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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

High Temperature Transfer Molding Resins Based on 2,3,3',4'-Biphenyltetracarboxylic Dianhydride

As part of an ongoing effort to develop materials for resin transfer molding (RTM) processes to fabricate high performance/high temperature composite structures, phenylethynyl containing imides have been under investigation. New phenylethynyl containing imide compositions were prepared using 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA) and evaluated for cured glass transition temperature (Tg), melt flow behavior, and for processability into flat composite panels via RTM. The a-BPDA imparts a unique combination of properties that are desirable for high temperature transfer molding resins. In comparison to its symmetrical counterpart (i.e. 3,3',4,4'-biphenyltetracarboxylic dianhydride), a-BPDA affords oligomers with lower melt viscosities and when cured, higher Tgs. Several candidates exhibited the appropriate combination of properties such as a low and stable melt viscosity required for RTM processes, high cured Tg, and moderate toughness. The chemistry, physical, and composite properties of select resins will be discussed.

Smith, J. G., Jr.↗
NASA NTRS2004

Modeling the VARTM Composite Manufacturing Process

A comprehensive simulation model of the Vacuum Assisted Resin Transfer Modeling (VARTM) composite manufacturing process has been developed. For isothermal resin infiltration, the model incorporates submodels which describe cure of the resin and changes in resin viscosity due to cure, resin flow through the reinforcement preform and distribution medium and compaction of the preform during the infiltration. The accuracy of the model was validated by measuring the flow patterns during resin infiltration of flat preforms. The modeling software was used to evaluate the effects of the distribution medium on resin infiltration of a flat preform. Different distribution medium configurations were examined using the model and the results were compared with data collected during resin infiltration of a carbon fabric preform. The results of the simulations show that the approach used to model the distribution medium can significantly effect the predicted resin infiltration times. Resin infiltration into the preform can be accurately predicted only when the distribution medium is modeled correctly.

Song, Xiao-Lan↗
NASA NTRS2005

An Experimental Study of n-Heptane and JP-7 Extinction Limits in an Opposed Jet Burner

Propulsion engine combustor design and analysis requires experimentally verified data on the chemical kinetics of fuel. Among the important data is the combustion extinction limit as measured by observed maximum flame strain rate. The extinction limit relates to the ability to maintain a flame in a combustor during operation. Extinction limit data can be obtained for a given fuel by means of a laminar flame experiment using an opposed jet burner (OJB). Laminar extinction limit data can be applied to the turbulent application of a combustor via laminar flamelet modeling. The OJB consists of two axi-symmetric tubes (one for fuel and one for oxidizer), which produce a flat, disk-like counter-flow diffusion flame. This paper presents results of experiments to measure extinction limits for n-heptane and the military specification fuel JP-7, obtained from an OJB. JP-7 is an Air Force-developed fuel that continues to be important in the area of hypersonics. Because of its distinct properties it is currently the hydrocarbon fuel of choice for use in Scramjet engines. This study provides much-desired data for JP-7, for which very little information previously existed. The interest in n-heptane is twofold. First, there has been a significant amount of previous extinction limit study and resulting data with this fuel. Second, n-heptane (C7H16) is a pure substance, and therefore does not vary in composition as does JP-7, which is a mixture of several different hydrocarbons. These two facts allow for a baseline to be established by comparing the new OJB results to those previously taken. Additionally, the data set for n-heptane, which previously existed for mixtures up to 26 mole percent in nitrogen, is completed up to 100% n-heptane. The extinction limit data for the two fuels are compared, and complete experimental results are included.

Convery, Janet L.↗
NASA NTRS1977

Quiet Clean Short-haul Experimental Engine (QCSEE). Aerodynamic and aeromechanical performance of a 50.8 cm (20 inch) diameter 1.34 PR variable pitch fan with core flow

The fan aerodynamic and aeromechanical performance tests of the quiet clean short haul experimental engine under the wing fan and inlet with a simulated core flow are described. Overall forward mode fan performance is presented at each rotor pitch angle setting with conventional flow pressure ratio efficiency fan maps, distinguishing the performance characteristics of the fan bypass and fan core regions. Effects of off design bypass ratio, hybrid inlet geometry, and tip radial inlet distortion on fan performance are determined. The nonaxisymmetric bypass OGV and pylon configuration is assessed relative to both total pressure loss and induced circumferential flow distortion. Reverse mode performance, obtained by resetting the rotor blades through both the stall pitch and flat pitch directions, is discussed in terms of the conventional flow pressure ratio relationship and its implications upon achievable reverse thrust. Core performance in reverse mode operation is presented in terms of overall recovery levels and radial profiles existing at the simulated core inlet plane. Observations of the starting phenomena associated with the initiation of stable rotor flow during acceleration in the reverse mode are briefly discussed. Aeromechanical response characteristics of the fan blades are presented as a separate appendix, along with a description of the vehicle instrumentation and method of data reduction.

