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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Backward-facing step measurements at low Reynolds number, Re(sub h)=5000

An experimental study of the flow over a backward-facing step at low Reynolds number was performed for the purpose of validating a direct numerical simulation (DNS) which was performed by the Stanford/NASA Center for Turbulence Research. Previous experimental data on back step flows were conducted at Reynolds numbers and/or expansion ratios which were significantly different from that of the DNS. The geometry of the experiment and the simulation were duplicated precisely, in an effort to perform a rigorous validation of the DNS. The Reynolds number used in the DNS was Re(sub h)=5100 based on step height, h. This was the maximum possible Reynolds number that could be economically simulated. The boundary layer thickness, d, was approximately 1.0 h in the simulation and the expansion ratio was 1.2. The Reynolds number based on the momentum thickness, Re(sub theta), upstream of the step was 610. All of these parameters were matched experimentally. Experimental results are presented in the form of tables, graphs and a floppy disk (for easy access to the data). An LDV instrument was used to measure mean velocity components and three Reynolds stresses components. In addition, surface pressure and skin friction coefficients were measured. LDV measurements were acquired in a measuring domain which included the recirculating flow region.

Jovic, Srba↗
NASA NTRS1994

Re-engineering the mission life cycle with ABC and IDEF

The theory behind re-engineering a business process is to remove the non-value added activities thereby lowering the process cost. In order to achieve this, one must be able to identify where the non-value added elements are located which is not a trivial task. This is because the non-value added elements are often hidden in the form of overhead and/or pooled resources. In order to be able to isolate these non-value added processes from among the other processes, one must first decompose the overall top level process into lower layers of sub-processes. In addition, costing data must be assigned to each sub-process along with the value the sub-process adds towards the final product. IDEF0 is a Federal Information Processing Standard (FIPS) process-modeling tool that allows for this functional decomposition through structured analysis. In addition, it illustrates the relationship of the process and the value added to the product or service. The value added portion is further defined in IDEF1X which is an entity relationship diagramming tool. The entity relationship model is the blueprint of the product as it moves along the 'assembly line' and therefore relates all of the parts to each other and the final product. It also relates the parts to the tools that produce the product and all of the paper work that is used in their acquisition. The use of IDEF therefore facilitates the use of Activity Based Costing (ABC). ABC is an essential method in a high variety, product-customizing environment, to facilitate rapid response to externally caused change. This paper describes the work being done in the Mission Operations Division to re-engineer the development and operation life cycle of Mission Operations Centers using these tools.

Mandl, Daniel↗
NASA NTRS1995

Asymmetric mass accretion in the magnetic cataclysmic variable RE 1149 + 28

We present the first detailed extreme photometric observations of a magnetic cataclysmic variable. Our two Extreme Ultraviolet Explorer (EUVE) observations of the AM Her star RE 1149 + 28 were obtained about 1 yr apart and show light-curve variations on orbital to yearly timescales, as well as long-term mean flux level changes of a factor of 2. The photometric data show a persistent ingress EUV enhancement which lasts approximately 0.04 in phase. We attribute this to a region of approximately 10(exp 3) km in extent at the accretion impact site, on or very near the surface of the white dwarf primary. Our observations of RE 1149 are consistent with a relatively low system inclination and provide a best-fit orbital period of 90.14 +/- 0.015 minutes.

Howell, Steve B.↗
NASA NTRS1995

A spatially adaptive spectral re-ordering technique for lossless coding of hyper-spectral images

In this paper, we propose a new approach, applicable to lossless compression of hyper-spectral images, that alleviates some limitations of linear prediction as applied to this problem. According to this approach, an adaptive re-ordering of the spectral components of each pixel is performed prior to prediction and encoding. This re-ordering adaptively exploits, on a pixel-by pixel basis, the presence of inter-band correlations for prediction. Furthermore, the proposed approach takes advantage of spatial correlations, and does not introduce any coding overhead to transmit the order of the spectral bands. This is accomplished by using the assumption that two spatially adjacent pixels are expected to have similar spectral relationships. We thus have a simple technique to exploit spectral and spatial correlations in hyper-spectral data sets, leading to compression performance improvements as compared to our previously reported techniques for lossless compression. We also look at some simple error modeling techniques for further exploiting any structure that remains in the prediction residuals prior to entropy coding.

