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  • Other Sources  (2)
  • Earth Resources and Remote Sensing  (1)
  • FLUID MECHANICS AND HEAT TRANSFER  (1)
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  • Other Sources  (2)
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  • 1
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    Low Mach number two-dimensional hydrodynamic turbulence - Energy budgets and density fluctuations in a polytropic fluid (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Theory suggests that three distinct types of turbulence can occur in the low Mach number limit of polytropic flow: nearly incompressible flows dominated by vorticity, nearly pure acoustic turbulence dominated by compression, and flows characterized by near statistical equipartition of vorticity and compressions. Distinctions between these kinds of turbulence are investigated here by direct numerical simulation of two-dimensional compressible hydrodynamic turbulence. Dynamical scalings of density fluctuations, examination of the ratio of transverse to longitudinal velocity fluctuations, and spectral decomposition of the fluctuations are employed to distinguish the nature of these low Mach number solutions. A strong dependence on the initial data is observed, as well as a tendency for enhanced effects of compressibility at later times and at higher wave numbers, as suggested by theories of nearly incompressible flows.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 4; 148-164
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    The Development of Kolmogoroff-Like Power Spectra in the Expanding Solar Wind (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: Power spectra of the solar wind fluctuations consistently exhibit a -5/3 power-law slope consistent with the idea that the medium is undergoing a turbulent cascade as seen in ordinary fluids. This is surprising both because the radial streams and the magnetic field threading the plasma will induce anisotropies and because the expansion of the wind will tend to lead to the suppression of nonlinear cascades. These conditions violate the assumptions used by Kolmogoroff to derive the -5/3 law. We have studied this issue using a compressible IMHD code in spherical coordinates and have shown that a -5/3 spectrum results from a broad-band flat-spectrum input condition that is sheared and distorted by a current sheet as the wind expands. We determine spectra from time series taken at selected points in the domain as is done with observational spacecraft data. The spectra are very like those we have seen in nonexpanding runs and exhibit evolution and compressive characteristics very similar to those seen in observations. We will report on these results in addition to a new set of runs intended to constrain the necessary and sufficient conditions for the spectra to have this form. The simulation also allows us to examine the anisotropy for the spectra to attempt to determine why the result of an isotropic magnetofluid is obtained in a highly anisotropic situation.
    Keywords: Earth Resources and Remote Sensing
    Type: Solar Wind 9; Oct 05, 1998 - Oct 09, 1998; Nantucket, RI; United States
    Format: text
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    NASA TECHNICAL REPORTS
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