The global transport of heat and momentum in turbulent convection is constrained by thin thermal viscous boundary layers at the heated cooled boundaries system. This bottleneck thought to be lifted once themselves become fully very high values Rayleigh number [Formula: see text]-the dimensionless parameter that describes vigor convective turbulence. Laboratory experiments cylindrical cells for text] have reported different outcomes on putative law. Here we show, direct numerical simulations...

From a database of direct numerical simulations homogeneous and isotropic turbulence, generated in periodic boxes various sizes, we extract the spherically symmetric part moments velocity increments first verify following (somewhat contested) results: $4/5$-ths law holds an intermediate range scales that second order exponent over same is {\it{anomalous}}, departing from self-similar value $2/3$ approaching constant $0.72$ at high Reynolds numbers. We compare with some typical theories...

This paper revisits the communication complexity of large-scale 3D fast Fourier transforms (FFTs) and asks what impact trends in current architectures will have on FFT performance at exascale. We analyze both memory hierarchy traffic network to derive suitable analytical models, which we calibrate against software implementations; then evaluate models make predictions about potential scaling outcomes exascale, based extrapolating technology trends. Of particular interest is choosing...

Using the largest database of isotropic turbulence available to date, generated by direct numerical simulation (DNS) Navier-Stokes equations on an 8192^{3} periodic box, we show that longitudinal and transverse velocity increments scale identically in inertial range. By examining DNS data at several Reynolds numbers, infer contradictory results past inertial-range universality are artifacts low number residual anisotropy. We further both locally averaged dissipation rate, just as postulated...

Significance Circulation around closed loops is important in classical and quantum fluids, as well condensed matter the solid state. This paper deals with statistical theory of circulation high–Reynolds number turbulence has implications for structure turbulent vorticity, which a quantity central interest turbulence. We focus particularly on so-called area rule. The rule states that properties contours depend solely minimal surface contour, not its shape. demonstrate works to good...

The turbulence problem at the level of scaling exponents is hard in part because multifractal small scales, which demands that each moment order be treated and understood independently. This conclusion derives from studies velocity structure functions, energy dissipation, enstrophy density (that is, square vorticity), etc. However, it likely there exist other physically pertinent quantities with uncomplicated inertial range, potentially resulting huge simplifications theory. We show...

The intermittency of a passive scalar advected by three-dimensional Navier-Stokes turbulence at Taylor-scale Reynolds number $650$ is studied using direct numerical simulations on $4096^3$ grid; the Schmidt unity. By measuring increment moments high orders, while ensuring statistical convergence, we provide unambiguous evidence that scaling exponents saturate to $1.2$ for moment order beyond about $12$, indicating dominated most singular shock-like cliffs in field. We show fractal dimension...

The influence of vortical structures on the transport and mixing passive scalars is investigated. Initial conditions are taken from a direct numerical simulation database forced homogeneous isotropic turbulence, with scalar fluctuations, driven by uniform mean gradient, performed for Taylor microscale Reynolds numbers (R λ) 140 240, Schmidt 1/8 1. For each R λ, after reaching fully developed turbulent regime, which statistically steady, Coherent Vorticity Extraction applied to flow. It shown...

A class of spectral subgrid models based on a self-similar and reversible closure is studied with the aim to minimize impact scales inertial range fully developed turbulence. In this manner, we improve scale extension where anomalous exponents are measured by roughly one order magnitude, when compared direct numerical simulations or other popular closures at same resolution. We found first indication that intermittency for high moments not captured many phenomenological so far.

In high-resolution direct numerical simulations, it is found that, independent of the anisotropic content energy containing eddies, small-scale turbulent fluctuations recover isotropy and universality faster than previously reported.

Direct numerical simulations show that a tracer introduced into turbulent homogeneous medium will not be fully mixed. Natural barriers are present, across which the concentration jumps, typically from smallest to largest value. An analysis of these mixing characteristics is presented.

An extensive direct numerical simulation database over a wide range of Reynolds and Schmidt numbers is used to examine the number dependence structure function passive scalars applicability so-called Yaglom's relation in isotropic turbulence with uniform mean scalar gradient. For moderate available, limited scales fields very low (as as 1/2048) seen lead weaker intermittency, alignment between velocity gradients principal strain rates. Strong departures from both Obukhov-Corrsin scaling for...

The refined similarity hypotheses of Kolmogorov, regarded as an important ingredient intermittent turbulence, has been tested in the past using one-dimensional data and plausible surrogates energy dissipation. We employ from direct numerical simulations, at microscale Reynolds number ${R}_{\ensuremath{\lambda}}\ensuremath{\sim}650$, on a periodic box ${4096}^{3}$ grid points to test three-dimensional averages. In particular, we study small-scale properties stochastic variable...

Inertial-range features of turbulence are investigated using data from experimental measurements grid and direct numerical simulations isotropic simulated in a periodic box, both at the Taylor-scale Reynolds number ${R}_{\ensuremath{\lambda}}\ensuremath{\sim}1000$. In particular, oscillations modulating power-law scaling inertial range examined for structure functions up to sixth-order moments. The exponent ratios decrease with increasing sample size simulations, although experiments they...

Using direct numerical simulations of isotropic turbulence in periodic cubes several sizes, the largest being $8192^3$ yielding a microscale Reynolds number $1300$, we study properties pressure Laplacian to understand differences inertial range scaling enstrophy density and energy dissipation. Even though is difference between two highly intermittent quantities, it non-intermittent essentially follows Kolmogorov scaling, at least for low-order moments. this property, show that exponents...

Statistical moments of the turbulent circulation are complex geometry-dependent functionals closed oriented contours and present a hard challenge for theoretical understanding. Conveniently defined moment ratios, however, empirically known to have appreciable geometric dependency only at lower orders that sized near bottom inertial range, in situation where they span minimal surfaces equivalent areas. Resorting ideas addressed framework vortex gas model statistics, which integrates...

The dissipation of kinetic energy in a turbulent flow is controlled by the competition between random pushing and pulling fluid parcels. If motions average each other out with increasing turbulence intensity, then must decay will be conserved inviscid limit. This work highlights this pivotal dependence rate on small-scale turbulence.

We use well-resolved direct numerical simulations of high-Reynolds-number turbulence to study a fundamental statistical property -- the asymmetry velocity increments with likely implications on important dynamics. This property, ignored by existing small-scale phenomenological models, manifests most prominently in non-monotonic trend increment moments (or structure functions) moment order, and differences between ordinary absolute functions for given separation distance. show that high-order...