Giffin, R. G.↗
NASA NTRS2006

On the Need for Multidimensional Stirling Analysis

Contents include the following: Dual opposed convertors. High efficiency. Low mass space power. One-dimensional analysis. Fast computation. Design optimizations are easily done. Need for multidimensional modeling. Axisymmetric simulation. Flow characteristics. Low mach number. Laminar, transitional, and turbulent flow. Conjugate heat transfer. Third order analysis. Recent whole engine modeling. Regenerator geometry. Turbulence modeling. Flat head heater not 1-D. Empirical coefficients needed. Experiment design. Flow distribution. Sensor placement. Calibration. Validation.

Dyson, Rodger↗
NASA NTRS1996

Surface Tension Driven Convection Experiment-2 (STDCE-2

The surface tension driven convection experiment-2 (STDCE-2) was conducted onboard the U.S. Microgravity Laboratory (USML)-2 Spacelab which was launched on October 20, 1995. The main objectives of the experiment was to study oscillatory thermocapillary flows in microgravity. Thermocapillary flows were generated in cylindrical test chambers filled with 2 centistokes silicone oil. Six modules were used to study three different chamber diameters and two different heating modes. Tests with both flat and curved free surfaces were conducted. The flow field was studied by flow visualization and an infrared imaging system recorded the oil free-surface temperature. An optical (Ronchi) system was used to measure the oil free-surface deformation and motions. A total of 55 tests were conducted and oscillations were found in most of them. The data are being analyzed.

Ostrach, Simon↗
NASA NTRS2003

A Reassessment of the Emplacement and Erosional Potential of Turbulent, Low-Viscosity Lavas on the Moon

We have reevaluated the role of thermal erosion by low-viscosity lunar lavas as a mechanism or the formation of the lunar sinuous rilles. We have adapted the model of Williams et aL and used the compositions of an Apollo 12 basalt and a terrestrial komatiitic basalt to investigate the compositional and environmental effects on the flow behavior of low-viscosity lavas on the Moon and Earth. Our model predict that lunar lava could have erupted as turbulent flows that were capable of flowing hundreds of kilometers on a sufficiently flat, unobstructed substrate. These results are consistent with previous studies. Modeling of lava over a substrate of the same composition shows that thermal erosion rates would have been low (approx. 10 cm/d). As a result, long-duration eruptions (approximately months to years) would have been required to incise deep (tens to hundreds of meters) channels. Partial melting and mechanical removal of the substrate, a mechanism suggested by Hulme to enhance erosion, only slightly increases thermal erosion rules. Other factors, such as higher flow rates or lava superheating, could have produced deep rilles by thermal erosion during shorter-duration eruption. A superheated lunar lava not only would have had a higher erosion rate (approx. 40 cm/d) but also would have remained uncrusted for tens of kilometers, which is consistent with the open channel morphology of most sinuous rilles. For lunar lavas with large volatile (t.e., vesicle) contents, the presence of vesicles would have tended to increase viscosity at low strain rates, resulting in shorter turbulent flow distances, lower thermal erosion rates, and thus shallower erosion channel depths for given eruption durations.

William, David A.↗
NASA NTRS2017

Plateaus and Sinuous Ridges as the Fingerprints of Lava Flow Inflation in the Eastern Tharsis Plains of Mars

