Time-averaged Basis Research Articles

Wavelength-modulation spectroscopy in the mid-infrared for temperature and HCl measurements in aluminum-lithium composite-propellant flames

This work presents the design, development, and application of a laser-absorption-spectroscopy diagnostic capable of providing quantitative, time-resolved measurements of gas temperature and HCl concentration in flames of metallized composite propellants containing ammonium perchlorate (AP) and hydroxyl-terminated polybutadiene (HTPB). This diagnostic utilizes a quantum-well distributed-feedback diode laser emitting near 3.27 μm to measure the absorbance spectra of HCl using a scanned-wavelength-modulation-spectroscopy technique that is insensitive to non-absorbing transmission losses caused by metal particulates in the flame. This diagnostic was applied to characterize the spatial and temporal evolution of temperature and HCl mole fraction in small-scale flames of AP-HTPB composite propellants containing either an aluminum-lithium alloy or micron-scale aluminum. Experiments were conducted at 1 and 10 atm. At both pressures, the flame temperature of the aluminum-lithium propellant, on a time-averaged basis, was 80 to 200 K higher than that of the aluminum propellant (depending on location in the flame) indicating more complete combustion. In addition, the mole fraction of HCl in the aluminum-lithium propellant flame reached values 65–70% lower than the conventional aluminum-propellant flame at the highest measurement location in the flame. The measurements at both pressures showed similar trends in the reduction of HCl in the aluminum-lithium propellant flame but at elevated pressures this occurred on a length scale nearly an order of magnitude smaller than the flame at atmospheric pressure. The results presented further support that the use of an aluminum-lithium alloy is effective at reducing HCl produced by the propellant flame without compromising performance, thereby making it an attractive additive for solid rocket propellants.

Characterization of the influence of aluminum particle size on the temperature of composite-propellant flames using CO absorption and AlO emission spectroscopy

Understanding the temperature of aluminized, composite-propellant flames is critical to achieving robust rocket motor designs and developing accurate, predictive models for propellant combustion. This work presents measurements of (1) the temperature of CO (within the flame bath gas) and (2) the temperature of AlO (located primarily within regions surrounding the burning aluminum particles) within aluminized, composite-propellant flames as a function of height above the burning propellant surface. Three aluminized, ammonium-perchlorate (AP), hydroxyl-terminated polybutadiene (HTPB) composite propellants with varying aluminum particle size (nominally 31 μm, 4.5 μm, or 80 nm) and one non-aluminized AP-HTPB propellant were studied while burning in air at 1 atm. A wavelength-modulation-spectroscopy technique was utilized to measure CO temperature and mole fraction via mid-infrared wavelengths and a conventional AlO emission-spectroscopy technique was utilized to measure the temperature of AlO. The bath-gas temperature varied significantly between propellants, particularly within 2 cm of the burning surface. The propellant with the smallest particles (nano-scale aluminum) had the highest average temperatures and far less variation with measurement location. At all measurement locations, the average bath-gas temperature increased as the initial particle size of aluminum in the propellant decreased, likely due to increased aluminum combustion. The results support arguments that larger aluminum particles can act as a heat sink near the propellant surface and require more time and space to ignite and burn completely. On a time-averaged basis, the temperatures measured from AlO and CO agreed within uncertainty at near 2650 K in the nano-aluminum propellant flame, however, AlO temperatures often exceeded CO temperatures by ≈ 250 to 800 K in the micron-aluminum propellant flames. This result suggests that in the flames studied here, and on a time-averaged basis, the micron-aluminum particles burn in the diffusion-controlled combustion regime, whereas the nano-aluminum particles burn within or very close to the kinetically controlled combustion regime.

