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Results for “Effective diffusivity”

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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

On upstream blocking in a viscous diffusive stratified flow

The effect of diffusion of specie upon the flow about a transverse flat plate moving horizontally in a viscous stratified medium is considered. Asymptotic expansions are used to define a parameter regime where a viscous-diffusive-buoyancy balance is dominant. The solution, expressed in terms of an inverse Fourier transform, is numerically integrated. The results show that, as in the non-diffusive problem, a region of closed streamlines exists ahead of the body. However, unlike the case where diffusion is neglected, the density field within this recirculating region is uniquely determined and found to be statically stable. It is also found that varying the relative amount of diffusion affects not only the density distribution, but the velocity profile as well, indicating a strong coupling between the vorticity and specie equation.

Koop, C. G.↗
NASA NTRS1984

The effects of the diffuse radiation fields due to multiple scattering and thermal reradiation by dust on the dynamics and thermodynamics of a dusty cometary atmosphere

A self-consistent model of a dirty, clathrate cometary nucleus is extended to account for diffuse radiation fields caused by multiple scattering and thermal reradiation of the solar continuum by dust. The model is configured to fit conditions expected for the various spacecraft which will encounter Halley's comet at 0.89 AU. The atmosphere is assumed a chemically reactive dust-gas mixture in quasi-steady spherically symmetric expansion. The effect of electron-neutral ion collisions is accounted for, along with rate constants of the various species of clathrate ice particles and radiative transfer of the solar input in the UV, visible and near-IR intervals. The opacity of the circumnuclear dust is projected to be an order of magnitude greater than previous estimates, which severely impacts the potential visibility of the nucleus to the cameras of the flyby satellites.

Marconi, M. L.↗
NASA NTRS1975

Chemical potential effects on neutrino diffusion in supernovae

The validity of imposing a zero chemical potential for neutrinos in hydrodynamic calculations of collapsing supernovae is investigated in the diffusion approximation of neutrino transport. A coupled system of equations is solved for neutrino and energy diffusion fluxes as well as lepton diffusion in a collapsing supernovae ambient medium, and the results indicate a substantial growth in the neutrino chemical potential for densities greater than 10 to the 12th power gm/cu cm. The rate of energy transport is shown to be significantly affected by increases in Fermi integrals and chemical-potential gradients accompanied by decreases in temperature, and the extent of neutrino particle/antiparticle reactions is found also to affect energy diffusion rates. It is concluded that the photon-like behavior usually assumed for neutrinos may be incorrect and that an extension of the Sn transport approximation to include lepton characteristics is necessary for a definitive answer to the question of neutrino transport in supernovae.

Mazurek, T. J.↗
NASA NTRS1975

A preliminary study of the effects of vortex diffusers (winglets) on wing flutter

Some experimental flutter results are presented for a simple, flat-plate wing model and for the same wing model equipped with two different upper surface vortex diffusers over the Mach number range from about 0.70 to 0.95. Both vortex diffusers had the same planform, but one weighed about 0.3 percent of the basic wing weight, whereas the other weighed about 1.8 percent of the wing weight. The addition of the lighter vortex diffuser reduced the flutter dynamic pressure by about 3 percent; the heavier vortex diffuser reduced the flutter dynamic pressure by about 12 percent. The experimental flutter results are compared at a Mach number of 0.80 with analytical flutter results obtained by using doublet lattice and lifting surface (Kernel function) unsteady aerodynamic theories.

Doggett, R. V., Jr.↗
NASA NTRS1976

High-beta effects and anomalous diffusion in plasmas expanding into magnetic fields

A metallic laser-produced plasma is allowed to expand transversely into an applied magnetic field, under conditions where the typical ion cyclotron radius is much larger, and the electron cyclotron radius much smaller, than the experimental dimensions. A stationary background plasma may also be present. Initially, the flow energy density exceeds (B squared/8 times pi), where B is the ambient magnetic field. Magnetic coil probes, Langmuir probes, and microwave diagnostics are used to study the plasma-field interaction. Field compression at the leading edge and field exclusion within the expanding plasma are seen. The diagnostic measurements and comparison with a theoretical model demonstrate plasma turbulence and anomalously high diffusion of field into the expanding plasma.

