overall circulation of the magnetosphere.

Elliott, H. A.↗

NASA NTRS1995

Laboratory Investigation of Direct Measurement of Ice Water Content, Ice Surface Area, and Effective Radius of Ice Crystals Using a Laser-Diffraction Instrument

The aircraft microphysics probe, PVM-100A, was tested in the Colorado State University dynamic cloud chamber to establish its ability to measure ice water content (IWC), PSA, and Re in ice clouds. Its response was compared to other means of measuring those ice-cloud parameters that included using FSSP-100 and 230-X 1-D optical probes for ice-crystal concentrations, a film-loop microscope for ice-crystal habits and dimensions, and an in-situ microscope for determining ice-crystal orientation. Intercomparisons were made in ice clouds containing ice crystals ranging in size from about 10 microns to 150 microns diameter, and ice crystals with plate, columnar, dendritic, and spherical shapes. It was not possible to determine conclusively that the PVM accurately measures IWC, PSA, and Re of ice crystals, because heat from the PVM evaporated in part the crystals in its vicinity in the chamber thus affecting its measurements. Similarities in the operating principle of the FSSP and PVM, and a comparison between Re measured by both instruments, suggest, however, that the PVM can make those measurements. The resolution limit of the PVM for IWC measurements was found to be on the order of 0.001 g/cubic m. Algorithms for correcting IWC measured by FSSP and PVM were developed.

Gerber, H.↗

NASA NTRS1999

Integrating Thermal Tools Into the Mechanical Design Process

The intent of mechanical design is to deliver a hardware product that meets or exceeds customer expectations, while reducing cycle time and cost. To this end, an integrated mechanical design process enables the idea of parallel development (concurrent engineering). This represents a shift from the traditional mechanical design process. With such a concurrent process, there are significant issues that have to be identified and addressed before re-engineering the mechanical design process to facilitate concurrent engineering. These issues also assist in the integration and re-engineering of the thermal design sub-process since it resides within the entire mechanical design process. With these issues in mind, a thermal design sub-process can be re-defined in a manner that has a higher probability of acceptance, thus enabling an integrated mechanical design process. However, the actual implementation is not always problem-free. Experience in applying the thermal design sub-process to actual situations provides the evidence for improvement, but more importantly, for judging the viability and feasibility of the sub-process.

Tsuyuki, Glenn T.↗

NASA NTRS1999

Temperature Compensated Sapphire Resonator for Ultrastable Oscillator Operating at Temperatures Near 77 Deg Kelvin

A sapphire resonator for an ultrastable oscillator capable of substantial performance improvements over the best available crystal quartz oscillators in a compact cryogenic package is based on a compensation mechanism enabled by the difference between copper and sapphire thermal expansion coefficients for so tuning the resonator as to cancel the temperature variation of the sapphire's dielectric constant. The sapphire resonator consists of a sapphire ring separated into two parts with webs on the outer end of each to form two re-entrant parts which are separated by a copper post. The re-entrant parts are bonded to the post by indium solder for good thermal conductivity between parts of that subassembly which is supported on the base plate of a closed copper cylinder (rf shielding casing) by a thin stainless steel cylinder. A unit for temperature control is placed in the stainless steel cylinder and is connected to the subassembly of re-entrant parts and copper post by a layer of indium for good thermal conduction. In normal use, the rf shielding casing is placed in a vacuum tank which is in turn placed in a thermos flask of liquid nitrogen. The temperature regulator is controlled from outside the thermos flask to a temperature in a range of about 40K to 150K, such as 87K for the WGH-811, mode of resonance in response to microwave energy inserted into the rf shielding casing through a port from an outside source.

