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At least 271 records · Page 15

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NASA NTRS1983

Peptide and non-peptide opioid-induced hyperthermia in rabbits

The intracerebroventricular administration of prototype nonpeptide opioid receptor (mu, kappa, and sigma) agonists, morphine, ketocyclazocine, and N-allyl-normetazocine was found to induce hyperthermia in rabbits. The similar administration of peptide opioids like beta-endorphin (BE), methionine-enkephalin (ME), and its synthetic analogue D-ala2-methionine-enkephalinamide (DAME) was also found to cause hyperthermia. Results indicate that only the liver-like transport system is important to the ventricular inactivation of BE and DAME. Prostaglandins and norepinephrine were determined not to be involved in peptide and nonpeptide opioid-induced hyperthermia. In addition, cAMP was not required since a phosphodiesterase inhibitor, theophylline, did not accentuate the hyperthermia due to peptide and nonpeptide opioids. Naloxone-sensitive receptors were found to be involved in the induction of hyperthermia by morphine, BE, ME, and DAME since naloxone attenuated them. However, the hyperthermic response to ketocyclazocine and N-allyl-normetazocine was not antagonized by naloxone.

Kandasamy, S. B.↗

NASA NTRS1982

Investigation of effects of microphone position and orientation on near-ground noise measurements

Three ground level microphone mounting techniques (flush mounting, inverting the microphone over a plate, and lying the microphone on a plate) were compared over a frequency range from 315 Hz to 20 kHz and over a wide range of incidence angles in the Langley Jet-Noise Laboratory anechoic room. The flush mounted microphone, when compared with a free field microphone, exhibited approximate pressure doubling up to a frequency of 10 kHz. At frequencies less than 4 kHz, the inverted and lying microphones were in good agreement with the flush mounted microphone, and their 1/3-octave-band response spectra were fairly insensitive to the position of the microphone. At higher frequencies, the geometry of the microphone and its mounting became important. The inverted microphone 0.5 times the diameter above the plate gave the flattest response compared with the flush mounted microphone. Nondimensional analysis of the inverted and lying results showed that for Kappa H cos theta 0.7 the response of the microphones approached that of the flush mounted microphone.

Willshire, W. L., Jr.↗

NASA NTRS1984

The application of vortex theory to the optimum swept propeller

It is shown that an optimum propeller generating a swept wake must satisfy the Betz condition, at least to a first order. A numerical solution for swept propellers generating a rigid helicoidal wake is formulated and some results are presented. These results indicate that sweep has a significant effect on Goldstein's kappa factor, particularly at high advance ratios typical of those at which advanced turboprops operate.

Mccormick, B. W.↗

NASA NTRS1983

The nature of stellar active regions

Observational estimates of chromospheric radiative loss rates in Ca II H and K in main-sequence F, G, and K dwarfs are used to compare stars that span a range of activity levels with each other and with the sun. For stars with spectral types similar to that of the sun, it is found that chromospheric radiative losses in stars with active chromospheres exceed the flux emitted by plages on the sun at solar maximum by about a factor of 6. If this difference is due primarily to a difference in the fraction of the stellar surface covered by plage-like material, and not to a change in the character of the emission-line regions, then more than half of the stellar surface in stars with large chromospheric radiative loss rates must be covered by active regions. It is also possible to show that active regions in young solar-type stars extend at least to latitudes + or - 25 deg from the rotational equator and that a typical individual region contributes no more than 2 percent - 3 percent of the total H and K emission. In Kappa Cet, observations show that the rotational modulation persisted in both phase and amplitude for at least 100 days (12 rotation cycles).

Wolff, S. C.↗

NASA NTRS1984

An Excitation Mechanism for Solar 5-minute Oscillations of Intermediate and High Degree

The overstability of acoustic modes trapped in the solar convection zone is studied with mechanical and thermal effects of turbulence included, in an approximate manner, through the eddy transport coefficients. Many of these acoustic modes are found to be overstable with the most rapidly growing modes occupying a region centered around 3.2 mHz and spread over a wide range of length-scales. The numerical results are in reasonable accord with the observed power-spectrum of the five-minute oscillations of intermediate and high degree. The oscillations are probably driven by a simultaneous operation of the kappa-mechanism and the turbulent conduction (convective Cowling) mechanism, the dominant contribution to the generation of self-excited acoustic waves arising from the convective Cowling mechanism.

