A subgrid model is developed and applied to a large-eddy simulation of the Kolmogorov inertial subrange. Currently popular models are derived from turbulent energy equation, resulting in significant loss information as consequence statistical averaging performed going Navier–Stokes equation equation. The here based directly on improved contains two terms: an eddy viscosity stochastic force. These terms computed EDQNM representation momentum fully resolved direct numerical simulation. Use...

Forced rotating turbulence is simulated within a periodic box of small aspect ratio. Critical parameter values are found for the stability 2D inverse cascade energy in presence 3D motions at scales. There critical rotation rate below which forcing leads to an equilibrated state, while slightly larger rate, drives cascade. It shown that and forward cascades can coexist. This study relevant geophysical flows, contains physics beyond scope quasigeostrophic models.

Four species in the ELEGANS group of subgenus Caenorhabditis are distinguished by two very different mating systems: androdioecy C. elegans and briggsae with males self-fertilizing hermaphrodites dioecy remanei sp. strain CB5161 females. Using chemotaxis assays, we demonstrate that females secrete a potent sex pheromone attracts from distance, whereas do not. The female is not species-specific, all four attracted to both pheromones. is, however, sex-specific, only secreting attracting males....

Abstract The free-living nematode worm Caenorhabditis elegans reproduces primarily as a self-fertilizing hermaphrodite, yet males are maintained in wild-type populations at low frequency. To determine the role of C. elegans, we develop mathematical model for genetic system hermaphrodites that can either self-fertilize or be fertilized by and perform laboratory observations experiments on both related dioecious species remanei. We show mating efficiency is poor compared to more attracted...

Direct numerical simulations of decaying two-dimensional turbulence in a fluid large extent are performed primarily to ascertain the asymptotic decay laws energy and enstrophy. It is determined that critical Reynolds number Rc exists such for initial numbers with R(0)<Rc final period solutions result, whereas R(0)>Rc flow field evolves increasing number. Exactly at R(0)=Rc, constant decays as t−1 enstrophy t−2. A t−2 law was originally predicted by Batchelor [Phys. Fluids...

We consider the statistically homogeneous motion that is generated by buoyancy forces after creation of random fluctuations in density infinite fluid at an initial instant. The mean uniform, and are smoothed molecular diffusion. This turbulent flow system has interesting properties, shows how self-generated contributes to rate mixing 'active' scalar contaminant.If nonlinear terms governing equations negligible, there exact solution which history depends crucially on form spectrum near zero...

By simple analytical and large-eddy simulations, the time evolution of kinetic energy scalar variance in decaying isotropic turbulence transporting passive scalars are determined. The a field with without uniform mean gradient is considered. First, similarity states flow during final period decay discussed. Exact solutions may be obtained, these depend only on form scalar-variance spectra at low wave numbers, molecular transport coefficients. for mean-scalar special interest, we find that...

The evolutionary maintenance of sexual reproduction remains a controversial problem. It was recently shown that recessive deleterious mutations create differences in the mutation load vs. asexual populations. Here we show low levels population structure or inbreeding can greatly enhance importance context With structure, cost sex be substantially reduced even eliminated for realistic dominance.

Abstract A leading hypothesis for the evolutionary function of sex postulates that is an adaptation purges deleterious mutations from genome, thereby increasing equilibrium mean fitness a sexual population relative to its asexual competitor. This requires two necessary conditions: first, mutation rate per genome must be order one, and, second, multiple within act with positive epistasis, is, or more different genes harmful together than if they acted independently. Here, by reconsidering...

Although the nematode worm Caenorhabditis elegans reproduces primarily as a self-fertilizing hermaphrodite, males are maintained in natural populations at low frequency. In this commentary, I discuss evolutionary forces that maintain and role might play mating system.

A model for stationary, fully developed turbulence is presented. The physical used to describe the nonlinear interactions provides an equation turbulent spectral energy function F(k) as a of time scale fed into system, n−1s. makes quantitative predictions that are compared with following available data different nature. (a) For convection, in case constant superadiabatic gradient and σ≪1 (σ≡Prandtl number), convective flux computed result mixing length theory (MLT). variable gradient,...

The decay of a homogeneous turbulence generated by an axisymmetric distribution random impulsive forces acting at the initial instant is studied means large-eddy simulations. may be either parallel or perpendicular to symmetry axis. For forces, which result in k4 low wave number energy spectrum turbulence, it determined that flow approaches isotropy on all scales motion long times, provided Reynolds large. However, for type originally proposed Saffman [J. Fluid Mech. 27, 581 (1967)], k2...

The time evolution of the Loitsianski integral at high-Reynolds numbers is determined by computing an ensemble average a large number independent large-eddy simulations decaying isotropic turbulence. It found that becomes proportional to tγ times and γ ≊0.25. present illustrate efficient use massively parallel computers for simulating ensembles turbulent flows.

The spectrum of a passive temperature field, G(k), has been determined by numerical simulation using three kinds isotropic turbulent velocity fields. For time independent and Gaussian the resulting G(k) form G(k)=G0εθε2/3 χ−3k−17/3, with G0=0.33±0.02 Ko, confirming prediction Batchelor, Howells, Townsend [J. Fluid Mech. 5, 134 (1959)]. field developed through Navier–Stokes equations then frozen in time, same as above, but G0 =0.39±0.03 Ko. Finally, for concurrently collapses onto obtained...

An infinite fluid with a vertical cubic temperature profile in the absence of motion is considered as model for penetrative convection which central unstably stratified layer bounded above and below by stably layers. Turbulence statistics from direct large eddy numerical simulations mean gradient, velocity variances heat flux are presented Rayleigh numbers R up to four orders magnitude critical. By means simplified second-moment closure, analytical scaling laws determined. For high numbers,...

The similarity form of the scalar-variance spectrum at high Schmidt numbers is investigated for nonstationary turbulence. Theoretical arguments show that Batchelor scaling may apply only Reynolds numbers. At low numbers, Batchlor not possible unless turbulence stationary or enstrophy decays asymptotically as t−2. When this latter condition satisfied, it shown from an analysis using both and Kraichnan models transfer k−1 power law in viscous-convective subrange modified. Results direct...

The inertial–conductive subrange spectrum of a passive temperature field fluid small Prandtl number is determined by large-eddy simulation. Results for simulations both freely decaying and forced turbulence are presented. In the turbulence, subgrid model used to simulate turbulent velocity with k−5/3 inertial energy convecting eight different fields well-resolved conductive subranges. again an field; however, now at lowest wave numbers simulation, external uniform mean gradient imposed....

The decay of high-Reynolds-number inhomogeneous turbulence in an unbounded domain is considered. may be initially localized one to three spatial directions and the fluid assumed at rest infinity those directions. Previous arguments used determine laws homogeneous are extended by integrating statistics over Dimensional based on invariance or near-invariance low-wavenumber spectral coefficients associated with integrated mean-square velocity asymptotic for turbulence. These depend number flow...

In this paper, we apply two theoretical turbulence models, DIA and the recent GISS model, to study properties of a turbulent channel flow. Both models provide kinetic energy spectral function E(k) as solution nonlinear equation; employ same source but different closures. The is characterized by rate n s ( k ) which derived from complex eigenvalues Orr–Sommerfeld equation in basic flow taken be Poiseuille type. solved for variety Reynolds numbers corresponding available experimental data. A...