Dick, G. John↗

NASA NTRS2000

Measurements in Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions

Detailed velocity measurements were made along a flat plate subject to the same dimensionless pressure gradient as the suction side of a modern low-pressure turbine airfoil. Reynolds numbers based on wetted plate length and nominal exit velocity were varied from 50,000 to 300,000, covering cruise to takeoff conditions. Low and high inlet free-stream turbulence intensities (0.2% and 7%) were set using passive grids. The location of boundary-layer separation does not depend strongly on the free-stream turbulence level or Reynolds number, as long as the boundary layer remains non-turbulent prior to separation. Strong acceleration prevents transition on the upstream part of the plate in all cases. Both free-stream turbulence and Reynolds number have strong effects on transition in the adverse pressure gradient region. Under low free-stream turbulence conditions transition is induced by instability waves in the shear layer of the separation bubble. Reattachment generally occurs at the transition start. At Re = 50,000 the separation bubble does not close before the trailing edge of the modeled airfoil. At higher Re, transition moves upstream, and the boundary layer reattaches. With high free-stream turbulence levels, transition appears to occur in a bypass mode, similar to that in attached boundary layers. Transition moves upstream, resulting in shorter separation regions. At Re above 200,000, transition begins before separation. Mean velocity, turbulence and intermittency profiles are presented.

Volino, Ralph J.↗

NASA NTRS1993

Mars Observer Press Conference JPL

The Mars Observer mission spacecraft was primarily designed for exploring Mars and the Martian environment. The Mars Observer was launched on September 25, 1992. The spacecraft was lost in the vicinity of Mars on August 21, 1993 when the spacecraft began its maneuvering sequence for Martian orbital insertion. This videotape shows a press briefing, held after the spacecraft had not responded to attempts to communicate with it, to explain to the press the problems and the steps that were being taken to re-establish communication with the spacecraft. The communications had been shutdown prior to the orbital insertion burn to protect the instruments. At the time of the press conference, the communications system was still not operational, and attempts were being made to re-establish communication. Bob McMillan of the Public Affairs Office at JPL gives the initial announcement of the continuing communication problem with the spacecraft. Mr. McMillan introduces William Piotrowski, acting director of solar system exploration, who reiterates that there is indeed no communication with the Observer spacecraft. He is followed by Glenn Cunningham, the Project Manager of the Mars Observer who speaks about the attempts to re-establish contact. Mr. Cunningham is followed by Satenios Dallas, the Mission Manager for the Mars Observer Project, who speaks about the sequence of events leading up to the communication failure, and shows an animated video presenting the orbital insertion maneuvers. The briefing was then opened up for questions from the assembled press, both at JPL and at the other NASA Centers. The questions are about the possible reasons for the communication failure, and the attempts to restore communications with the spacecraft. Dr. Arden L. Albee, chief scientist for the Mars Observer Mission, joins the other panel members to answer questions. At the end of the press briefing the animation of the Mars orbital insertion is shown again.

Source record↗

NASA NTRS1999

CRV Escape Trajectories from the ISS

The Crew Return Vehicle (CRV) slated for use on the International Space Station (ISS) provides a safe return for up to seven crew members under various emergency conditions. One of the most demanding situations for executing the escape involves separating from a tumbling ISS Current requirements specify a maximum Root Sum Square (RSS) tumble rate of 2 degrees/second, with the additional requirement for an expedited departure from any ISS attitude. The design of a trajectory that ensures no re-contact with the ISS poses many challenges on the Guidance, Navigation, and Control (GN&C) system of the vehicle. To ensure no re-contact the trajectory design employs a two burn sequence, with the first burn preventing near-term collision and the second burn preventing far-field re-contact This presentation describes the approach used to design and to evaluate trajectories for CRV departure from the baselined location on the ISS Node 3 starboard. This approach involved performing a parametric search of selected control variables vital in escaping the tumbling ISS The presentation provides a candidate targeting methodology for escape using minimal information from available navigation devices, and presents the quantitative results from the analysis.

