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  • Other Sources  (3)
  • Inorganic and Physical Chemistry  (2)
  • Fluid Mechanics and Thermodynamics  (1)
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  • 1
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    Effects of Gravity on Sheared and Nonsheared Turbulent Nonpremixed Flames (1997)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The present numerical study is concerned with the fundamental physics of the multi-way interaction between turbulence, chemical reaction and buoyancy in a nonpremixed flame. The method of direct numerical simulation (DNS) is used to solve the instantaneous three-dimensional governing equations (continuity, Navier-Stokes, species mass fractions and energy) under the zero-Mach number assumption. Because of the present supercomputer limitations, we consider two simple flow geometries, namely an initially uniform flow without shear (equivalent to grid-generated turbulence) and an initially uniform shear flow. In each flow, the fuel and oxidant initially exist as two separate streams. As the reactants mix, chemical reaction takes place and exothermic energy is released causing variations in density. In the presence of a gravity field, the spatial and temporal distributions of the induced buoyancy forces depend on the local density gradients and the direction of the gravitational acceleration.
    Keywords: Inorganic and Physical Chemistry
    Type: Fourth International Microgravity Combustion Workshop; 173-178; NASA-CP-10194
    Format: text
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  • 2
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    Method for Trace Oxygen Detection (1997)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Trace levels of molecular oxygen are measured by introducing a gas containing the molecular oxygen into a target zone, and impacting the molecular oxygen in the target zone with electrons at the O(-) resonant energy level for dissociative electron attachment to produce O(-) ions. Preferably, the electrons have an energy of about 4 to about 10 eV. The amount of O(-) ions produced is measured, and is correlated with the molecular oxygen content in the target zone. The technique is effective for measuring levels of oxygen below 50 ppb. and even less than 1 ppb. The amount of O(-) can be measured in a quadrupole mass analyzer. Best results are obtained when the electrons have an energy of about 6 to about 8 eV. and preferably about 6.8 eV. The method can be used for other species by selecting the appropriate electron energy level.
    Keywords: Inorganic and Physical Chemistry
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Effects of Gravity on Sheared Turbulence Laden with Bubbles or Droplets (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: The objective of this numerical/experimental study is to improve the understanding of the effects of gravity on the two-way interaction between dispersed particles (bubbles or liquid droplets) and the carrier turbulent flow. The first phase of the project considers isotropic turbulence. Turbulent homogeneous shear flows laden with droplets/bubbles will be studied in the next phase. The experiments reported here are concerned with the dispersion of liquid droplets by homogeneous turbulence under various gravitational conditions and the effect of these droplets on the evolution of the turbulence of the carrier fluid (air). Direct numerical simulations (DNS) of bubble - laden isotropic decaying turbulence are performed using the two-fluid approach (TF) instead of the Eulerian-Lagrangian approach (EL). The motivation for using the TF formulation is that EL requires considerable computational resources especially for the case of two-way coupling where the instantaneous trajectories of a large number of individual bubbles need to be computed. The TF formulation is developed by spatially averaging the instantaneous equations of the carrier flow and bubble phase over a scale of the order of the Kolmogorov length scale which, in our case, is much larger than the bubble diameter. On that scale, the bubbles are treated as a continuum (without molecular diffusivity) characterized by the bubble phase velocity field and concentration (volume fraction). The bubble concentration, C, is assumed small enough to neglect the bubble-bubble interactions.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: Proceedings of the Fourth Microgravity Fluid Physics and Transport Phenomena Conference; 454-459; NASA/CP-1999-208526/SUPPL1
    Format: application/pdf
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