The normalized turbulent dissipation rate Cϵ is studied in decaying and forced turbulence by direct numerical simulations, large-eddy closure calculations. A large difference the values of observed for two types turbulence. This found at moderate Reynolds number, it shown that persists high where value becomes independent but still not unique. can be explained influence nonlinear cascade time introduces a spectral disequilibrium statistically nonstationary Phenomenological analysis yields...

Generating laboratory flows resembling atmospheric turbulence is of prime importance to study the effect wind fluctuations on objects such as buildings, vehicles, or turbines. A novel driving an active grid following a stochastic process used generate velocity with correlation lengths, and, thus, integral scales, much larger than transverse dimension tunnel. The combined action and modulation fan speed allows one flow characterized by four-decade inertial range scale Reynolds number...

Recent experiments and simulations have shown that unsteady turbulent flows, before reaching a dynamic equilibrium state, display universal behaviour. We show the observed non-equilibrium scaling can be explained using correction of Kolmogorov's energy spectrum. Given universality experimental numerical observations, ideas presented here lay foundation for modeling wide class flows.

Second and third order longitudinal structure functions wavenumber spectra of isotropic turbulence are computed using the EDQNM model compared to results multifractal formalism. At highest Reynolds number available in windtunnel experiments, $R_\lambda=2500$, both give power-law corrections inertial range scaling velocity increment skewness. For EDQNM, this correction is a finite effect, whereas for formalism it an intermittency that persists at any high number. Furthermore, two approaches...

Adding the notion of spatial locality to susceptible-infected-recovered (or SIR) model, allows capture local saturation an epidemic. The resulting minimum model epidemic, consisting five ordinary differential equations with constant coefficients, reproduces slowly decaying periodic outbursts, as observed in COVID-19 or Spanish flu It is shown that if immunity decays, even slowly, yields a fully dynamics.

We analyse the anisotropy of homogeneous turbulence in an electrically conducting fluid submitted to a uniform magnetic field, for low Reynolds number, quasi-static approximation. interpret contradictory earlier predictions between linearized theory and simulations: linear limit, kinetic energy transverse velocity components, normal decays faster than axial component, along field (Moffatt, J. Fluid Mech. , vol. 28, 1967, p. 571); whereas many numerical studies predict final state...

Active matter systems display a fascinating range of dynamical states, including stationary patterns and turbulent phases. While the former can be tackled with methods from field pattern formation, spatio-temporal disorder active turbulence phase calls for statistical description. Borrowing techniques theory, we here establish quantitative description correlation functions spectra minimal continuum model turbulence. Further exploring parameter space, also report on surprising type...

The energy cascade from large to small scales is a robust feature of three-dimensional turbulence. In statistically steady turbulence, the average dissipation in equilibrium with injected system. A global quantity measuring deviations such flux normalised rate Cϵ, corresponding viscous dissipation, by quantities associated largest Recent investigations have pointed out how this varies unsteady flows. We focus on two test-cases assess non-equilibrium isotropic These cases are, respectively,...

The evolution of the turbulent energy spectrum for inviscid spectrally truncated Euler equations is studied by closure calculations. observed behavior similar to one found in direct numerical simulations [Cichowlas, Bonaïtiti, Debbasch, and Brachet, Phys. Rev. Lett. 95, 264502 (2005)]. A Kolmogorov spectral range an equipartition are simultaneously. Between these two ranges a "quasi-dissipative" zone present kinetic spectrum. time wave number that marks beginning analyzed it shown nonlocal...

In this paper, the eddy-damped quasi-normal Markovian closure is used to study behavior of scalar flux spectrum in isotropic turbulence as Reynolds number Reλ varies a range between 30 and 107. The different contributions evolution equation are studied. One-dimensional spectra good agreement with direct numerical simulation (DNS) experiments at moderate Reλ. shows that high numbers, K−7∕3 scaling found for spectrum, Lumley’s prediction [Phys. Fluids 10, 855 (1967)], but enormous needed...

Among existing subgrid scale (SGS) models for large-eddy simulation (LES), some are time reversible in the sense that dynamics evolve backward after a transformation at every point space. In practice, reduce numerical stability of simulations since effect scales is no longer strictly dissipative. This lack constitutes often criterion to reject this kind models. The aim paper examine whether time-reversibility can constitute model has fulfill, or not to. Thereto, we investigate by direct...

