Introduction to Isotropic Turbulence

Rms turbulent velocities, u ' , created by four peripheral variable speed fans, were measured by Particle Image Velocimetry, PIV, which indicated near-uniform, isotropic turbulence, with small mean velocities.

Here, we describe an experimental study on the dynamics of thin cylindrical shells resembling broken bottle fragments settling through quiescent fluid and homogeneous anisotropic turbulence.

This study presents the effects of the conservation error of turbulent kinetic energy on the isotropic turbulence field.

These features can be successfully predicted by modern models that take into account the specifics of flows with heterogeneous anisotropic turbulence.

The simulation was conducted within a constant volume with an isotropic turbulence condition under 40 bar.

In this work, we analyze the capacity of the superstatistics construction to provide modeling of the velocity field probability density functions (PDFs) of isotropic turbulence.

We present a quantitative analysis of the inertial range statistics produced by entropic lattice Boltzmann method (ELBM) in the context of three-dimensional homogeneous and isotropic turbulence.

These flow mechanisms comprise a shear layer near the interface, lateral momentum transfer and strong secondary currents due to the non-isotropic turbulence.

We study turbulent properties of the ISM to show that, in the case where the break scale traces a transition to isotropic turbulence, the fraction of required accretion energy to sustain turbulent motions in the ISM increases significantly.

This noise prediction model relies on the accuracy of the turbulence spectrum, which is usually assumed to be the von Kármán energy spectrum for isotropic turbulence.

Anisotropic turbulence of the Reynolds Stress Model (RSM) is used in modeling turbulent fluid (natural gas) and.

This indicates that the lower PMSE layers are associated with more anisotropic turbulence scattering.

The proposed power spectrum can handle general non-Kolmogorov, anisotropic turbulence but reduces to Kolmogorov, isotropic case if the power law exponents of temperature and salinity are set to 11/3 and anisotropy coefficient is set to unity.

Based on the data analyses, anisotropic turbulence was observed in the cascade.

In addition, the capability and potential of the newly implemented WENO7M scheme in KARFS to perform DNS of compressible flows is also demonstrated with model problems involving shocks, isotropic turbulence, detonations and flame propagation into a stratified mixture with complex chemical kinetics.

Numerical simulations of forced anisotropic turbulence (FAT) in a periodic box and homogeneous shear turbulence (HST) at various turbulent Mach (Ma${}_{\mathrm{T}}$) and Taylor Reynolds numbers are performed to study the anisotropy of kinetic energy (KE) transfer in compressible homogeneous turbulence.

It is shown that vertical velocity in clouds indeed can be represented as a sum of convective velocity (forming zone of cloud updrafts and subsiding shell) and a stochastic velocity obeying laws of homogeneous and isotropic turbulence.

The overall approach represents a combination of wall-blocking (non-local) and wall-viscous (low-Reynolds number) effects encountered in anisotropic turbulence.

For isotropic turbulence, in which l ∥ = l ∧ , Sonsrettee et al.

In these works, it is also shown that the developed two-fluid model is able to adequately describe complex anisotropic turbulences.

This experiment is used to study the origin of statistical irreversibility and the prevalence of direct over inverse energy cascades in isotropic turbulence.

Also, we find that the turbine generates its own kind of turbulence that dominates the ambient turbulence and has strong features of homogeneous, isotropic turbulence.

Using the mesh-free finite mass method as an example, we show that the anisotropic model is best able to reproduce the proper Kolmogorov inertial range scaling in homogeneous, isotropic turbulence.

These results were found in both isotropic and anisotropic turbulence fields.

Temporal evolution of the scaling exponent from Fourier power analysis suggests slightly below the classical Kolmogorov value of −5/3 for the three-dimensional homogeneous and isotropic turbulence.

Although bereft of spatial variation, they accurately reproduce the main statistical properties of fully-developed homogeneous and isotropic turbulence.

One direction of research is to investigate anisotropic turbulence intensities, id est to investigate the distribution of Reynolds stresses and energy spectra in a square cross-section channel, downstream of a semi-active jet turbulence grid generating anisotropic turbulent airflow.

Further, to understand the deviation from the isotropic turbulence, the turbulence triangle, Eigen values, and the invariant functions are presented at the downstream of the grid for the three oscillating flow cases.

We propose a new theory of pair diffusion in homogeneous, isotropic turbulence hypothesizing that not only structures of size l, but much larger ones also induce significant pair separation—ignored in the R-O theory.

Droplet evaporation and combustion in isotropic turbulence were considered.

We test the utility of these particles by measuring their dissolution rates in homogeneous, isotropic turbulence in our laboratory turbulence tank.

We present a method to identify such manifolds, and we apply it to a reduced model for the Lagrangian evolution of field gradients in homogeneous and isotropic turbulence with a passive scalar.

Standard models are often not sufficient to accurately predict vortices, which can have a huge impact on the performance, since based on the assumption of isotropic turbulence.

, laminar burning velocity, turbulent burning velocity) of diethyl ether (DEE)/air mixtures under different pre-ignition quasi-isotropic turbulence velocity.