The Tharsis Montes rift aprons are composed of outpourings of lava from chaotic terrains to the northeast and southwest flank of each volcano. Sinuous and branching channel networks that are present on the rift aprons suggest the possibility of fluvial processes in their development, or erosion by rapidly emplaced lavas, but the style of lava flow emplacement throughout rift apron development is not clearly understood. To better characterize the style of lava emplacement and role of fluvial processes in rift apron development, we conducted morphological mapping of the Pavonis Mons southwest rift apron and the eastern Tharsis plains using images from the High Resolution Imaging Science Experiment (HiRISE), Mars Orbiter Camera (MOC), Context Camera (CTX), Thermal Emission Imaging System (THEMIS), and High Resolution Stereo Camera (HRSC) along with the Mars Orbiter Laser Altimeter (MOLA) Precision Experiment Data Records (PEDRs) and gridded data. Our approach was to: (1) search for depositional fans at the slope break between the rift apron and adjacent low slope plains; (2) determine if there is evidence that previously formed deposits might have been buried by plains units; (3) characterize the Tharsis plains morphologies east of Pavonis Mons; and (4) assess their relationship to the rift apron units. We have not identified topographically significant depositional fans, nor did we observe evidence to suggest that plains units have buried older rift apron units. Flow features associated with the rift apron are observed to continue across the slope break onto the plains. In this area, the plains are composed of a variety of small fissures and low shield vents around which broad channel-fed and tube-fed flows have been identified. We also find broad, flat-topped plateaus and sinuous ridges mixed among the channels, tubes and vents. Flat-topped plateaus and sinuous ridges are morphologies that are analogous to those observed on the coastal plain of Hawai'i, where lava flows have advanced from the volcano's several degree flank onto the nearly zero degree coastal plain. When local volumetric flow rates are low, flow fronts tend to spread laterally and often thicken via endogenous growth, or inflation, of the sheet-like flow units. If flow advance is restricted by existing topography into narrow pathways, inflation can be focused into sinuous, elongate ridges. The presence of plateaus and ridges-emplaced from the rift zones, across the plains to the east of Pavonis Mons-and a lack of fan-like features, or evidence for their burial, are consistent with rift apron lavas crossing a slope break with low local volumetric flow rates that led to inflation of sheet-like and tube-fed lava flows.

Bleacher, Jacob E.↗
NASA NTRSDate not supplied

Opposed-flow Spreading Flames: Effect of Sub-atmospheric Pressure on Spread and Burning Rates

Flame spread over solid fuels is a canonical problem in fire science, due to its direct implications on material flammability and importance in fire development. Flames in a microgravity environment can behave very differently than on Earth, posing additional risks for spaceflight life safety. Sub-atmospheric pressures in ground-based experiments have been proposed to approximately replicate the burning behavior of solid fuels in reduced gravity conditions because of similar effects on heat and mass transfer mechanisms from the flame to the solid. In opposed-flow flame spread, the solid fuel is heated by the flame ahead of its leading edge, and this process is strongly affected by the ambient conditions. In this work, we consider flames spreading over flat thin acrylic samples exposed to a forced flow of 20 cm/s, and pressures between 30 and 100 kPa. When radiation losses and chemical kinetic effects are neglected, experimental and theoretical results suggest an independence of the spread rate on pressure. However, the spread rate shows a decreasing trend with lower pressure in the range 30-60 kPa. The mass burning rate, calculated from the samples weight measured before and after the experiments, shows a similar trend. The flame length, on the other hand, shows a non-monotonic behavior, reaching a maximum at 60 kPa. Additionally, gas emissions measured during the experiments are used to estimate the heat release rate of the spreading flames. The comparison of the heat release rate obtained from the measured emissions and the estimated mass burning rates, suggests that chemical kinetics is not driving the decrease in flame spread observed at low pressures, whereas radiation losses could be responsible in analogy to what has been observed in micro and partial gravity studies. These results could provide more information to guide future Earth-based material flammability testing for spacecraft applications.

fire↗
NASA NTRS2003

Study of Unsteady Flows with Concave Wall Effect

This paper presents computational fluid dynamic studies of the inlet turbulence and wall curvature effects on the flow steadiness at near wall surface locations in boundary layer flows. The time-stepping RANS numerical solver of the NASA Glenn-HT RANS code and a one-equation turbulence model, with a uniform inlet turbulence modeling level of the order of 10 percent of molecular viscosity, were used to perform the numerical computations. The approach was first calibrated for its predictabilities of friction factor, velocity, and temperature at near surface locations within a transitional boundary layer over concave wall. The approach was then used to predict the velocity and friction factor variations in a boundary layer recovering from concave curvature. As time iteration proceeded in the computations, the computed friction factors converged to their values from existing experiments. The computed friction factors, velocity, and static temperatures at near wall surface locations oscillated periodically in terms of time iteration steps and physical locations along the span-wise direction. At the upstream stations, the relationship among the normal and tangential velocities showed vortices effects on the velocity variations. Coherent vortices effect on the velocity components broke down at downstream stations. The computations also predicted the vortices effects on the velocity variations within a boundary layer flow developed along a concave wall surface with a downstream recovery flat wall surface. It was concluded that the computational approach might have the potential to analyze the flow steadiness in a turbine blade flow.