Memon, Nasir D.↗
NASA NTRS1996

An Experimental Study of a Separated/Reattached Flow Behind a Backward-Facing Step. Re(sub h) = 37,000

An experimental study was carried out to investigate turbulent structure of a two-dimensional incompressible separating/reattaching boundary layer behind a backward-facing step. Hot-wire measurement technique was used to measure three Reynolds stresses and higher-order mean products of velocity fluctuations. The Reynolds number, Re(sub h), based on the step height, h, and the reference velocity, U(sub 0), was 37,000. The upstream oncoming flow was fully developed turbulent boundary layer with the Re(sub theta) = 3600. All turbulent properties, such as Reynolds stresses, increase dramatically downstream of the step within an internally developing mixing layer. Distributions of dimensionless mean velocity, turbulent quantities and antisymmetric distribution of triple velocity products in the separated free shear layer suggest that the shear layer above the recirculating region strongly resembles free-shear mixing layer structure. In the reattachment region close to the wall, turbulent diffusion term balances the rate of dissipation since advection and production terms appear to be negligibly small. Further downstream, production and dissipation begin to dominate other transport processes near the wall indicating the growth of an internal turbulent boundary layer. In the outer region, however, the flow still has a memory of the upstream disturbance even at the last measuring station of 51 step-heights. The data show that the structure of the inner layer recovers at a much faster rate than the outer layer structure. The inner layer structure resembles the near-wall structure of a plane zero pressure-gradient turbulent boundary layer (plane TBL) by 25h to 30h, while the outer layer structure takes presumably over 100h.

Jovic, Srba↗
NASA NTRS1996

Minimum Heating Re-Entry Trajectories for Advanced Hypersonic Launch Vehicles

Optimal re-entry trajectories are generated for reusable launch vehicles which minimize: (1) the heat absorbed at the vehicle surface, (2) the lower surface temperature, and (3) the heat absorbed by the internal structure. The approach uses the energy state approximation technique and a finite control volume heat transfer code coupled to a flight path integration code. These trajectories are compared to the optimal re-entry trajectory minimizing the integrated convective heat rate to determine which trajectory produces the minimum internal structural temperatures for a given thermal protection system. Three different thermal protection systems are considered: tile, blanket, and metallic.

Robert Windhorst↗
NASA NTRS1997

Near-Optimal Re-Entry Trajectories for Reusable Launch Vehicles

A near-optimal guidance law for the descent trajectory for earth orbit re-entry of a fully reusable single-stage-to-orbit pure rocket launch vehicle is derived. A methodology is developed to investigate using both bank angle and altitude as control variables and selecting parameters that maximize various performance functions. The method is based on the energy-state model of the aircraft equations of motion. The major task of this paper is to obtain optimal re-entry trajectories under a variety of performance goals: minimum time, minimum surface temperature, minimum heating, and maximum heading change; four classes of trajectories were investigated: no banking, optimal left turn banking, optimal right turn banking, and optimal bank chattering. The cost function is in general a weighted sum of all performance goals. In particular, the trade-off between minimizing heat load into the vehicle and maximizing cross range distance is investigated. The results show that the optimization methodology can be used to derive a wide variety of near-optimal trajectories.

Chou, H.-C.↗
NASA NTRS1997

Oxidation and Emittance Studies of Coated Mo-Re

A commercially available Fe-Cr-Si coating (R512E) and a silicide coating were evaluated regarding their ability to protect Mo-Re from oxidation. The R512E coating provided very good oxidation protection at 1260 C in atmospheric air. Oxidation tests were also performed at Mach 4 in the HYMETS facility at NASA Langley Research Center where again the R512E provided good oxidation protection but for much shorter times. Emittance measurements as a function of wavelength were also obtained for the R512E coating on Mo-Re after exposure to the Mach 4 environment at 1150 C and 1230 C.

Glass, David E.↗
NASA NTRS1997

Polar Wind in the Context of the Auroral Plasma Fountain for 2 to 8 RE

Operations of the POLAR Plasma Source Instrument have provided adequate observing time with controlled spacecraft potential to begin a 3D characterization of the polar wind as it exists in the context of the auroral plasma fountain. The principal periods of such polar wind observation to date have been 15-18 Apr. 96, 28 may 96, 14 Jun. - 6 Sep. 96, 17-29 Mar. 97, 29 May - 12 Jun. 97, 13-27 Aug. 97. Separate observations have been made near 2 RE geocentric in the south polar perigee passes and between 6-8 RE geocentric in the north polar apogee passes. Analyses of data from the Thermal Ion Dynamics Experiment during these periods are used to characterize the altitude, local time, and invariant latitude distribution of the polar wind. Data from these and other periods are used to establish the auroral plasma heating context within which the polar wind outflows exist. The available data will be used to address the temporal variability of the polar wind during the period of operations to date. Comparisons between the observations and a coupled fluid-semikinetic model are used to interpret the observed spatial structure and temporal variability.