Antia, H. M.↗

NASA NTRS1985

The local characteristic function of interplanetary particle propagation

An easily measurable intensity function which characterizes the interplanetary propagation of charged solar flare particles is presented. This function is nearly time invariant during a solar event despite the large variations of intensity and anisotropy, but varies from event to event. It characterizes the systematic and stochastic forces of the interplanetary magnetic field which focus and scatter the particles in pitch angle. The model of focused transport shows that this function is essentially determined by the local shape and amplitude of the pitch angle diffusion coefficient kappa (mu) and by the local value of the focusing length. The time profile of the solar particle injection is typically of negligible influence. The local characteristic function may be used as a powerful new tool for a systematic analysis of flare particle angular distributions, Examples are given.

Green, G.↗

NASA NTRS1983

On the localized nature of the Galactic cosmic rays

The escape of cosmic rays from the Galaxy at rigidities above and below 10 GV/c is investigated theoretically using a model with a diffusion coefficient of (1-10) x 10 to the 26th sq cm/sec (at 10 GV/c) and various values of the exponent delta. Some numerical results are presented in graphs, and it is found that at low energies the source nearest to the earth is at a distance of 100-300 pc, while the higher-energy diffusion length is 1-10 kpc (assuming in both cases that the diffusive medium is homogeneous and has a characteristic size greater than the respective lengths). For the case of a smaller storage volume, the lifetime to reach the boundary is inversely proportional to kappa.

Ormes, J. F.↗

NASA NTRS1985

Turbulence modelling for complex shear flows

The turbulence models available for the prediction of complex turbulent shear layers are reviewed in this paper, concentrating mainly on three-dimensional flows, flows subjected to curvature and body rotation, separated flows, and vortex flows. A critical review of zero-equation, one-equation, two-equation, algebraic Reynolds stress, and full Reynolds stress models are carried out, with a specific emphasis on their applicability to complex flows. It is concluded that algebraic eddy viscosity models and kappa-epsilon/kappa-omega models, with a constant value of coefficients, are not adequate for complex flows. The models which include a description of stresses, either through an algebraic Reynolds stress model or a full Reynolds stress model, are essential for adequate prediction of these flows. It is recommended that systematic experimental investigations be carried out to isolate various complex interactions in order to understand and model the various effects and to carry out an extension of the present models to include complex flows.

Lakshminarayana, B.↗

NASA NTRS1985

Computations of internal turbulent flow with large separated flow regions

An implicit two-equation turbulence solver in generalized coordinates has been developed and is used in conjunction with the three-dimensional incompressible Navier-Stokes solver, INS3D, to calculate the internal flow in one channel and in an additional channel with a sudden 2:3 expansion. A new and consistent boundary procedure for a low Reynolds number form of the kappa-epsilon turbulence model is chosen to integrate the equations up to the wall. The high Reynolds number form of the equations are integrated using wall functions. The latter approach yields a faster convergence to the steady state solution than the former. For the case of channel flow, both the wall function and wall boundary condition approaches yield results in good agreement with the experimental data. the back-step (sudden expansion) flow is calculated using wall function approach. The predictions are in reasonable agreement with the experimental data.

Kaul, U. K.↗

NASA NTRS1985

Structural characterization and gas reactions of small metal particles by high-resolution TEM and TED

The interaction of 100 and 200 keV electron beams with amorphous alumina, titania, and aluminum nitride substrates and nanometer-size palladium particulate deposits was investigated for the two extreme cases of (1) large-area electron-beam flash-heating and (2) small-area high-intensity electron-beam irradiation. The former simulates a short-term heating effect with minimum electron irradiation exposure, the latter simulates high-dosage irradiation with minimum heating effect. All alumina and titania samples responded to the flash-heating treatment with significant recrystallization. However, the size, crystal structure, shape, and orientation of the grains depended on the type and thickness of the films and the thickness of the Pd deposit. High-dosage electron irradiation also readily crystallized the alumina substrate films but did not affect the titania films. The alumina recrystallization products were usually either all in the alpha phase, or they were a mixture of small grains in a number of low-temperature phases including gamma, delta, kappa, beta, theta-alumina. Palladium deposits reacted heavily with the alumina substrates during either treatment, but they were very little effected when supported on titania. Both treatments had the same, less prominent localized crystallization effect on aluminum nitride films.

