共查询到20条相似文献,搜索用时 15 毫秒
1.
R. Nicodemus S. Grossmann Martin Holthaus 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):385-396
We examine the background flow variational principle for calculating bounds on the energy dissipation rate in turbulent shear
flow, and suggest to select this principle's test functions such that they comply with the small-scale smoothness of real
turbulent velocity fields. A self-consistent algorithm implementing this requirement then yields an upper bound on the dimensionless
dissipation coefficient which shows a weak power-law decrease at high Reynolds numbers, instead of approaching a nonzero constant,
as it did in previous estimates.
Received 26 October 1998 相似文献
2.
Y. Malécot C. Auriault H. Kahalerras Y. Gagne O. Chanal B. Chabaud B. Castaing 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):549-561
The velocity increments statistic in various turbulent flows is analysed through the hypothesis that different scales are
linked by a multiplicative process, of which multiplier is infinitely divisible. This generalisation of the Kolmogorov-Obukhov
theory is compatible with the finite Reynolds number value of real flows, thus ensuring safe extrapolation to the infinite
Reynolds limit. It exhibits a estimator universally depending on the Reynolds number of the flow, with the same law either for Direct Numerical Simulations
or experiments, both for transverse and longitudinal increments. As an application of this result, the inverse dependence
is used to define an unbiased value for a Large Eddy Simulation from the resolved scales velocity statistics. However, the exact shape of the multiplicative
process, though independent of the Reynolds number for a given experimental setup, is found to depend significantly on this
setup and on the nature of the increment, longitudinal or transverse. The asymmetry of longitudinal velocity increments probability
density functions exhibits similarly a dependence with the experimental setup, but also systematically depends on the Reynolds
number.
Received 7 January 2000 and Received in final form 17 March 2000 相似文献
3.
B. Eckhardt S. Grossmann D. Lohse 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(3):541-544
We interpret measurements of the Reynolds number dependence of the torque in Taylor-Couette flow by Lewis and Swinney [Phys.
Rev. E 59, 5457 (1999)] and of the pressure drop in pipe flow by Smits and Zagarola [Phys. Fluids 10, 1045 (1998)] within the scaling theory of Grossmann and Lohse [J. Fluid Mech. 407, 27 (2000)], developed in the context of thermal convection. The main idea is to split the energy dissipation into contributions
from a boundary layer and the turbulent bulk. This ansatz can account for the observed scaling in both cases if it is assumed
that the internal wind velocity introduced through the rotational or pressure forcing is related to the external (imposed) velocity U, by with and for the Taylor-Couette (U inner cylinder velocity) and pipe flow (U mean flow velocity) case, respectively. In contrast to the Rayleigh-Bénard case the scaling exponents cannot (yet) be derived
from the dynamical equations.
Received 9 September 2000 相似文献
4.
《中国科学:物理学 力学 天文学(英文版)》2010,(9)
A theoretical model of turbulent fiber suspension is developed by deriving the equations of Reynolds averaged Navier-Stokes,turbulence kinetic energy and turbulence dissipation rate with the additional term of fibers.In order to close the above equations,the equation of probability distribution function for mean fiber orientation is also derived.The theoretical model is applied to the turbulent channel flow and the corresponding equations are solved numerically.The numerical results are verified by comparisons with the experimental ones.The effects of Reynolds number,fiber concentration and fiber aspect-ratio on the velocity profile,turbulent kinetic energy and turbulent dissipation rate are analyzed.Based on the numerical data,the expression for the velocity profile in the turbulent fiber suspension channel flow,which includes the effect of Reynolds number,fiber concentration and aspect-ratio,is proposed. 相似文献
5.
Shear break-up of reversible fractal clusters is investigated by ultrasound and multiple light scattering in the low shear
regime. We consider a dense suspension of Rayleigh scatterers (particles or clusters) with acoustic properties close to those
of the surrounding liquid so that the attenuation of the ultrasonic coherent field is weak and multiple scattering is negligible.
The concept of variance in local particle volume fraction is used to derive an original expression of the ultrasound scattering
cross-section per unit volume for Rayleigh fractal clusters. On the basis of a scaling law for the shear break-up of aggregates,
then we derive the shear stress dependence of the ultrasound scattered intensity from a suspension of reversible fractal clusters.
In a second part, we present rheo-acoustical experiments to study the shear break-up of hardened red cell aggregates in plane-plane
flow geometry and we examine both the self consistent field approximation and the scaling laws used in microrheological models.