Prediction of erosion intermittency using Large Eddy Simulation

The present CFD (Computational Fluid Dynamics) study investigates the triggering of aeolian erosion, which takes place on two transverse sand piles placed in tandem. The URANS (Unsteady Reynolds-averaged Navier-Stokes), DES (Detached Eddy Simulation) and LES (Large Eddy Simulation) approaches are evaluated on their prediction capability of the friction velocity. Each predicted friction velocity is evaluated against a proposed threshold condition, which considers the surface slope along with the near-surface flow direction to be compliant with established recirculation regions.The DES and LES approaches are found to be capable of predicting aeolian erosion intermittency, a phenomenon characterized by burst activity. The URANS approach, by yielding a nearly steady-state solution, predicts erosion only on a time-averaged basis. DES and LES approaches corroborate the reshaping observed in the wind tunnel tests, where the erosion is substantial on the leeward pile and insignificant on the windward one.

Effects of Rotor Tip Blade Loading Variation on Compressor Stage Performance

Changes in loss generation associated with altering rotor tip blade loading of an embedded rotor–stator compressor stage are assessed with unsteady three-dimensional computations, complemented by control volume analyses. Tip-fore-loaded and tip-aft-loaded rotor blades are designed to provide variation in rotor tip blade loading distributions for determining a compressor design hypothesis that aft-loading a rotor blade tip yields a reduction in loss generation in a stage environment. Aft-loading a rotor blade tip delays the formation of tip leakage flow, resulting in a relatively less mixed-out tip leakage flow at the rotor outlet and a reduction in overall tip leakage mass flow, hence a lower loss generation. However, the attendant changes in tip flow angle distribution are such that there is an overall increase in the flow angle mismatch between tip flow and main flow, leading to higher loss generation. The latter outweighs the former; therefore, rotor passage loss from aft-loading a rotor tip is higher unless a constraint is imposed on tip flow angle distribution so that the associated induced loss is negligible. Tip leakage flow, which is not mixed-out at the rotor outlet, is recovered in the downstream stator. The tip leakage flow recovery process yields a higher benefit for a relatively less mixed-out tip leakage flow in the tip-aft-loaded rotor blades on a time-averaged basis. These characterizing parameters together determine the attendant overall loss associated with rotor tip leakage flow in a compressor stage environment. The revised design hypothesis is thus as follows: A rotor should be tip-aft-loaded and hub-fore-loaded while a stator should be hub-aft-loaded and tip-fore-loaded with tip/hub leakage flow angle distribution such that it results in no additional loss. For the compressor stage being assessed here, an estimated 0.15 points enhancement in stage efficiency is possible from aft-loading rotor tip only.

CFD simulation of dilute phase gas–solid riser reactors: Part I—a new solution method and flow model validation

A three-dimensional simulation of a dilute phase riser reactor (solid mass flux: 2 kg m −2 s −1 ) is performed using a novel density based solution algorithm. The model equations consisting of continuity, momentum, energy and species balances for both phases, are formulated following the Eulerian–Eulerian approach. The kinetic theory of granular flow is applied. The gas phase turbulence is accounted for via a k– ε model. An extra transport equation describes the correlation between the gas and solid phase fluctuating motion. The solution algorithm allows a simultaneous integration of all the model equations in contrast to the sequential multi-loop solution in the conventional pressure based algorithms, used so far in riser simulations. The simulations show an unsteady behaviour of the flow, but a core-annulus flow pattern emerges on a time-averaged basis. The abrupt nature of the T type outlets causes a significant recirculation of gas and solid from the top of the riser. The flow near the outlets is highly non-symmetric and has a three-dimensional character. A significant decrease of the gas phase turbulence and particle granular temperature across the riser length is attributed to the presence of small particles, which is qualitatively consistent with the experimental data from literature.