Heinemann, K.↗

NASA NTRS1986

Intersstellar absorption lines between 2000 and 3000 A in nearby stars observed with BUSS

Spectra obtained between 2000 and 3000 A with the Balloon Borne Ultraviolet Spectrophotometer (BUSS) payload were examined for interstellar absorption lines. In bright stars, with spectral types between O9V and F5V, such lines were measured of Mg I, Mg II, Cr II, Mn II, Fe II and Zn II, with Cr II and Zn II data of especially high quality. Column densities were derived and interstellar abundances were determined for the above species. It was found that metal depletion increases with increasing E(B-V); Fe was most affected and Zn showed a small depletion for E(B-V) greater than 0.3 towards Sco-Oph. The metal column densities, derived for Alpha-And, Kappa-Dra, Alpha-Com, Alpha-Aql, and 29 Cyg were used to infer N(H I). It was shown that the ratio of Mg I to Na I is instrumental in determining the ionization structure along each line of sight. The spectra of Aql stars confirms the presence of large gas densities near Alpha-Oph. Moreover, data indicated that the Rho-Oph N(H I) value needs to be altered to 35 x 10 to the 20th/sq cm, based on observed ion ratios and analysis of the Copernicus L-alpha profile.

De Boer, K. S.↗

NASA NTRS1986

Computational simulation of liquid rocket injector anomalies

A computer model has been developed to analyze the three-dimensional two-phase reactive flows in liquid fueled rocket combustors. The model is designed to study the influence of liquid propellant injection nonuniformities on the flow pattern, combustion and heat transfer within the combustor. The Eulerian-Lagrangian approach for simulating polidisperse spray flow, evaporation and combustion has been used. Full coupling between the phases is accounted for. A nonorthogonal, body fitted coordinate system along with a conservative control volume formulation is employed. The physical models built into the model include a kappa-epsilon turbulence model, a two-step chemical reaction, and the six-flux radiation model. Semiempirical models are used to describe all interphase coupling terms as well as chemical reaction rates. The purpose of this study was to demonstrate an analytical capability to predict the effects of reactant injection nonuniformities (injection anomalies) on combustion and heat transfer within the rocket combustion chamber. The results show promising application of the model to comprehensive modeling of liquid propellant rocket engines.

Przekwas, A. J.↗

NASA NTRS1987

Particle-laden swirling free jets: Measurements and predictions

A theoretical and experimental investigation of single-phase and particle-laden weakly swirling jets was conducted. The jets were injected vertically downward from a 19 mm diameter tube with swirl numbers ranging from 0 to 0.33. The particle-laden jets had a single loading ratio (0.2) with particles having a SMD of 39 microns. Mean and fluctuating properties of both phases were measured using nonintrusive laser based methods while particle mass flux was measured using an isokinetic sampling probe. The continuous phase was analyzed using both a baseline kappa-epsilon turbulence model and an extended version with modifications based on the flux Richardson number to account for effects of streamline curvature. To highlight effects of interphase transport rates and particle/turbulence interactions, effects of the particles were analyzed as follows: (1) locally homogeneous flow (LHF) analysis, where interphase transport rates are assumed to be infinitely fast; (2) deterministic separated flow (DSF) analysis, where finite interphase transport rates are considered but particle/turbulence interactions are ignored; and (3) stochastic separated flow (SSF) analysis, where both effects are considered using random-walk computations.

