RESUMEN
The aim of this letter is to assess existing theories for Rayleigh-Taylor small turbulent scales. For this purpose, we propose to adapt the Monin-Yaglom relation to the Rayleigh-Taylor turbulence context. A special emphasis is put on the inhomogeneity of the flow and on the effect of buoyancy forces. This relation is then used to show that, among existing theories, the standard Kolmogorov-Obukhov theory should apply to Rayleigh-Taylor turbulence in the limit of a large Reynolds number, large times, and small scales.
RESUMEN
The purpose of this work is to derive a small turbulent Péclet-small turbulent Mach number approximation for hydroradiative turbulent mixing zones encountered in stellar interiors where the radiative conductivity can overwhelms the turbulent transport. To this end, we proceed to an asymptotic analysis and determine orders of magnitude for the fluctuating temperature and pressure, as well as closed expressions for the fluctuating conduction and velocity divergence. The latter is used to extend a Reynolds stress model to the small-Péclet regime. Three-dimensional direct numerical simulations of radiative Rayleigh-Taylor turbulent mixing zones are performed, first, to validate the asymptotic predictions and, second, to validate their use in the Reynolds stress model.
RESUMEN
Light is shed upon Eulerian Monte Carlo methods and their application to the simulation of turbulent reactive flows. A rapid decorrelating velocity-field model is used to derive stochastic partial differential equations (SPDE's) stochastically equivalent to the modeled one-point joint probability density function of turbulent reactive scalars. Those SPDE's are shown to be hyperbolic, advection-reaction equations. They are dealt with in a generalized sense, so that discontinuities in the scalar fields can be treated. A numerical analysis is proposed and numerical tests are carried out. In particular, a comparison with the Lagrangian Monte Carlo method is performed.
RESUMEN
In this work, a pseudocompressible approximation relevant for turbulent mixing flows encountered in shock tubes is derived. The asymptotic analysis used for this purpose puts forward the role played by four dimensionless numbers on the flow compressibility, namely, the turbulent, deformation, stratification, and buoyancy force Mach numbers. The existence of rapid distortion and diffusion-dissipation regimes is also accounted for in the analysis. Some consequences of the derived pseudocompressible approximation on statistical turbulence models are discussed. In particular, the evolutions of the density variance and flux are examined, as well as the turbulent transport of energy. The different aspects of this study are assessed by performing a direct numerical simulation of a shock tube flow configuration.