The results show the estimation of the deviation measure from the isotropic turbulence in view of Reynolds stress tensor for turbulent flow in the presence of seepage through the channel bed.

An enhanced disparity of the turbulent normal stresses is observed inside the inertial subrange for the heated case, indicating a stronger deviation from isotropic turbulence, which possibly challenges mostly isotropic standard turbulence models.

This work is aimed at establishing a theoretical method for predicting confined methane-air explosion pressure under isotropic turbulence.

We complement these results by performing numerical integration of the Maxey–Riley equation for a point bubble experiencing nonlinear drag in three-dimensional, homogeneous and isotropic turbulence.

Comparison is made with homogeneous-isotropic turbulence, in which case the average vorticity in the strain eigenframe is layer-like, has wings of opposite vorticity, and the strain configuration is found to be super-Townsend.

The present work also demonstrates that the use of anisotropic turbulence models, which may become more common in the future due to the evolution of engine architectures, must be done carefully because of the sensitivity of the models to the anisotropic parameters which are difficult to assess from RANS simulations.

The turbulent wave activity (slope in the power spectrum) reduces with a decrease in gas shear, and shows similarities to the decay of homogeneous and isotropic turbulence.

It is found that in isotropic turbulence fractional derivative order $\alpha \sim 0.

These ingredients are inhomogeneity due to boundaries, anisotropic turbulence, and rotation.

Linear two equation models are often not able to represent these effects correctly since their derivation is based on over-simplifications, such as the Boussinesq hypothesis, which makes it impossible to capture anisotropic turbulence.

A three-dimensional remeshed smoothed particle hydrodynamics method for the simulation of isotropic turbulence is used, the method is coupled with Brinkman penalisation technique for flow simulation inside the complex valve geometry.

A framework is proposed to investigate the behavior of LES flame surface density models for simple academic cases, here the development of a statistically one-dimensional flame in an homogenous and isotropic turbulence, by comparison with a prescribed reference solution.

This study presents the effects of spatial resolution anisotropy on an isotropic turbulence field.

These polynomials, denoted by Sn(x) and called special polynomials, were first discovered in a study of a certain family of isotropic turbulence fields.

An experimental investigation of the time-dependent spatial distribution of droplet concentration in a “box” of stationary homogeneous and isotropic turbulence without mean flow was performed for polydispersed droplet clouds with a wide range of mean droplet diameters and droplet size distributions, characterized by a representative Stokes number, based on the droplet arithmetic diameter and the Kolmogorov time scale of the flow, varying between 0.

62 at 298 K, using the same dual-chamber, fan-stirred cruciform burner capable of generating near-isotropic turbulence.

The simulations show that simple laminar initial conditions produce similar levels of mixing as advanced initial conditions with tilted swirl and anisotropic turbulence.

We illustrate this method for a simple, isotropic turbulence model and we find remarkable agreement with the results of numerical studies.

The primary vortex core is accompanied by spirally wrapped secondary vortex tubes, resulting in anisotropic turbulence structure around the vortex core regions.

A close analogy between the energy transfer from large to small scales in isotropic turbulence and the momentum transfer in the wall normal direction in WBT plays a key role in the application.

In this work, a direct anisotropic filter (DAF) method is proposed to produce desired velocity spectra of three-dimensional anisotropic turbulence, based on a direct form of anisotropic filter that can be implemented directly to obtain non-Gaussian spectra.

In the decade or so below the Ozmidov wavenumber (N3/e)1/2, that is, on scales between those attributed to internal gravity waves and isotropic turbulence, ocean and atmosphere measurements.

Straightforward application of standard analyses developed in isotropic turbulence sometimes masks important aspects of the anisotropic turbulence.

Recent experiments have confirmed the existence of both isotropic and anisotropic turbulence near the ground.

In this work, the two-point probability density function (PDF) for the velocity field of isotropic turbulence is modeled using the kappa distribution and the concept of superstatistics.

This alignment stands in stark contrast to observations from previous studies in turbulent Bunsen flames or flames in isotropic turbulence, indicating the significance of bulk strain rate in determining local strain-flame alignment.

By using a large databases of isotropic turbulence, generated from numerical simulations of the Navier-Stokes equations over a wide range of Reynolds numbers, we show that circulation exhibits a bifractal behavior at the highest Reynolds number considered: space filling for moments up to order $3$ and a mono-fractal with an unchanging dimension of about $2.

Lagrangian analysis of homogeneous, isotropic turbulence shows that attainment of this bound is associated with relatively short durations and an upper limit to the spatial extent of the flow structures that is similar to the Taylor scale.

First, we investigate the physical imaging mechanism in kinds of turbulence conditions, including the isotropic turbulence and the anisotropic turbulence.

However, the overall differences are reduced when multiple wavenumber components are superposed in isotropic turbulence, and the sound pressure levels are therefore close as in subsonic flows.

Modernization was held on the base of isotropic turbulence noise measuring techniques.

As an initial step in evaluating the WOF-X method, synthetic particle images from a 2D DNS of isotropic turbulence are processed and the results are compared to a typical correlation-based PIV algorithm and previous optical flow methods.