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Mitchell C Begelman - One of the best experts on this subject based on the ideXlab platform.

  • entropy production in relativistic Jet Boundary layers
    Monthly Notices of the Royal Astronomical Society, 2015
    Co-Authors: Susanna Kohler, Mitchell C Begelman
    Abstract:

    Hot relativistic Jets, passing through a background medium with a pressure gradient p \propto r^{-\eta} where 2 < \eta <= 8/3, develop a shocked Boundary layer containing a significant fraction of the Jet power. In previous work, we developed a self-similar description of the Boundary layer assuming isentropic flow, but we found that such models respect global energy conservation only for the special case \eta = 8/3. Here we demonstrate that models with \eta < 8/3 can be made self-consistent if we relax the assumption of constant specific entropy. Instead, the entropy must increase with increasing r along the Boundary layer, presumably due to multiple shocks driven into the flow as it gradually collimates. The increase in specific entropy slows the acceleration rate of the flow and provides a source of internal energy that could be channeled into radiation. We suggest that this process may be important for determining the radiative characteristics of tidal disruption events and gamma-ray bursts from collapsars.

Guang Yang - One of the best experts on this subject based on the ideXlab platform.

  • large eddy simulation and experimental study of turbulent mixed convection inside a cavity with large rayleigh number effect of buoyancy
    Building and Environment, 2019
    Co-Authors: Yiye Huang, Guang Yang
    Abstract:

    Abstract Turbulent mixed convection characteristics inside a rectangular cavity are studied experimentally and numerically. Hot wire anemometry (HWA), particle image velocimetry (PIV) and thermocouples were used to study the velocity and temperature field for Re = 8.3 × 103 and Ra = 4.34 × 1012. The Large Eddy Simulation (LES) was carried out using the dynamic Smagorinsky model and the Favre-averaging method for 1.08 × 1012 ≤ Ra ≤ 6.50 × 1012 to further investigate the effect of the buoyancy. The time-averaged field demonstrates the circulation flow structure and thermal stratification in the cavity. The heat transfer on the heated side wall shows a significant deviation from natural convection due to the center Jet flow. The turbulent flow development and coherent structures induced by buoyancy and shear force are presented with the second invariant of the velocity gradient tensor. The turbulence quantities such as velocity and temperature fluctuation, and turbulent heat flux are found highly concentrated near the heated side walls and the center Jet Boundary, and increase significantly with buoyancy. By comparing the experimental results, the accuracy of the LES for mixed convection is also determined.

Susanna Kohler - One of the best experts on this subject based on the ideXlab platform.

  • entropy production in relativistic Jet Boundary layers
    Monthly Notices of the Royal Astronomical Society, 2015
    Co-Authors: Susanna Kohler, Mitchell C Begelman
    Abstract:

    Hot relativistic Jets, passing through a background medium with a pressure gradient p \propto r^{-\eta} where 2 < \eta <= 8/3, develop a shocked Boundary layer containing a significant fraction of the Jet power. In previous work, we developed a self-similar description of the Boundary layer assuming isentropic flow, but we found that such models respect global energy conservation only for the special case \eta = 8/3. Here we demonstrate that models with \eta < 8/3 can be made self-consistent if we relax the assumption of constant specific entropy. Instead, the entropy must increase with increasing r along the Boundary layer, presumably due to multiple shocks driven into the flow as it gradually collimates. The increase in specific entropy slows the acceleration rate of the flow and provides a source of internal energy that could be channeled into radiation. We suggest that this process may be important for determining the radiative characteristics of tidal disruption events and gamma-ray bursts from collapsars.

Alex Klimas - One of the best experts on this subject based on the ideXlab platform.

  • scaling of the anomalous boost in relativistic Jet Boundary layer
    The Astrophysical Journal, 2010
    Co-Authors: Seiji Zenitani, M Hesse, Alex Klimas
    Abstract:

    We investigate the one-dimensional interaction of a relativistic Jet and an external medium. Relativistic magnetohydrodynamic simulations show an anomalous boost of the Jet fluid in the Boundary layer, as previously reported. We describe the boost mechanism using an ideal relativistic fluid and magnetohydrodynamic theory. The kinetic model is also examined for further understanding. Simple scaling laws for the maximum Lorentz factor are derived, and verified by the simulations.

Mark P Wernet - One of the best experts on this subject based on the ideXlab platform.

  • an experimental study of the oscillatory flow structure of tone producing supersonic impinging Jets
    Journal of Fluid Mechanics, 2005
    Co-Authors: Brenda Henderson, James Bridges, Mark P Wernet
    Abstract:

    An experimental investigation into the structure of a supersonic Jet impinging on a large plate is presented. Digital particle image velocimetry (DPIV), shadowgraph photography and acoustic measurements are used to understand the relationship between the unsteady Jet structure and the production of tones for nozzle-to-plate spacings between 1 and 5 nozzle exit diameters at a nozzle–pressure ratio equal to 4. Results indicate that the instability of the Jet depends on the location of the plate in the shock cell structure of the corresponding free Jet and the strength of the standoff shock wave, rather than on the occurrence of recirculation zones in the impingement region. Phase-locked studies show streamwise displacements of the stand-off shock wave, a moving recirculation zone in the subsonic flow in front of the plate, and significant oscillations of both the compression and expansion regions in the peripheral supersonic flow when tones are produced. Sound is shown to be generated by periodic pulsing of the wall Jet Boundary resulting from periodic motion of the flow in the impingement and near-wall regions of the flow.