Wang, Chi R.↗
DOE OSTI2024

Experimental investigation of surface roughness/wettability pattern effect on crystallization fouling over falling-film flow

In many industries, including desalination, scaling in heat exchangers is a persistent issue, and most methods of scaling control involve environmentally hazardous chemical additives. Exploiting the effects of surface features and flow-imposed shear on salt deposition might introduce a new approach to scale management, opening the possibility of self-cleaning surfaces. In this work, we experimentally explore surface roughness and wettability patterns interaction with salt deposition and flow shear. Heat transfer and scale mass deposition on flat surfaces are measured during thin-film evaporation of calcium sulfate solution. A wide range of surface roughness (0.027–2.66 μm) is studied at fixed flow and heat flux conditions. Due to improved mixing, heat transfer is enhanced with rougher surfaces initially; however, degrades more quickly than smoother surfaces. Following a period of initial mass deposition fluctuation, a steady scaling stage is observed, with rough surfaces scaling more than smooth surfaces. Wettability patterned surfaces can suppress crystal nucleation without sacrificing overall surface wetting, resulting in antifouling performance and heat transfer enhancement. Scale mass deposition on a patterned surface is reduced by 60 %, and 27 % heat transfer improvement over the baseline surface is found. Furthermore, this study provides guidance to surface manipulation for heat transfer improvement and fouling mitigation.

42 ENGINEERING↗
DOE OSTI2021

Evaluation of idealized large-eddy simulations performed with the Weather Research and Forecasting model using turbulence measurements from a 250 m meteorological mast

Abstract. We investigate the ability of the Weather Research and Forecasting model to perform large-eddy simulation of canonical flows. This is achieved through comparison of the simulation outputs with measurements from sonic anemometers on a 250 m meteorological mast located at Østerild, in northern Denmark. Østerild is on a flat and rough area, and for the predominant wind directions, the atmospheric flow can be considered to be close to homogeneous. The idealized simulated flows aim at representing atmospheric boundary layer turbulence under unstable, neutral, and stable stability conditions at the surface, which are statistically significant conditions observed at Østerild. We found that the resolved fields from the simulations appear to have the characteristics of the three stability regimes. Vertical profiles of observed mean wind speeds and direction are well reproduced by the simulations, with the largest differences under near-neutral conditions, where the effect of the subgrid-scale model is evident on the vertical wind shear close to the surface. Vertical profiles of observed eddy fluxes are also well reproduced by the simulations, with the largest differences for the three velocity component variances under stable stability conditions, although nearly always within the observed variability. With regards to turbulent kinetic energy, we find good agreement between observations and simulations at all vertical levels. Simulated and observed velocity spectra match very well and show very similar behavior with height and with atmospheric stability within the low-frequency interval; at the effective resolution, the simulated spectra show the typical drop-off of finite differences. Our findings demonstrate that these idealized simulations reproduce the characteristics of atmospheric stability regimes often observed at a high turbulent and flat site within a direction sector, where the air flows over nearly homogeneous land.

17 WIND ENERGY↗
DOE OSTI2022

Numerical algorithms for water waves with background flow over obstacles and topography

Abstract We present two accurate and efficient algorithms for solving the incompressible, irrotational Euler equations with a free surface in two dimensions with background flow over a periodic, multiply connected fluid domain that includes stationary obstacles and variable bottom topography. One approach is formulated in terms of the surface velocity potential while the other evolves the vortex sheet strength. Both methods employ layer potentials in the form of periodized Cauchy integrals to compute the normal velocity of the free surface, are compatible with arbitrary parameterizations of the free surface and boundaries, and allow for circulation around each obstacle, which leads to multiple-valued velocity potentials but single-valued stream functions. We prove that the resulting second-kind Fredholm integral equations are invertible, possibly after a physically motivated finite-rank correction. In an angle-arclength setting, we show how to avoid curve reconstruction errors that are incompatible with spatial periodicity. We use the proposed methods to study gravity-capillary waves generated by flow around several elliptical obstacles above a flat or variable bottom boundary. In each case, the free surface eventually self-intersects in a splash singularity or collides with a boundary. We also show how to evaluate the velocity and pressure with spectral accuracy throughout the fluid, including near the free surface and solid boundaries. To assess the accuracy of the time evolution, we monitor energy conservation and the decay of Fourier modes and compare the numerical results of the two methods to each other. We implement several solvers for the discretized linear systems and compare their performance. The fastest approach employs a graphics processing unit (GPU) to construct the matrices and carry out iterations of the generalized minimal residual method (GMRES).

