The effect of turbulence on mixing in prototype reaction-diffusion systems is analyzed here in the special situation where the turbulence is modeled ideally with two separated scales consisting of a large-scale mean flow plus a small-scale spatiotemporal periodic flow. In the limit of fast reaction and slow diffusion, it is rigorously proved that the turbulence does not contribute to the locati...

A two-dimensional isothermal collisional drift-wave turbulence model including magnetic fluctuations is studied numerically. The model has as limits the electrostatic collisional drift-wave and two-dimensional magnetohydrodynamic systems. The electromagnetic and electrostatic regimes for thermal gradient-driven ~drift-wave! turbulence are decided by the parameter b̂5(4pnT/B)(Ls /Ln ), where Ls a...

Large-eddy simulation (LES) is increasingly used as a tool for studying the dynamics of turbulence in engineering flows. In LES, one explicitly captures the dynamics of the large eddies while modeling the effects of the smaller eddies on the larger ones. Because the statistics of small scale turbulence are expected to be more universal than those of the large scales, LES offers the promise of w...

LA-UR-08-1690 30 Associate Directorate for Theory, Simulation, and Computation (ADTSC) LA-UR-09-01756 Understanding the nature of compressible turbulence is of fundamental importance in many applications ranging from astrophysics to combustion and aerospace engineering. Highly compressible turbulence is now thought to control star formation in dense molecular clouds [1]. The ability to paramete...

Free-surface turbulence, albeit constrained onto a two-dimensional space, exhibits features that barely resemble predictions of simplified two-dimensional modeling. We demonstrate that, in a three-dimensional open channel flow, surface turbulence is characterized by upscale energy transfer, which controls the long-term evolution of the larger scales. We are able to associate downscale and upsca...

in this paper, inflow turbulence effects on the flow wake parameters around a naca0012 airfoil at zero incidence angle and reynolds number of 38,700 were investigated. various turbulence promoter networks were used to achieve turbulence intensity of 5% and 6%. experiments have been conducted for three different turbulence intensities in which mean velocity parameters, turbulence intensity, freq...

This study assesses the sensitivity of numerical results of air flow modelling within an urban environment to the six different turbulence models applied in a specific case of a studied staggered cross-road. The principal parameters investigated in this comparison are position of centres of vortices within a street canyon, two components of the spatial velocity vector, turbulent kinetic energy,...

The possibility of a dynamical core helium Ñash has been studied with two-dimensional hydrodynamic simulations using three separate turbulence models for the treatment of time-dependent convection. Two of these are simple algebraic eddy viscosity models. The third model involves a separate equation for the turbulent kinetic energy density, which then feeds into an expression for the eddy viscos...

The flow field has significantly impact on seeding performance in the suction seeding device. A three-dimensional, incompressible, viscous, RNG turbulence model and the SIMPLE method were used by computational fluid dynamics(CFD), and the flow fields of suction cylinder-seeder with different socket’s radiuses were simulated by Fluent. When vacuum is 4kPa and productivity is 350 trays/h, the sim...

Compressibility may strongly reduce the redistribution of turbulent kinetic energy. The question of how such effects can be taken into account in turbulence models is addressed here. First, a corresponding stochastic turbulence model is developed on the basis of a simplification of the generalized Langevin model for turbulent velocities. This model is then reduced to a deterministic model that ...