Foti, Tony M.↗

NASA NTRS1999

Buoyancy Driven Shear Flows of Bubble Suspensions

In this work the gas volume fraction and the root-mean-squared fluid velocity are measured in buoyancy driven shear flows of bubble suspensions in a tall, inclined, rectangular channel. The experiments are performed under conditions where We << 1a nd Re >> 1, for which comparisons are made with kinetic theory and numerical simulations. Here Re = gamma(a(exp 2)/nu is the Reynolds number and We = rho(gamma(exp 2))a(exp 3)/sigma is the Weber number; gamma is the shear rate, a is the bubble radius, nu is the kinematic viscosity of the liquid, rho is the density of the liquid, and sigma is the surface tension of the gas/liquid interface. Kang et al. calculated the bubble phase pressure and velocity variance of sheared bubble suspensions under conditions where the bubbles are spherical and the liquid phase velocity field can be approximated using potential flow theory, i.e. We= 0 and Re >> 1. Such conditions can be achieved in an experiment using gas bubbles, with a radius of O(0.5mm), in water. The theory requires that there be no average relative motion of the gas and liquid phases, hence the motivation for an experimental program in microgravity. The necessity of performing preliminary, Earth based experiments, however, requires performing experiments where the gas phase rises in the liquid, which significantly complicates the comparison of experiments with theory. Rather than comparing experimental results with theory for a uniform, homogeneous shear flow, experiments can be compared directly with solutions of the averaged equations of motion for bubble suspensions. This requires accounting for the significant lift force acting on the gas phase when the bubbles rise parallel to the average velocity of the sheared suspension. Shear flows can be produced in which the bubble phase pressure gradient, arising from shear induced collisions amongst the bubbles, balances a body force (centrifugal or gravitational) on the gas phase. A steady, non-uniform gas volume fraction can be measured, from which the bubble phase pressure gradient can be obtained and compared to theory and numerical simulations. The presence of bounding walls further complicates the experiments, since the detailed interactions of the bubbles with bounding walls is not well understood, especially in the presence of gravity, where the momentum and energy exchange depends on the inclination of the wall.

Koch, D. L.↗

NASA NTRS2000

Renewable Energy SCADA/Training Using NASA's Advanced Technology Communication Satellite

The lack of electrical energy in the rural communities of developing countries is well known, as is the economic unfeasibility of providing much needed energy to these regions via electric grids. Renewable energy (RE) can provide an economic advantage over conventional forms in meeting some of these energy needs. The use of a Supervisory Control and Data Acquisition (SCADA) arrangement via satellite could enable experts at remote locations to provide technical assistance to local trainees while they acquire a measure of proficiency with a newly installed RE system through hands-on training programs using the same communications link. Upon full mastery of the technologies, indigenous personnel could also employ similar SCADA arrangements to remotely monitor and control their constellation of RE systems. Two separate ACTS technology verification experiments (TVEs) have demonstrated that the portability of the Ultra Small Aperture Terminal (USAT) and the versatility of NASA's Advanced Communications Technology Satellite (ACTS), as well as the advantages of Ka band satellites, can be invaluable in providing energy training via distance education (DE), and for implementing renewable energy system SCADA. What has not been tested is the capabilities of these technologies for a simultaneous implementation of renewable energy DE and SCADA. Such concurrent implementations will be useful for preparing trainees in developing countries for their eventual SCADA operations. The project described in this correspondence is the first effort, to our knowledge, in this specific TVE. The setup for this experiment consists of a one-Watt USAT located at Florida Solar Energy Center (FSEC) connected to two satellite modems tuned to different frequencies to establish two duplex ACTS Ka-band communication channels. A short training program on operation and maintenance of the system will be delivered while simultaneously monitoring and controlling the hybrid using the same satellite communications link. The trainees will include faculty and students from Savannah State University, and staff from FSEC. An interactive internet link will be used to allow faculty from the University of West Indies to participate in the training session.