We further compare the ability of acoustical backscattering and optical reflectometry techniques to estimate the critical
disaggregation shear stress and the particle surface adhesive energy. Finally, the microrheological model from Snabre and
Mills [#!ref5!#] based on a fractal approach is shown to describe the non Newtonian behavior of a dense distribution of hardened
red cell aggregates.
Received 12 November 1998 and Received in final form 17 May 1999 相似文献
6.
A. Martin P. Odier J.-F. Pinton S. Fauve 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):337-341
Magnetohydrodynamics studies in laboratory experiments have long been restricted to low magnetic Reynolds number flows, mainly
as a result of the very high magnetic diffusivity λ = 1/μσ of common conducting fluids (μ is the fluid's magnetic permeability
and σ its electrical conductivity). The best conductivities are found in liquid metals which have a unit magnetic permeability,
relative to vacuum. We show experimentally that a suspension of solid particles with a high magnetic permeability in a liquid
metal yields an effective medium that has a high electrical conductivity and an enhanced magnetic permeability. The dispersion
of the beads results from the turbulent fluid motion. The range of accessible magnetic Reynolds number can be increased by
a factor of as much as 4 in our experimental setup.
Received 6 March 2000 and Received in final form 13 July 2000 相似文献
7.
C. Abid C. Barberi Moine F. Papini 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(4):707-714
The aim of this paper is to show the effect of secondary flows caused by natural convection on the laminar-turbulent hydrodynamic
transition. It is not a question of measuring a critical threshold value of Reynolds number of transition but only to estimate
the degree of turbulence in the transition regime, i.e. weak turbulence in the case of superposition (mixed convection) or not (forced convection) of secondary flows on the forced
flow. This is possible thanks to the application of the wavelet transform. The calculation of the H?lder exponent, associated
with the maximum value of the singularity spectrum for two configurations, vertical (forced convection) and horizontal (mixed
convection) allows the degree of turbulence to be measured in both cases. The variation of the H?lder exponent versus the Reynolds number has enabled it to be shown that the secondary flows stabilise the main flow and stifle the beginnings
of the turbulence during the regime of transition to turbulence; these kinds of results have also been shown in literature.
Generally, large-sized secondary flows (for example Dean's flows) stabilise the turbulence. Our work confirms this, through
an experiment carried out in identical conditions for mixed convection (horizontal flow) and forced convection (vertical flow).
Received 30 March 1998 and Received in final form 28 April 1999 相似文献
8.
N. Mordant J.-F. Pinton 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):343-352
We study experimentally the motion of a solid sphere settling under gravity in a fluid at rest. The particle velocity is measured
with a new acoustic method. Variations of the sphere size and density allow measurements at Reynolds numbers, based on limit
velocity, between 40 and 7 000. At all Reynolds numbers, our observations are consistent with the presence of a memory-dependent
force acting on the particle. At short times it has a t
-1/2 behaviour as predicted by the unsteady Stokes equations and as observed in numerical simulations. At long times, the decay
of the memory (Basset) force is better fitted by an exponential behaviour. Comparison of the dynamics of spheres of different
densities for the same Reynolds number show that the density is an important control parameter. Light spheres show transitory
oscillations at Re∼ 400, but reach a constant limit speed.
Received 12 April 2000 and Received in final form 13 July 2000 相似文献
9.
Peter E. Hamlington Dmitry KrasnovThomas Boeck Jörg Schumacher 《Physica D: Nonlinear Phenomena》2012,241(3):169-177
Using high-resolution direct numerical simulations, the height and Reynolds number dependence of high-order statistics of the energy dissipation rate and local enstrophy are examined in incompressible, fully developed turbulent channel flow. The statistics are studied over a range of wall distances, spanning the viscous sublayer to the channel flow centerline, for friction Reynolds numbers Reτ=180 and Reτ=381. The high resolution of the simulations allows dissipation and enstrophy moments up to fourth order to be calculated. These moments show a dependence on wall distance, and Reynolds number effects are observed at the edge of the logarithmic layer. Conditional analyses based on locations of intense rotation are also carried out in order to determine the contribution of vortical structures to the dissipation and enstrophy moments. Our analysis shows that, for the simulation at the larger Reynolds number, small-scale fluctuations of both dissipation and enstrophy show relatively small variations for z+?100. 相似文献
10.
