Effective mass and energy fluxes in strongly compressible magnetohydrodynamic turbulence: Density-variance and compressive cross-helicity effects
Abstract
Strongly compressible magnetohydrodynamic (MHD) turbulence is investigated with the aid of the multiple-scale direct-interaction approximation; a renormalized perturbation closure scheme for inhomogeneous turbulence at very high Reynolds numbers. The turbulent mass flux <{ρ{u}}> and the turbulent internal-energy flux <{q'{u}}> are evaluated with analytical expressions of the turbulent transport coefficients. It is shown that, in addition to the usual gradient-diffusion terms, which arise even in the solenoidal case, (i) the density-variance effect in the cross-diffusion terms and (ii) the compressive cross-helicity effect in the flux along the mean magnetic field show up as genuine compressibility effects. Turbulence modelling based on those theoretical results is also presented. The relationship of these effect with the magnetohydrodynamic waves (torsional Alfven wave and magnetoacoustic waves) is also argued. These analyses provide a firm basis for a turbulence model that deviates from the usual gradient-diffusion approximation, and pave the way for turbulence modelling beyond the heuristic modelling. Some possible applications to shock-turbulence interaction in the context of dynamo and magnetic reconnection are also discussed.
References Yokoi, N. "Cross helicity and related dynamo," Geophys. Astrophys. Fluid Dyn. 110, 114-184 (2013) doi.org/10.1080/03091929.2012.754022 Yokoi, N. "Electromotive force in strongly compressible magnetohydrodynamic turbulence," J. Plasma Phys. 84, 1-26 (2018) doi:10.1017/S0022377818000727- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMNG23A..05Y
- Keywords:
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- 3315 Data assimilation;
- ATMOSPHERIC PROCESSESDE: 1910 Data assimilation;
- integration and fusion;
- INFORMATICSDE: 3275 Uncertainty quantification;
- MATHEMATICAL GEOPHYSICSDE: 4468 Probability distributions;
- heavy and fat-tailed;
- NONLINEAR GEOPHYSICS