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https://stockholmuniversity.zoom.us/j/530682073
Compressibility effects in a turbulent transport of temperature, particles and magnetic field are discussed. Compressibility of fluid flow when Mach number is not small decreases the alpha effect and the turbulent magnetic diffusivity both at small and large magnetic Reynolds numbers, Rm. Similarly, compressibility decreases the turbulent diffusivity particle number density both at small and large Peclet numbers, Pe. Compressibility of a fluid flow reduces the turbulent diffusivity of the mean temperature field similarly to that for particle number density and magnetic field. However, expression for turbulent diffusion coefficient for the mean temperature field in a compressible turbulence is different from those for particle number density and magnetic field. Compressibility does not affect the turbulent pumping velocity of the magnetic field for large Rm, but it decreases it for small Rm. Density stratification causes turbulent pumping of particle number density to the regions with the maximum fluid density, but this effect becomes weaker with increasing compressibility. No such pumping effect exists for magnetic fields. Compressibility of fluid flow when Mach number is not small results in a new pumping effect of particle number density from regions of low to high turbulent intensity both for small and large Peclet numbers. This effect can be interpreted as compressible turbophoresis of non-inertial 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. Combined effect of compressibility and inhomogeneity of turbulence causes an increase of the mean temperature in the regions with more intense velocity fluctuations due to a turbulent pumping. Formally, this effect is similar to a phenomenon of compressible turbophoresis for non-inertial particles or gaseous admixtures. Gradient of the mean fluid pressure results in an additional turbulent pumping of the mean temperature field. The latter effect is similar to turbulent barodiffusion of particles and gaseous admixtures. Compressibility of a fluid flow when Mach number is not small also causes a turbulent cooling of the surrounding fluid due to an additional sink term in the equation for the mean temperature field. There is no analog of this effect for particles.