Discrimination of the two diastereoisomeric glycosides heterodendrin and epi-heterodendrin by the combined use of NOE and molecular mechanics

The two glycosides ( S)-heterodendrin and ( R)-epi-heterodendrin were synthesized in a novel, one-step enzymatic synthesis, and separated by means of column chromatography. The 1H NMR spectra of the two diastereoisomers differ mainly in the chemical shift of H-2′ of the side chain. At first sight the 1H NMR spectra do not allow a stereospecific assignment. It was found, however, that the NOE between the anomeric proton H-1 and H-2′ of the side chain is considerably larger in epi-heterodendrin than in heterodendrin, which indicates on a time-averaged basis a smaller distance between these two protons in epi-heterodendrin. This difference in conformational behaviour is correctly reproduced by molecular mechanics calculations, thereby offering a method for the discrimination of these two glycosides.

The effect of flow unsteadiness on the homogeneous nucleation of water droplets in steam turbines

The paper describes a new theory of the formation and growth of water droplets in multistage steam turbines. The essence of the theory is that large-scale static temperature fluctuations caused by the segmentation of blade wakes by successive blade rows have a dominating influence on nucleation and droplet growth in turbines. ‘True’ turbulent fluctuations (due to shear-layer unsteadiness, etc.) are probably less important and are ignored. A Lagrangian frame of reference is adopted and attention is focused on a large number of individual fluid particles during their passage through the turbine. Homogeneous nucleation and growth of droplets in each fluid particle is assumed to be governed by classical theories. All fluid particles are assumed to experience the same pressure variation, but those particles passing close to the blade surfaces suffer greater entropy production and, therefore, have higher static temperatures than those that pursue nearly isentropic paths through the central portions of the blade passages. Particles which suffer high loss therefore nucleate later in the turbine than those that experience little dissipation. Condensation is thus viewed as an essentially random and unsteady phenomenon because the dissipation experienced by a fluid particle in one blade row is assumed to be uncorrelated with its previous history. On a time-averaged basis, the condensation zone is spread over a much greater distance in the flow direction than a simple steady-flow analysis would indicate and may encompass several blade rows, depending on the number of stages in the machine. Predicted droplet size spectra show broad, highly skewed distributions with large mean diameters and sometimes slight bimodality. These are all characteristics of experimentally measured spectra in real turbines. Conventional, steady-flow calculation methods, which predict a fixed Wilson point in a specific blade row and a nearly monodispersed droplet population, cannot reproduce any of these characteristics.

Three-dimensional filamentation of light in laser plasmas

The first calculations of time-dependent laser–plasma filamentation in three dimensions are reported. These calculations are done with a three-dimensional laser propagation code based on a previous two-dimensional code [Phys. Fluids 31, 3079 (1988)]. The effect of incident beam structure, and in particular optical smoothing techniques, on the behavior of filamentation is studied. Both ponderomotive and thermal conduction dominated nonlinearities are considered, and calculations are done simulating both homogeneous nonabsorbing plasmas and inhomogeneous laboratory plasmas. Random phase screen (RPS) and induced spatial incoherence (ISI) optical smoothing techniques are investigated and compared to generic unsmoothed laser beams. Qualitative examples are presented and scaling studies are done and compared to a simple theoretical analysis. In typical laser–plasma interactions without optical smoothing, three-dimensional effects lead to greatly increased filament intensities, as expected. Peak filament intensities of order 100–500 times the average intensity are routinely observed (without optical smoothing), as compared to earlier two-dimensional calculations where peak intensities were of order 10–50 times average. In spite of this tendency to create stronger filaments, three-dimensional filamentation (when measured on a time-averaged basis) can be suppressed by using ISI smoothing. Under the same conditions, instantaneous ISI intensities can show considerable enhancement, although much less than the unsmoothed beams. RPS smoothing exhibits less filamentation suppression. Under laser-fusion reactor conditions, calculations indicate that ISI suppression can completely eliminate filamentation.