E. Nino C. Serio 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):191-200
The objective of this study has been to experimentally analyze the correlation structure of the strong temporal intermittency
which characterizes pipe flow close to the transition to turbulence. In doing so transitional pipe flow has been analyzed
by Laser Doppler velocimetry and the Reynolds number dependence of the covariance function has been studied. The range which
has been analyzed covers the transition to turbulence and moderately developed turbulence (Reynolds number from 1 500 to 5
000). The correlation structure which has been evidenced is generally in agreement with the deterministic, dynamical, interpretation
of temporal intermittency which explains the intermittent behavior as a result of a saddle node bifurcation. However, the
analysis has evidenced fluctuations even before the onset of turbulence. The structure of these fluctuations is perfectly
autoregressive which leads us to conclude that the transition to turbulence can be viewed as a transition from linear randomness
to (non-linear) homogeneity.
Received 29 March 1999 and Received in final form 6 September 1999 相似文献
11.
S. Bottin H. Chaté 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(1):143-155
We argue on general grounds that the transition to turbulence in plane Couette flow is best studied experimentally at a statistical
level. We present such a statistical analysis of experimental data guided by a parallel investigation of a simple coupled
map lattice model for spatiotemporal intermittency. We confirm that this generic type of spatiotemporal chaos is relevant
in the context of plane Couette flow, where the linear stability of the laminar regime at all Reynolds numbers insures the
necessary local subcriticality. Using large ensembles of similar experiments, we show the existence of a well-defined threshold
Reynolds number above which a unique, turbulent, intermittent attractor coexists with the laminar flow. Furthermore, our data
reveals that this transition to spatiotemporal intermittency is discontinuous, i.e. akin to a first-order phase transition.
Received: 10 April 1998 / Revised: 22 June 1998 / Accepted: 24 June 1998 相似文献
12.
A. Bershadskii T. Nakano D. Fukayama T. Gotoh 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(1):95-101
Using results of a direct numerical simulation (DNS) of 3D turbulence we show that the observed generalized scaling (i.e. scaling moments versus moments of different orders) is consistent with a lognormal-like distribution of turbulent energy dissipation fluctuations
with moderate amplitudes for all space scales available in this DNS (beginning from the molecular viscosity scale up to largest ones). Local multifractal thermodynamics has been developed to interpret the data obtained using the generalized scaling, and a new interval
of space scales with inverse cascade of generalized energy has been found between dissipative and inertial intervals of scales
for sufficiently large values of the Reynolds number.
Received 21 July 2000 相似文献
13.
An energy transfer mechanism in high-temperature supersonic turbulent flow for variable specific heat (VSH) condition through turbulent kinetic energy (TKE), mean kinetic energy (MKE), turbulent internal energy (TIE) and mean internal energy (MIE) is proposed. The similarities of energy budgets between VSH and constant specific heat (CSH) conditions are investigated by introducing a vibrational energy excited degree and considering the effects of fluctuating specific heat. Direct numerical simulation (DNS) of temporally evolving high-temperature supersonic turbulent channel flow is conducted at Mach number 3.0 and Reynolds number 4800 combined with a constant dimensional wall temperature 1192.60 K for VSH and CSH conditions to validate the proposed energy transfer mechanism. The differences between the terms in the two kinetic energy budgets for VSH and CSH conditions are small; however, the magnitude of molecular diffusion term for VSH condition is significantly smaller than that for CSH condition. The non-negligible energy transfer is obtained after neglecting several small terms of diffusion, dissipation and compressibility related. The non-negligible energy transfer involving TIE includes three processes, in which energy can be gained from TKE and MIE and lost to MIE. The same non-negligible energy transfer through TKE, MKE and MIE is observed for both the conditions. 相似文献
14.
《Proceedings of the Combustion Institute》2023,39(2):2419-2427
This work presents results from simultaneous high-resolution temperature and velocity measurements in a series of turbulent non-premixed jet flames. The filtered Rayleigh scattering (FRS)-based temperature measurements demonstrate sufficient signal-to-noise (SNR) and spatial resolution to estimate the smallest scalar length scales and accurately determine dissipation rate fields. A comprehensive set of conditional statistics are used to characterize the small-scale structure, including the dependence of dissipation layer widths on Reynolds number, temperature, and dissipation magnitude. In general, the dissipation layer thickness decrease with increasing Reynolds number and increase with increasing temperature. However, dissipation layer widths show two distinct behaviors with respect to dissipation magnitude. For small dissipation values, increases in magnitude results in broadening of the dissipation layer, while for larger magnitude values of dissipation, the layer widths are thinned, highlighting the complexity of small-scale turbulent mixing. Additionally, measured ratios of the dissipation layer width to the Batchelor length scale are consistent across all Reynolds numbers and agree with previous studies in non-reacting flows. The unique aspect about the current set of measurements is the ability to examine the interaction of dissipation structure with turbulent flow parameters for the first time in turbulent non-premixed flames. Particularly, the strain rate/dissipation relationship is examined and compared to previous studies in non-reacting flows. It is found that the dissipation layers tend to align normal to the principal compressive strain axis and this tendency increases with increasing Reynolds number. For the lowest Reynolds number case, no dependence of the dissipation layer width nor dissipation rate magnitude on strain rate is found. However, for higher Reynolds numbers, a strong dependence of the dissipation layer width and dissipation rate magnitude on the principal compressive strain rate is observed. These results indicate the direct role of the compressive strain rate field on small-scale mixing structure in reacting flows. 相似文献
15.