Direct numerical simulation data show that the variance of coupling term in passive scalar advection by a random velocity field is smaller than it would be if and fields were statistically independent. This effect analogous to "depression nonlinearity" hydrodynamic turbulence. We trends observed are qualitatively consistent with predictions closure theories related Kraichnan's direct interaction approximation. The phenomenon demonstrated over range Prandtl numbers. In inertial-convective...

Reversed initial fields can generate nonequilibrium decaying turbulence. During the short time interval when reversed flow reorganizes to restore its energy cascade, a new dissipation scaling is observed, ${C}_{\ensuremath{\epsilon}}\ensuremath{\sim}{\mathrm{Re}}_{\ensuremath{\lambda}}^{\ensuremath{-}2}$, for transient with rapidly evolving dissipation.

The comparison of the results direct numerical simulations isotropic turbulence Newtonian and viscoelastic fluid provides evidence that viscoelasticity modifies qualitatively behavior smallest scales: we observe a power law in far dissipation range kinetic energy spectrum show it is robust feature, roughly independent large scale dynamics. A detailed analysis transfer shows at these scales injected into flow through polymer relaxation. It further shown part total transferred among an...

The velocity-scalar cross spectrum (or scalar flux spectrum) is generally presumed to have a K−7/3 wavenumber dependence in the inertial range, agreement with dimensional analysis proposed by Lumley [Phys. Fluids 10, 855 (1967)]. Such behavior is, however, clearly not observed experiments which spectra closer K−2 even less steep) are found. It shown paper that compatible scaling if spectral of correlation introduced. An different terms equation shows two nonlinear contributions can be...

Isotropic, rotating, and stratified turbulent flows are analyzed using a scale- direction-dependent flatness. The anisotropy of the spatial fluctuations energy distribution can hereby be quantified for different length scales. This measure allows one to distinguish between longitudinal transversal intermittency as well horizontal vertical intermittency. difference is argued related incompressiblity constraint. A large turbulence explained by an depletion plane in Fourier space.

A study of the relationship between Lagrangian statistics and flow topology in fluid turbulence is presented. The characterized using Weiss criterion, which provides a conceptually simple tool to partition into topologically different regions: elliptic (vortex dominated), hyperbolic (deformation intermediate (turbulent background). corresponds forced two-dimensional Navier-Stokes doubly periodic circular bounded domains, latter with no-slip boundary conditions. In double domain, probability...

Turbulence governed by the Navier-Stokes equations shows a tendency to evolve towards state in which nonlinearity is diminished. In fully developed turbulence this can be measured comparing variance of nonlinear term same quantity Gaussian field with energy distribution. order study phenomenon at high Reynolds numbers, version Direct Interaction Approximation used obtain closed expression for statistical average mean-square nonlinearity. The wavenumber spectrum evaluated and its scaling...

The response of the small scales isotropic turbulence to periodic large scale forcing is studied using two-point closures. frequency turbulent kinetic energy and dissipation rate, phase shifts among production, energy, are determined as functions Reynolds number. It observed that amplitude exhibit nontrivial number dependence reveals a filtering effect cascade. Perturbation analysis applied understand this behavior which shown depend on distant interactions between widely separated motion....

A model based on two-point closure theory of turbulence is proposed and applied to study the Reynolds number dependency scalar flux spectra in homogeneous shear flow with a cross-stream uniform gradient. For flux, inertial range spectral behavior agrees classical predictions measurements. The streamwise found be good agreement results atmospheric However, both measurements disagree predictions. detailed analysis different terms evolution equation for spectrum shows that nonlinear...

Abstract The decay of scalar variance in isotropic turbulence a bounded domain is investigated. Extending the study Touil, Bertoglio and Shao (2002; Journal Turbulence, 03, 49) to case passive scalar, effect finite size on lengthscales turbulent eddies structures studied by truncating infrared range wavenumber spectra. Analytical arguments based simple model for spectral distributions show that exponent fluctuations proportional ratio Kolmogorov constant Corrsin–Obukhov constant. This result...

In a previous communication (W.J.T. Bos and J.-P. Bertoglio 2006, Phys. Fluids, 18, 031706), self-consistent Markovian triadic closure was presented. The detailed derivation of this is given here, relating it to the Direct Interaction Approximation Quasi-Normal types closure. time-scale needed obtain for both energy spectrum scalar variance determined by evaluating correlation between velocity an advected displacement vector-field. relation latter velocity-scalar stressed, suggesting...