Platinum silicide contact to arsenic-doped polycrystalline silicon: H-C W Huang et al, J appl Phys, 63, 1988, 1111–1116

Post-glacial tholeiitic basalts from the western Reykjanes Peninsula range from picrite basalts (oldest) to olivine tholeiites to tholeiites (youngest). In this sequence there are large systematic variations in rare earth element (REE) abundances (La/Sm normalized to chondrites ranges from 0.33 in the picrite basalts to 1.25 in the fissure tholeiites) and corresponding variations in 143Nd/144Nd (0.51317 in the picrite basalts to 0.51299 in the fissure tholeiites). The large viaration in 143Nd/144Nd, more than one-third the total range observed in most ocean islands and mid-ocean ridge basalts (MORB), is accompanied by only a small variation in 87Sr/86Sr (0.7031–0.7032). These 87Sr/86Sr ratios are within the range of other Icelandic tholeiites, and distinct from those of MORB.We conclude that the mantle beneath the Reykjanes Peninsula is heterogeneous with respect to relative REE abundances and 143Nd/144Nd ratios. On a time-averaged basis all parts of this mantle show evidence of relative depletion in light REE. Though parts of this mantle have REE abundances and Nd isotope ratios similar to the mantle source of “normal” MORB, 87Sr/86Sr is distinctly higher. Unlike previous studies we find no evidence for chondritic relative REE abundances in the mantle beneath the Reykjanes Peninsula; in fact, the data require significant chemical heterogeneity in the hypothesized mantle plume beneath Iceland, as well as lateral mantle heterogeneity from the Reykjanes Ridge to the Reykjanes Peninsula. The compositional range of the Reykjanes Peninsula basalts is consistent with mixing of magmas produced by different degrees of melting in different parts of the heterogeneous mantle source beneath the Reykjanes Peninsula.

Cavities in proteins: structure of a metmyoglobin-xenon complex solved to 1.9 A.

X-ray crystallographic data to 1.9-A resolution were collected on sperm whale metmyoglobin equilibrated with 7 atm of xenon gas. The results indicate four xenon sites of occupancy from 0.45 to 1.0. These sites are located in interior spaces or packing defects of the myoglobin molecule. The effects of the bound xenon on the protein structure are minor, and we observe a small overall reduction in refined isotropic atomic protein temperature factors. We interpret the results as a confirmation that, on a time-averaged basis, cavities exist within the myoglobin molecule and suggest that the binding of small ligands in these cavities affects the internal motions and conformational substrates of the protein.

Weathering of Mars: Antarctic analog studies

Terrestrial analog studies of potential Martian weathering processes are reported. Four major weathering environments are identified: (i) hydrothermal alteration of impact melt sheets and impact breccias, (ii) solid-gas and related reactions, (iii) subpermafrost intrusion of lavas involving liquid water, and (iv) subaerial extrusion of lavas in the absence of liquid water. Weathering in environments (i)−(iii) has been discussed by other authors; this report discusses weathering in environment (iv), an analog of which is Antarctica. We conclude that weathering is geologically slow in the absence of liquid water, and that zeolites predominate over clays as secondary minerals. On volumetric grounds it appears that hydrothermal alteration of impact melt sheets should be the most important time-averaged weathering mechanism, provided that H2O was present as liquid or permafrost. Such hydrothermal alteration should operate predominately on ancient crustal material. Gas-solid reactions and photochemical weathering should also operate primarily on ancient crustal material on a time-averaged basis. Weathering products of younger subpermafrost or subaerially erupted basalts should be subordinate to hydrothermal alteration and gas-solid reactions. It appears that the present Martian regolith as analyzed by the Viking landers contains a major contribution from ancient crust as typified today by the southern cratered highlands, with a lesser contribution from the younger, hemispherically restricted basaltic lavas.