Ambrose, David M.↗
NASA NTRS1987

Solar Pump

Proposed pump moves liquid by action of bubbles formed by heat of sun. Tube of liquid having boiling point of 100 to 200 degrees F placed at focal axis of cylindrical reflector. Concentrated sunlight boils liquid at focus, and bubbles of vapor rise in tube, carrying liquid along with them. Pressure difference in hot tube sufficient to produce flow in large loop. Used with conventional flat solar heating panel in completely solar-powered heat-storage system.

Pique, Charles↗
NASA NTRS1993

Control of unsteady shock-induced turbulent boundary layer separation upstream of blunt fins

Fluctuating wall pressure measurements have been made on centerline upstream of blunt fins in a Mach 5 turbulent boundary layer. Standard time series analysis and conditional sampling algorithms have been used to examine the effects of leading edge sweepback, leading edge shape, and fin root modifications on the fluctuating pressures. Leading edge sweep considerably reduces the mean and rms pressure loading at the fin root, the extent of the region of unsteady separation shock motion, and the separation length. The frequency of pressure fluctuations in the intermittent region increases with leading edge sweepback, while the spectral content of pressure fluctuations in the separated region is virtually unchanged by leading edge sweep. A swept hemicylindrically blunted root fillet reduces the centerline upstream influence and intermittent region length by 50 percent, and reduces the mean and rms pressure loading at the fin root by about 75 percent and 95 percent respectively. Experiments using hemicylindrical, wedge shaped and flat leading edges show that while separated flow scales increase with increasing 'bluntness', intermittent region length and root loading decrease, and separation shock frequency increases.

Kleifges, K.↗
NASA NTRS2000

RFI and SCRIMP Model Development and Verification

Vacuum-Assisted Resin Transfer Molding (VARTM) processes are becoming promising technologies in the manufacturing of primary composite structures in the aircraft industry as well as infrastructure. A great deal of work still needs to be done on efforts to reduce the costly trial-and-error methods of VARTM processing that are currently in practice today. A computer simulation model of the VARTM process would provide a cost-effective tool in the manufacturing of composites utilizing this technique. Therefore, the objective of this research was to modify an existing three-dimensional, Resin Film Infusion (RFI)/Resin Transfer Molding (RTM) model to include VARTM simulation capabilities and to verify this model with the fabrication of aircraft structural composites. An additional objective was to use the VARTM model as a process analysis tool, where this tool would enable the user to configure the best process for manufacturing quality composites. Experimental verification of the model was performed by processing several flat composite panels. The parameters verified included flow front patterns and infiltration times. The flow front patterns were determined to be qualitatively accurate, while the simulated infiltration times over predicted experimental times by 8 to 10%. Capillary and gravitational forces were incorporated into the existing RFI/RTM model in order to simulate VARTM processing physics more accurately. The theoretical capillary pressure showed the capability to reduce the simulated infiltration times by as great as 6%. The gravity, on the other hand, was found to be negligible for all cases. Finally, the VARTM model was used as a process analysis tool. This enabled the user to determine such important process constraints as the location and type of injection ports and the permeability and location of the high-permeable media. A process for a three-stiffener composite panel was proposed. This configuration evolved from the variation of the process constraints in the modeling of several different composite panels. The configuration was proposed by considering such factors as: infiltration time, the number of vacuum ports, and possible areas of void entrapment.

Loos, Alfred C.↗
NASA NTRS2002

Bridgman Growth of Germanium Crystals in a Rotating Magnetic Field

A series of (100)-oriented gallium-doped germanium crystals have been grown by the Bridgman method and under the influence of a rotating magnetic field (RMF). The RMF has a marked affect on the interface shape, changing it from concave to nearly flat. The onset of time-dependent flow instabilities occurs when the critical magnetic Taylor number is exceeded, and this can be observed by noting the appearance of striations in the grown crystals. The critical magnetic Taylor number is a sensitive function of the aspect ratio and, as the crystal grows under a constant applied magnetic field, the induced striations change from nonperiodic to periodic, undergo a period-doubling transition, and then cease to exist. Also, by pulsing the RMF on and off, it is shown that intentional interface demarcations can be introduced.

Volz, M. P.↗