Koopman, D. W.↗
NASA NTRS1978

Effect of diffusion-thermal processes on the high-latitude topside ionosphere

The extent to which diffusion-thermal heat flow affects H(+) temperatures in the high-latitude topside ionosphere is studied. Such a heat flow occurs whenever there are H(+)-O(+) relative drifts. From our study we have found that at high-latitudes, where H(+) flows up and out of the topside ionosphere, diffusion-thermal heat flow acts to reduce H(+) temperatures by 500-600 K at altitudes above about 900 km.

Schunk, R. W.↗
NASA NTRS1983

Effects of interstage diffuser flow distortion on the performance of a 15.41-centimeter tip diameter axial power turbine

The performance of a variable-area stator, axial flow power turbine was determined in a cold-air component research rig for two inlet duct configurations. The two ducts were an interstage diffuser duct and an accelerated-flow inlet duct which produced stator inlet boundary layer flow blockages of 11 percent and 3 percent, respectively. Turbine blade total efficiency at design point was measured to be 5.3 percent greater with the accelerated-flow inlet duct installed due to the reduction in inlet blockage. Blade component measurements show that of this performance improvement, 35 percent occurred in the stator and 65 percent occurred in the rotor. Analysis of inlet duct internal flow using an Axisymmetric Diffuser Duct Code (ADD Code) were in substantial agreement with the test data.

Mclallin, K. L.↗
NASA NTRS1983

Effects of interstage diffuser flow distortion on the performance of a 15.41-centimeter tip diameter axial power turbine

The performance of a variable-area stator, axial flow power turbine was determined in a cold-air component research rig for two inlet duct configurations. The two ducts were an interstage diffuser duct and an accelerated-flow inlet duct which produced stator inlet boundary layer flow blockages of 11 percent and 3 percent, respectively. Turbine blade total efficiency at design point was measured to be 5.3 percent greater with the accelerated-flow inlet duct installed due to the reduction in inlet blockage. Blade component measurements show that of this performance improvement, 35 percent occurred in the stator and 65 percent occurred in the rotor. Analysis of inlet duct internal flow using an Axisymmetric Diffuser Duct Code (ADD Code) were in substantial agreement with the test data.

Mclallin, K. L.↗
NASA NTRS1994

Effects of Refractive Index and Diffuse or Specular Boundaries on a Radiating Isothermal Layer

Equilibrium temperatures of an absorbing-emitting layer were obtained for exposure to incident radiation and with the layer boundaries either specular or diffuse. For high refractive indices the surface condition can influence the radiative heat balance if the layer optical thickness is small. Hence for a spectrally varying absorption coefficient the layer temperature is affected if there is significant radiative energy in the spectral range with a small absorption coefficient. Similar behavior was obtained for transient radiative cooling of a layer where the results are affected by the initial temperature and hence the fraction of energy radiated in the short wavelength region where the absorption coefficient is small. The results are a layer without internal scattering. If internal scattering is significant, the radiation reaching the internal surface of a boundary is diffused and the effect of the two different surface conditions would become small.

Siegel, R.↗
NASA NTRS1992

Effects of g-jitter and cross-diffusion on the onset of convection in doubly diffusive systems

The effects of a modulated gravity field in doubly diffusive layers with and without cross-diffusion are studied. Attention is focused on the determination of linear stability criteria for such systems. Floquet theory is used to establish the stability criteria by a systematic analysis of the topology of the neutral curves from which stability boundaries can be constructed. Convective stability boundaries for gravity-modulated doubly cross-diffusive systems are presented for the cases of dynamically free and rigid boundaries. Two physically different forms of layer stratification are considered: (1) imposed independent gradients of two components and (2) a solute gradient induced by a fixed temperature gradient.

Terrones, Guillermo↗