Nd and Sr isotope ratios and rare earth element abundances in Reykjanes Peninsula basalts evidence for mantle heterogeneity beneath Iceland

Post-glacial tholeiitic basalts from the western Reykjanes Peninsula range from picrite basalts (oldest) to olivine tholeiites to tholeiites (youngest). In this sequence there are large systematic variations in rare earth element (REE) abundances (La/Sm normalized to chondrites ranges from 0.33 in the picrite basalts to 1.25 in the fissure tholeiites) and corresponding variations in 143Nd/ 144Nd (0.51317 in the picrite basalts to 0.51299 in the fissure tholeiites). The large viaration in 143Nd/ 144Nd, more than one-third the total range observed in most ocean islands and mid-ocean ridge basalts (MORB), is accompanied by only a small variation in 87Sr/ 86Sr (0.7031–0.7032). These 87Sr/ 86Sr ratios are within the range of other Icelandic tholeiites, and distinct from those of MORB. We conclude that the mantle beneath the Reykjanes Peninsula is heterogeneous with respect to relative REE abundances and 143Nd/ 144Nd ratios. On a time-averaged basis all parts of this mantle show evidence of relative depletion in light REE. Though parts of this mantle have REE abundances and Nd isotope ratios similar to the mantle source of “normal” MORB, 87Sr/ 86Sr is distinctly higher. Unlike previous studies we find no evidence for chondritic relative REE abundances in the mantle beneath the Reykjanes Peninsula; in fact, the data require significant chemical heterogeneity in the hypothesized mantle plume beneath Iceland, as well as lateral mantle heterogeneity from the Reykjanes Ridge to the Reykjanes Peninsula. The compositional range of the Reykjanes Peninsula basalts is consistent with mixing of magmas produced by different degrees of melting in different parts of the heterogeneous mantle source beneath the Reykjanes Peninsula.

Synthesis of alphavirus-specified RNA.

UV irradiation of chicken fibroblasts infected with Semliki Forest or Sindbis virus has been used to investigate the mechanism of synthesis of 42S and 26S RNA, the major plus-strand virus-specified RNAs formed during the multiplication of standard virus particles. From an analysis of the kinetics of UV inactivation of the synthesis of these two RNAs, we conclude (i) that 26S RNA is formed by internal transcriptive initiation from a point about two-thirds of the way from the 3' end of the 42S negative-strand template; (ii) that there exists a population of plus-strand synthesizing complexes whose members are each capable of synthesizing both 42S and 26S RNA; and (iii) that, on a time-averaged basis, each complex in wild-type virus-infected cells contains one virus polymerase mediating 42S RNA synthesis and three mediating 26S RNA synthesis. The RNA phenotypes of 15 RNA(-)ts mutants of Sindbis virus have been examined after temperature shift to the restrictive temperature. Under these conditions, cells infected with three mutants, N2, N7, and E268, synthesized four to six times as much 42S RNA (relative to 26S RNA) as wild-type virus-infected cells. These studies were extended by examining, in detail, the RNA and polypeptide phenotypes of mutants N2 and E268. These experiments showed that, in N2- and E268-infected cells, one of the virus-specified nonstructural (NS) polypeptides (NS p89; H. Brzeski and S. I. T. Kennedy, J. Virol. 22:420-429, 1977) is thermolabile after shift up to restrictive temperature. This finding, together with the observation that, after shift, the 26S/42S RNA ratio in N2-infected cells changes markedly in favor of 42S RNA synthesis, leads us to conclude that, of the three NS polypeptides, NS p89 modulates 26S RNA synthesis.

Automatic gas chromatographic measurement of C 1–C 5 hydrocarbons in air

The development of an automatic gas Chromatographic method for measurement of hydrocarbons in air is described. With this method an important fraction of the hydrocarbons in the atmosphere, the C 1–C 5 hydrocarbons, can be separated and measured on a time-averaged basis. Compared with other measuring methods for hydrocarbons it is a relatively simple, direct and inexpensive method for sensitive and quick measurement. The high sensitivity of this method and the relative freedom from interference, compared for example with similar commercial apparatus, can be attributed to a number of apparently small, supplementary provisions. After a discussion of the reasons for the selection of our method and a description of the apparatus, including technical data, reference is made to analytical results intended to give an impression of the possibilities of the apparatus.