Context. The standard dynamo model for the solar and stellar magnetic fields is based on the αΩ mechanism, namely, an interplay between differential rotation (the Ω effect) and a mean electromotive force generated by helical turbulent convection flows (the α effect). There are, however, a number of problems with the α effect and αΩ dynamo models. Two of them are that, in the case of the Sun, th...

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Using numerical methods, we systematically study in the framework of ideal MHD the effect of magnetic fields on heat transfer within a turbulent gas. We measure the rates of passive scalar diffusion within magnetized fluids and make the comparisons a) between MHD and hydro simulations, b) between different MHD runs with different values of the external magnetic field (up to the energy equiparti...

We investigate the enstrophy dynamics in relation to objective Eulerian coherent structures (OECSs) and their impact on scalar transport near turbulent/non-turbulent interface (TNTI) flows with without stable stratification. confirm that vortex-stretching produces inside boundaries of OECSs, while viscous diffusion transfers across structures. Although often overlooked literature, dissipation w...

Direct two-dimensional numerical simulation and experiments, in which small rocket motors accelerate a tank containing two fluids, have been used to investigate turbulent mixing by Rayleigh-Taylor instability at a wide range of density ratios. The experimental data obtained so far has been used to calibrate an empirical model of the mixing process which is needed to make predictions for complex...

Recent experimental investigations of combustion in diesel engines showed that the initial premix burn creates pockets of soot and fuel that must burn out in a diffusion-flame mode in order to complete the combustion [5, 6]. Understanding the final stages of this process is critical to predicting the emissions of soot and NOx. This effort uses numerical simulations to investigate burnout of dif...

The scalar structure of the overfire (fuel-lean) region of sooting turbulent diffusion flames was investigated, considering ethylene and acetylene burning in air. Measurements and predictions are reported of the mean concentrations of major gas species and mean soot volume fractions. Predictions were based on the conserved-scaiar formalism in conjunction with the laminar flamelet approximation....

We discuss hydrostatic models of galaxy clusters in which heat diffusion balances radiative cooling. We consider two different sources of diffusion, thermal conduction and turbulent mixing, parameterized by dimensionless coefficients, f and αmix, respectively. Models with thermal conduction give reasonably good fits to the density and temperature profiles of several cooling flow clusters, but s...

The magnetic Prandtl number PrM is the ratio of viscosity to resistivity. In astrophysical disks the diffusion of angular momentum (viscosity) and magnetic fields (resistivity) are controlled by turbulence. Phenomenological models of the evolution of large scale poloidal magnetic fields in disks suggest that the turbulent magnetic Prandtl number PrM,T controls the rate of escape of vertical fie...

The single-particle dispersion, Lagrangian structure functions and Lagrangian energy spectra characteristic of two-dimensional incompressible turbulent flows are investigated theoretically and numerically. The domain of validity of the classical asymptotic estimates is extended; it is shown in particular that the asymptotic behavior of the single-particle dispersion at small times remains valid...