We present results from a systematic numerical study of decaying turbulence in a dilute polymer solution by using a shell-model version of the finitely extensible nonlinear elastic and Peterlin equations. Our study leads to an appealing definition of the drag reduction for the case of decaying turbulence. We exhibit several new results, such as the potential-energy spectrum of the polymer, hith...

Large-eddy simulation (LES) is used to investigate turbulence in a marginally-unstable stratified shear layer motivated by the observation of deep-cycle turbulence in the upper Equatorial Undercurrents. The initial condition consists of uniform shear and stratification profiles, and a constant gradient Richardson number Rig = 0.25. A constant wind stress forces turbulence in the upper surface l...

Accurate CFD simulation of coupled outdoor wind flow and indoor air flow is essential for the design and evaluation of natural cross-ventilation strategies for buildings. It is widely recognized that CFD simulations can be very sensitive to the large number of computational parameters that have to be set by the user. Therefore, detailed and generic sensitivity analyses of the impact of these pa...

Large-eddy simulations described here have included the effect of canopy drag through the depth of a plant canopy. Specifically, we have considered the simulation of flow through a forest. Drag forces enter the simulation with the inclusion of form and viscous drag forces in the momentum equation. In addition, we have carried a variable to represent the kinetic energy (KE) associated with the t...

Aquatic plants convert mean kinetic energy into turbulent kinetic energy at the scale of the plant stems and branches. This energy transfer, linked to wake generation, affects vegetative drag and turbulence intensity. Drawing on this physical link, a model is developed to describe the drag, turbulence and diffusion for flow through emergent vegetation which for the first time captures the relev...

In this paper, we derive a general relationship for the turbulent Prandtl number Pr t for homogeneous stably stratified turbulence from the turbulent kinetic energy and scalar variance equations. A formulation for the turbulent Prandtl number, Pr t , is developed in terms of a mixing length scale LM and an overturning length scale LE , the ratio of the mechanical (turbulent kinetic energy) deca...

Plasma turbulence consists of an ensemble of enhanced, broadband electromagnetic fluctuations, typically driven by multi-wave interactions which transfer energy in wavevector space via non- linear cascade processes. Temperature anisotropy instabilities in collisionless plasmas are driven by quasi-linear wave-particle interactions which transfer particle kinetic energy to field fluctuation energ...

The decay of kinetic helicity is studied in numerical models of forced turbulence using either an externally imposed forcing function as an inhomogeneous term in the equations or, alternatively, a term linear in the velocity giving rise to a linear instability. The externally imposed forcing function injects energy at the largest scales, giving rise to a turbulent inertial range with nearly con...

We compute 3D models of supersonic, sub-Alfv enic, and super-Alfv enic decaying turbulence, with initial rms Alfv en and Mach numbers ranging up to ve, and an isothermal equation of state appropriate for star-forming interstellar clouds of molecular gas. We nd that in 3D the kinetic energy decays as t ? , with 0:85 < < 1:2. In 1D magnetized turbulence actually decays faster than unmagnetized tu...

The modulation of isotropic turbulence by particles has been investigated using direct numerical simulation (DNS). The particular focus of the present work is on the class of dilute flows in which particle volume fractions and inter-particle collisions are negligible. Gravitational settling is also neglected and particle motion is assumed to be governed by drag with particle relaxation times ra...