Kalu, A.↗

NASA NTRS2000

Towards LES Models of Jets and Plumes

As pointed out by Rodi standard integral solutions for jets and plumes developed for discharge into infinite, quiescent ambient are difficult to extend to complex situations, particularly in the presence of boundaries such as the sea floor or ocean surface. In such cases the assumption of similarity breaks down and it is impossible to find a suitable entrainment coefficient. The models are also incapable of describing any but the most slowly varying unsteady motions. There is therefore a need for full time-dependent modeling of the flow field for which there are three main approaches: (1) Reynolds averaged numerical simulation (RANS), (2) large eddy simulation (LES), and (3) direct numerical simulation (DNS). Rodi applied RANS modeling to both jets and plumes with considerable success, the test being a match with experimental data for time-averaged velocity and temperature profiles as well as turbulent kinetic energy and rms axial turbulent velocity fluctuations. This model still relies on empirical constants, some eleven in the case of the buoyant jet, and so would not be applicable to a partly laminar plume, may have limited use in the presence of boundaries, and would also be unsuitable if one is after details of the unsteady component of the flow (the turbulent eddies). At the other end of the scale DNS modeling includes all motions down to the viscous scales. Boersma et al. have built such a model for the non-buoyant case which also compares well with measured data for mean and turbulent velocity components. The model demonstrates its versatility by application to a laminar flow case. As its name implies, DNS directly models the Navier-Stokes equations without recourse to subgrid modeling so for flows with a broad spectrum of motions (high Re) the cost can be prohibitive - the number of required grid points scaling with Re(exp 9/4) and the number of time steps with Re(exp 3/4). The middle road is provided by LES whereby the Navier-Stokes equations are formally filtered with the filter chosen to only exclude the smallest turbulent motions. If successful, LES should provide much of the detail available to DNS but at more bearable cost. Fatica et al. in comparing LES with DNS for a low Reynolds number jet showed that the LES could simulate the temporally evolving behavior including growth of the jet thickness. It is the intention of this report to explore the application of an LES model to jets and plumes. As always, before tackling complex situations, the model must be tested for the simplest of cases and so we address only two, a non-buoyant axisymmetric jet issuing steadily from an orifice into a semi-infinite stationary environment and a buoyant jet in the same environment. The work is a continuation of Basu and Mansour.

Webb, A. T.↗

NASA NTRS2001

Characterization of Rhenium Oxides Using ESCA

High melting point and inherent ductility (toughness) over a wide range of temperature has made Rhenium an engineering material of choice for several thrust chambers in propulsion systems. Although the material remains tough at high temperatures, it still can readily transform to several oxides. As many as eight different oxides have been reported in literature. When characterized using ESCA (Electron Spectroscopy for Chemical Analyses) these oxides show large shifts in the Re 4f line positions. While this unique property could be used as a tool for oxide characterization, literature indicates that only a few of these oxides have been characterized. Current work focuses on characterizing oxides of Rhenium using ESCA. Spectral line Re 4f have been measured for various oxides and the results have been compared with the Re 4f line positions of real-time oxidation products from space hardware.

Panda, Binayak↗

NASA NTRS2001

A Long-Term Space Astrophysics Research Program: The Evolution of the Quasar Continuum

