Compressibility in turbulent MHD and passive scalar transport: mean-field theory

Abstract

We develop a mean-field theory of compressibility effects in turbulent magnetohydrodynamics and passive scalar transport using the quasi-linear approximation and the spectral $\tau$-approach. We find that compressibility decreases the $\alpha$ effect and the turbulent magnetic diffusivity both at small and large magnetic Reynolds numbers, Rm. Similarly, compressibility decreases the turbulent diffusivity for passive scalars both at small and large Péclet numbers, Pe. On the other hand, compressibility does not affect the effective pumping velocity of the magnetic field for large Rm, but it decreases it for small Rm. Density stratification causes turbulent pumping of passive scalars, but it is found to become weaker with increasing compressibility. No such pumping effect exists for magnetic fields. However, compressibility results in a new passive scalar pumping effect from regions of low to high turbulent intensity both for small and large Péclet numbers. It can be interpreted as compressible turbophoresis of noninertial particles and gaseous admixtures, while the classical turbophoresis effect exists only for inertial particles and causes them to be pumped to regions with lower turbulent intensity.

26 pages, 1 figure, final paper accepted for publication to JPP, jpp.cls

References in corpus (8)

• Mean-field concept and direct numerical simulations of rotating magnetoconvection and the geodynamo
• Laminar and turbulent dynamos in chiral magnetohydrodynamics-I: Theory
• Cosmic ray current-driven turbulence and mean-field dynamo effect
• New scaling for the alpha effect in slowly rotating turbulence
• Turbulent thermal diffusion in a multi-fan turbulence generator with the imposed mean temperature gradient
• Small-scale magnetic buoyancy and magnetic pumping effects in a turbulent convection
• Mean-field theory of differential rotation in density stratified turbulent convection
• Generation of large-scale vorticity in rotating stratified turbulence with inhomogeneous helicity: mean-field theory

Cited by in corpus (14)

• Magnetic field amplification in accretion discs around the first stars: implications for the primordial IMF
• Turbulent viscosity and effective magnetic Prandtl number from simulations of isotropically forced turbulence
• Compressible test-field method and its application to shear dynamos
• Turbulent magnetic helicity fluxes in solar convective zone
• Experimental study of turbulent thermal diffusion of particles in an inhomogeneous forced convective turbulence
• Experimental study of turbulent transport of nanoparticles in convective turbulence
• Experimental study of turbulent thermal diffusion of particles in inhomogeneous and anisotropic turbulence
• Helicity effect on turbulent passive and active scalar diffusivities
• Large-scale clustering of inertial particles in a rotating, stratified and inhomogeneous turbulence
• Compressibility effects in a turbulent transport of temperature field
• Can galactic magnetic fields diffuse into the voids?
• Generation of a large-scale vorticity in a fast rotating density stratified turbulence or turbulent convection
• Experimental investigation of turbulence and turbulent thermal diffusion in strongly inhomogeneous and anisotropic forced convection
• Turbulent transport of radiation in the solar convective zone