Bulzan, D. L.↗

NASA NTRS1986

Computation of turbulent boundary layer flows with an algebraic stress turbulence model

An algebraic stress turbulence model is presented, characterized by the following: (1) the eddy viscosity expression is derived from the Reynolds stress turbulence model; (2) the turbulent kinetic energy dissipation rate equation is improved by including a production range time scale; and (3) the diffusion coefficients for turbulence equations are adjusted so that the kinetic energy profile extends further into the free stream region found in most experimental data. The turbulent flow equations were solved using a finite element method. Examples include: fully developed channel flow, fully developed pipe flow, flat plate boundary layer flow, plane jet exhausting into a moving stream, circular jet exhausting into a moving stream, and wall jet flow. Computational results compare favorably with experimental data for most of the examples considered. Significantly improved results were obtained for the plane jet flow, the circular jet flow, and the wall jet flow; whereas the remainder are comparable to those obtained by finite difference methods using the standard kappa-epsilon turbulence model. The latter seems to be promising with further improvement of the expression for the eddy viscosity coefficient.

Kim, Sang-Wook↗

NASA NTRS1987

Prediction of recirculation zones in isothermal coaxial jet flows relevant to combustors

The characteristics of the recirculation zones in confined coaxial turbulent jets are investigated numerically employing the kappa - epsilon turbulence model. The geometrical arrangement corresponds to the experimental study of Owen (AIAA J. 1976) and the investigation is undertaken to provide information for isothermal flow relevant to combustor flows. For the first time, the shape, size, and location of the recirculation zones for the above experimental configuration are correctly predicted. The processes leading to the observed results are explained. Detailed comparisons of the prediction with measurements are made. It is shown that the recirculation zones are very sensitive to the central jet exit configuration and the velocity ratio of the jets.

Nallasamy, M.↗

NASA NTRS1987

On the modelling of non-reactive and reactive turbulent combustor flows

A study of non-reactive and reactive axisymmetric combustor flows with and without swirl is presented. Closure of the Reynolds equations is achieved by three models: kappa-epsilon, algebraic stress and Reynolds stress closure. Performance of two locally nonequilibrium and one equilibrium algebraic stress models is analyzed assuming four pressure strain models. A comparison is also made of the performance of a high and a low Reynolds number model for combustor flow calculations using Reynolds stress closures. Effects of diffusion and pressure-strain models on these closures are also investigated. Two models for the scalar transport are presented. One employs the second-moment closure which solves the transport equations for the scalar fluxes, while the other solves the algebraic equations for the scalar fluxes. In addition, two cases of non-premixed and one case of premixed combustion are considered. Fast- and finite-rate chemistry models are applied to non-premixed combustion. Both show promise for application in gas turbine combustors. However, finite rate chemistry models need to be examined to establish a suitable coupling of the heat release effects on turbulence field and rate constants.

Nikjooy, Mohammad↗

NASA NTRS1987

Calculating rotordynamic coefficients of seals by finite-difference techniques

For modelling the turbulent flow in a seal the Navier-Stokes equations in connection with a turbulence (kappa-epsilon) model are solved by a finite-difference method. A motion of the shaft round the centered position is assumed. After calculating the corresponding flow field and the pressure distribution, the rotor-dynamic coefficients of the seal can be determined. These coefficients are compared with results obtained by using the bulk flow theory of Childs and with experimental results.

Dietzen, F. J.↗

NASA NTRS1987

Application of turbulence modeling to predict surface heat transfer in stagnation flow region of circular cylinder

A theoretical analysis and numerical calculations for the turbulent flow field and for the effect of free-stream turbulence on the surface heat transfer rate of a stagnation flow are presented. The emphasis is on the modeling of turbulence and its augmentation of surface heat transfer rate. The flow field considered is the region near the forward stagnation point of a circular cylinder in a uniform turbulent mean flow. The free stream is steady and incompressible with a Reynolds number of the order of 10 to the 5th power and turbulence intensity of less than 5 percent. For this analysis, the flow field is divided into three regions: (1) a uniform free-stream region where the turbulence is homogeneous and isotropic; (2) an external viscid flow region where the turbulence is distorted by the variation of the mean flow velocity; and, (3) an anisotropic turbulent boundary layer region over the cylinder surface. The turbulence modeling techniques used are the kappa-epsilon two-equation model in the external flow region and the time-averaged turbulence transport equation in the boundary layer region. The turbulence double correlations, the mean velocity, and the mean temperature within the boundary layer are solved numerically from the transport equations. The surface heat transfer rate is calculated as functions of the free-stream turbulence longitudinal microlength scale, the turbulence intensity, and the Reynolds number.

Wang, Chi R.↗