We report experimental evidence of spatial clustering of dense particles in homogenous, isotropic turbulence at high Reynolds numbers. The dissipation-scale clustering becomes stronger as the Stokes number increases and is found to exhibit similarity with respect to the droplet Stokes number over a range of experimental conditions (particle diameter and turbulent energy dissipation rate). These findings are in qualitative agreement with recent theoretical and computational studies of inertial particle clustering in turbulence. Because of the large Reynolds numbers a broad scaling range of particle clustering due to turbulent mixing is present, and the inertial clustering can clearly be distinguished from that due to mixing of fluid particles. 相似文献
16.
É. Falcon S. Fauve C. Laroche 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):183-186
We report experimental results on the behavior of an ensemble of inelastically colliding particles, excited by a vibrated
piston in a vertical cylinder. When the particle number is increased, we observe a transition from a regime where the particles
have erratic motions (“granular gas”) to a collective behavior where all the particles bounce like a nearly solid body. In
the gas-like regime, we measure the density of particles as a function of the altitude and the pressure as a function of the
number N of particles. The atmosphere is found to be exponential far enough from the piston, and the “granular temperature”, T, dependence on the piston velocity, V, is of the form , where is a decreasing function of N. This may explain previous conflicting numerical results.
Received 1 February 1999 相似文献
17.
18.
B. Dubrulle 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):361-367
We study the scaling properties of heat transfer Nu in turbulent thermal convection at large Prandtl number Pr using a quasi-linear theory. We show that two regimes arise, depending on the Reynolds number Re. At low Reynolds number, NuPr
-1/2 and Re are a function of RaPr
-3/2. At large Reynolds number NuPr
1/3 and RePr are function only of RaPr
2/3 (within logarithmic corrections). In practice, since Nu is always close to Ra
1/3, this corresponds to a much weaker dependence of the heat transfer in the Prandtl number at low Reynolds number than at large
Reynolds number. This difference may solve an existing controversy between measurements in SF6 (large Re) and in alcohol/water (lower Re). We link these regimes with a possible global bifurcation in the turbulent mean flow. We further show how a scaling theory
could be used to describe these two regimes through a single universal function. This function presents a bimodal character
for intermediate range of Reynolds number. We explain this bimodality in term of two dissipation regimes, one in which fluctuation
dominate, and one in which mean flow dominates. Altogether, our results provide a six parameters fit of the curve Nu(Ra, Pr) which may be used to describe all measurements at Pr≥0.7.
Received 27 February 2002 / Received in final form 29 May 2002 Published online 31 July 2002 相似文献
19.
B. Dubrulle F. Hersant 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):379-386
We generalize an analogy between rotating and stratified shear flows. This analogy is summarized in Table 1. We use this analogy
in the unstable case (centrifugally unstable flow vs. convection) to compute the torque in Taylor-Couette configuration, as a function of the Reynolds number. At low Reynolds
numbers, when most of the dissipation comes from the mean flow, we predict that the non-dimensional torque G = T/ν2
L, where L is the cylinder length, scales with Reynolds number R and gap width η, G = 1.46η3/2(1 - η)-7/4
R
3/2. At larger Reynolds number, velocity fluctuations become non-negligible in the dissipation. In these regimes, there is no
exact power law dependence the torque versus Reynolds. Instead, we obtain logarithmic corrections to the classical ultra-hard (exponent 2) regimes: G = 0.50
. These predictions are found to be in excellent agreement with avail-able experimental data. Predictions for scaling of velocity
fluctuations are also provided.
Received 7 June 2001 and Received in final form 7 December 2001 相似文献
20.
J.P. Vishwakarma 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):369-372
The variation of flow-variables with distance, in the flow-field behind a shock wave propagating in a dusty gas with exponentially
varying density, are obtained at different times. The equilibrium flow conditions are assumed to be maintained, and the results
are compared with those obtained for a perfect gas. It is found that the presence of small solid particles in the medium has
significant effects on the variation of density and pressure.
Received 20 October 1999 and Received in final form 9 March 2000 相似文献