Four papers have been written. One reports on the major study funded by this grant: a pan-chromatic study of the quasar continuum at redshift 3. Two others make use of the quasar continuum shapes to find the minimum total accretion luminosity of the Universe, and hence the efficiency and spin of supermassive black holes; the second shows that the reemission of absorbed quasar radiation alleviates a major problem with galaxy formation and the FIR background. The last paper recognizes the role quasars may play in the initial formation of dust in the early Universe. The major study of a sample of z=3 and its comparison with a sample of z=0.l quasars across the whole X-ray to radio spectrum was completed and accepted for publication in ApJ Supplements. This study comprises the thesis work of Olga Kuhn. The two samples are matched in evolved luminosity, and so should be sampling the same black hole population at different z, and in different accretion states. Despite this no strong differences were found between the samples, except in the 'small bump' region of the optical/UV. This region is dominated by FeII emission, and may indicate abundance evolution in quasars. The lack of overall spectral changes argues strongly against a single population of quasars fading over cosmic time, and for a multiple generation, or multiple outburst model for quasars. A study of the total luminosity absorbed from quasars and re-emitted in the infrared produced two results (reported in two papers): The minimum intrinsic luminosity/Gpc(3) from AGN compared with the measured mass density in supermassive black holes [Gpc(-3)] requires a conversion efficiency of accreted mass into luminosity of greater than 15%. Non-rotating black holes cannot exceed 5% efficiency, while rapidly rotating black holes can reach 47%. Hence our result requires that most supermassive black holes must be rapidly rotating. The second result comes from considering the contribution that the re-radiated quasar radiation makes to the far infrared background (FIRB). The effective temperature of the re radiation is tightly constrained, but the detailed shape (e.g. line emission, range of temperature) is only of second order importance. At least 15perhaps 20-25% of the FIR background must come from AGN. This contribution significantly relieves problems in galaxy evolution that come from trying to use only starlight to make the FIRB. The third paper addresses the origin of the dust obscuration that is so widespread in AGN. The standard assumption is that the dust comes from the normal star-formation processes in galaxies and is drawn close to the nucleus along with the gas that powers the accretion. In complete contrast, using a wind outflow model for the broad emission line (BEL) region (Elvis 2000) as a basis, we show that BEL clouds will expand, cool and form dust as they flow outward, in strict analogy to the stellar winds of red supergiants.

Elvis, M.↗

NASA NTRS1995

The Evolution of Plane Wakes Subjected to Irrotational Strains

Three direct numerical simulations of time-evolving turbulent plane wakes developing in the presence of various irrotational plane strains have been generated. A pseudospectral numerical method with up to 26 million modes is used to solve the equations in a reference frame moving with the irrotational strain. The initial condition for each simulation is taken from a previous turbulent self-similar plane wake direct numerical simulation at a velocity deficit Reynolds number, Re, of about 2000. Three different plane strains (of the same magnitude) are imposed. In the first two simulations the strain is in a plane normal to the streamwise wake direction (the two cases having strain of opposite sign); in the third the wake is compressed in the streamwise direction and stretched in the inhomogeneous cross-stream direction. The two flows that are stretched in the cross-stream direction experience an exponential increase of Re; flow visualization indicates many small-scale vortices with little or no organized large-scale structure. In the flow that is compressed in the cross-stream direction Re decays exponentially and the layer appears to be relaminarizing. The evolution of several turbulence statistics in each of these flows is examined.

Rogers, M. R.↗

NASA NTRS2002

D-Wave Resonances in Positronium Hydride

The problem of calculating the position and width of the lowest-lying (L = 0, 1) resonances in the Ps + H scattering system has recently been re-examined by the authors [1]. In the model used, resonances axe assumed generated by bound Rydberg states in the closed re-arranged channel [e(+) + H(-)]. This infinite series of Coulomb bound states are shifted somewhat by the coupling with the open scattering channel [Ps + H]. Estimates using this approach, first carried out by one of the authors [2] using a simple form of scattering wavefunction, indicated an anticipated small shift of resonance away from the Rydberg energy in the S-wave (L = 0). More recent results by Ho and Yan [3] using the complex-rotation method showed unexpected significant shifting in the P (L = 1) and D (L = 2)-wave resonance energies from their respective unperturbed values. Our re-calculation of the resonances [I I for L = 0 and I indicates that, in each case, reasonably consistent resonance energies are obtained by coupling the two lowest lying states (IS and 2S for L = 0 and 2P and 3P for L = 1). For each L it is the higher state (2S and 3P, respectively) that produces the resonance. The lower state (1S and 2P, respectively) is effective only in increasing the non-resonant phase shift. In this work we extend the model to L = 2 (D-waves). Our results show that, unlike the S and P-waves, the 313-state alone produces a resonant energy that is very close to the result of Yan and Ho [3]. Inclusion of the 4D-state produces a second resonance in the scattering system shifted up slightly from its unperturbed Rydberg energy.

Drachman, Richard J.↗