Moore, T. E.↗
NASA NTRS1998

Re-examination of a Classic Experiment to Measure the Positronium-Helium Cross Section

In 1975, before the advent of positronium beams, a clever experiment was carried out in an attempt to measure low-energy Ps-atom scattering cross-sections, especially that of Ps-He. A series of parallel thin plates was placed in the vessel containing the sample of gas, and positrons were allowed to enter the chamber from a radioactive source. The time spectrum of annihilation radiation was observed in the traditional way, and the pickoff annihilation due to thermalized Ps striking one of the plates was to be the special feature of the experiment. Using a diffusion analysis the authors derived cross- sections for several gases, and for helium the value obtained was sigma = 0.0166 pi(alpha)(sub o, sup 2). Even then this value was thought to be very much too small, while recent measurements and some calculations suggest a more reasonable value would be sigma = 3 to 13 pi(alpha)(sub o,sup 2). It has always been puzzling that an apparently well-designed experiment should give such an unsatisfactory result. We have now re-examined the analysis of the data with some interesting consequences which may explain the discrepancy. Two main observations support our re-analysis. First, we note that the mean free path for Ps-He scattering would be quite long if the cross-section were as small as that quoted above; the diffusion method itself would seem to be questionable. For the larger values, however, there would be no such problem. Second, it was assumed that when the annihilation rate had settled down and was following an exponential decay curve the asymptotic solution of the diffusion equation had been reached. We find, instead, that a superposition of exponentials can accurately represent the decay curve, consistent with the higher cross-section value.

Drachman, Richard J.↗
NASA NTRS2000

NASA Master Teacher Re-Certification Program

Edward Waters College is submitting a final report covering the grant period from January 1999 - April 30, 2000. The Teacher re-certification program at Edward Waters College created a high quality professional development opportunity for middle and high school science teachers which will contribute to the improvement of science education and the use of innovation technologies in the classroom for years to come. The following goals and objectives were met and exceeded during the grant period. 1) A focused and relevant educational technology curriculum based on National Science Education Standard and state-of-the art educational resources that are accepted as one of the qualifications for re-certification in the scientific discipline in Duval County, Florida. 2) The program goal was to recertify 40 middle and high school science teachers over a two- year period. This goal was met and exceeded the projected number by recertifying over 80 middle and high school science and math teachers over a two-year period. 3) Teachers that were recertified were given an opportunity to public information that they developed on EWC's Web page or develop a web page of their own. Area schools were made aware of this information through various forms of communication with the teachers in Duval County School District, i.e., flyers sent from EWC to participants, school newspapers, word of mouth, etc. 4) A multimedia technology resource lab is available at EWC for use as a "Learning Lab" for class field trips by Duval County teachers.

Okari-Brooks, Emma↗
NASA NTRS2001

Thermal Analysis and Design of Multi-layer Insulation for Re-entry Aerodynamic Heating

The combined radiation/conduction heat transfer in high-temperature multi-layer insulations was modeled using a finite volume numerical model. The numerical model was validated by comparison with steady-state effective thermal conductivity measurements, and by transient thermal tests simulating re-entry aerodynamic heating conditions. A design of experiments technique was used to investigate optimum design of multi-layer insulations for re-entry aerodynamic heating. It was found that use of 2 mm foil spacing and locating the foils near the hot boundary with the top foil 2 mm away from the hot boundary resulted in the most effective insulation design. A 76.2 mm thick multi-layer insulation using 1, 4, or 16 foils resulted in 2.9, 7.2, or 22.2 percent mass per unit area savings compared to a fibrous insulation sample at the same thickness, respectively.

Daryabeigi, Kamran↗
NASA NTRS2001

Further Investigations of Control Surface Seals for the X-38 Re-Entry Vehicle

NASA is currently developing the X-38 vehicle that will be used to demonstrate the technologies required for a potential crew return vehicle (CRV) for the International Space Station. This vehicle would serve both as an ambulance for medical emergencies and as an evacuation vehicle for the Space Station. Control surfaces on the X-38 (body flaps and rudder/fin assemblies) require high temperature seals to limit hot gas ingestion and transfer of heat to underlying low-temperature structures to prevent over-temperature of these structures and possible loss of the vehicle. NASAs Johnson Space Center (JSC) and Glenn Research Center (GRC) are working together to develop and evaluate seals for these control surfaces. This paper presents results for compression. flow, scrub, and arc jet tests conducted on the baseline X-38 rudder/fin seal design. Room temperature seal compression tests were performed at low compression levels to determine load versus linear compression, preload. contact area, stiffness. and resiliency characteristics under low load conditions. For all compression levels that were tested, unit loads and contact pressures for the seals were below the 5 lb/in. and 10 psi limits required to limit the loads on the adjoining Shuttle thermal tiles that the seals will contact. Flow rates through an unloaded (i.e. 0% compression) double arrangement were twice those of a double seal compressed to the 20% design compression level. The seals survived an ambient temperature 1000 cycle scrub test over relatively rough Shuttle tile surfaces. The seals were able to disengage and re-engage the edges of the rub surface tiles while being scrubbed over them. Arc jet tests were performed to experimentally determine anticipated seal temperatures for representative flow boundary conditions (pressures and temperatures) under simulated vehicle re-entry conditions. Installation of a single seat in the gap of the test fixture caused a large temperature drop (1710 F) across the seal location as compared to an open gap condition (140 F) confirming the need for seals in the rudder/fin gap location. The seal acted as an effective thermal barrier limiting heat convection through the seal gap and minimizing temperature increases downstream of the seal during maximum heating conditions.

Dunlap, Patrick H., Jr.↗
NASA NTRS2003

Control Surface Seals Investigated for Re- Entry Vehicles

Re-entry vehicles generally use control surfaces (e.g., rudders, body flaps, and elevons) to steer or guide them as they pass into and through the Earth s atmosphere. High temperature seals are required around control surfaces both along hinge lines and in areas where control surface edges seal against the vehicle body to limit hot gas ingestion and the transfer of heat to underlying low-temperature structures. Working with the NASA Johnson Space Center, the Seals Team at the NASA Glenn Research Center completed a series of tests on the baseline seal design for the rudder/fin control surface interfaces of the X-38 vehicle. This seal application was chosen as a case study to evaluate a currently available control surface seal design for applications in future re-entry vehicles. The structures of the rudder/fin assembly and its associated seals are shown in the following illustration.

Dunlap, Patrick H.↗
NASA NTRS2006

Leveraging Existing Mission Tools in a Re-Usable, Component-Based Software Environment

Emerging methods in component-based software development offer significant advantages but may seem incompatible with existing mission operations applications. In this paper we relate our positive experiences integrating existing mission applications into component-based tools we are delivering to three missions. In most operations environments, a number of software applications have been integrated together to form the mission operations software. In contrast, with component-based software development chunks of related functionality and data structures, referred to as components, can be individually delivered, integrated and re-used. With the advent of powerful tools for managing component-based development, complex software systems can potentially see significant benefits in ease of integration, testability and reusability from these techniques. These benefits motivate us to ask how component-based development techniques can be relevant in a mission operations environment, where there is significant investment in software tools that are not component-based and may not be written in languages for which component-based tools even exist. Trusted and complex software tools for sequencing, validation, navigation, and other vital functions cannot simply be re-written or abandoned in order to gain the advantages offered by emerging component-based software techniques. Thus some middle ground must be found. We have faced exactly this issue, and have found several solutions. Ensemble is an open platform for development, integration, and deployment of mission operations software that we are developing. Ensemble itself is an extension of an open source, component-based software development platform called Eclipse. Due to the advantages of component-based development, we have been able to vary rapidly develop mission operations tools for three surface missions by mixing and matching from a common set of mission operation components. We have also had to determine how to integrate existing mission applications for sequence development, sequence validation, and high level activity planning, and other functions into a component-based environment. For each of these, we used a somewhat different technique based upon the structure and usage of the existing application.

Greene, Kevin↗
NASA NTRS2007

Orbiter Gap Filler Bending Model for Re-entry

Pressure loads on a protruding gap filler during an Orbiter reentry are investigated to evaluate the likelihood of extraction due to pressure loads, and to ascertain how much bending will be induced by re-entry pressure loads. Oblique shock wave theory is utilized to develop a representation of the pressure loads induced on a gap filler for the ISSHVFW trajectory, representative of a heavy weight ISS return. A free body diagram is utilized to react the forces induced by the pressure forces. Preliminary results developed using these methods demonstrate that pressure loads, alone, are not likely causes of gap filler extraction during reentry. Assessment of the amount a gap filler will bend over is presented. Implications of gap filler bending during re-entry include possible mitigation of early boundary layer transition concerns, uncertainty in ground based measurement of protruding gap fillers from historical Orbiter flight history, and uncertainty in the use of Orbiter gap fillers for boundary layer prediction calibration. Authors will be added to the author list as appropriate.

Campbell, Charles H.↗