On the orientation of ellipsoidal particles in a turbulent shear flow

Direct numerical simulation (DNS) of small prolate ellipsoidal particles suspended in a turbulent channel flow is reported. The coupling between the fluid and the particles is one-way. The particles are subjected to the hydrodynamic drag force and torque valid for creeping flow conditions. Six different particle cases with varying particle aspect ratios and equivalent response times are investigated. Results show that, in the near-wall region, ellipsoidal particles tend to align with the mean flow direction, and the alignment increases with increasing particle aspect ratio. When the particle inertia increases, the particles are less oriented in the spanwise direction and more oriented in the wall-normal direction. In the core region of the channel, the orientation becomes isotropic.     

Transport and deposition of colliding particles in turbulent channel flows

The purpose of this paper is twofold: (i) to present statistical models that describe particle–turbulence interactions as well as particle–particle collisions and (ii) to gain a better understanding of the effect of inter-particle collisions on transport, deposition, and preferential concentration of heavy particles in turbulent channel flows. The models presented are based on a kinetic equation for the probability density function of the particle velocity distribution in anisotropic turbulent flow. The model predictions compare reasonable well with numerical simulations and properly reproduce the crucial trends of computations.     

Modeling of the turbulent motion of particles in a vertical channel

The results of modeling of the statistical parameters of a turbulent particle motion in a vertical plane channel are presented. The model is based on a kinetic equation for the particle velocity probability density function. The results are compared with direct numerical simulation.     

Diffusion of heavy spherical particles in a turbulent flow

A connection is established between the statistical characteristics of a turbulent flow and the coefficient of diffusion of spherical particles suspended in the flow.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 142–144, November–December, 1979.     

Dynamics of Brownian particles in a turbulent channel flow

Turbulent channel flows with suspended particles are investigated by means of numerical simulations. The fluid velocity is computed by large eddy simulation. Motion of small graphite particles with diameter of 0.01–10 m, corresponding to the Schmidt number, Sc, of 2.87 × 10²–6.22 × 10⁶ and the particle relaxation time in wall unit, _p⁺, of 9.79 × 10^–5–4.51, is computed by Lagrangian particle tracking. Relation between the particle relaxation time and the computed deposition velocity is found to be in good agreement with an empirical relation. The statistics of the particle motion in the vicinity of the wall are studied. Clear differences are found in dynamical behavior of particles with different sizes. Medium size particles show a strong dependence on the structure of the fluid flow, while small and large particles are considerably less sensitive.     

Corrections for spatial velocity derivatives in a turbulent shear flow

Possible corrections for measured spatial velocity derivatives have been inferred from a direct numerical simulation database for a fully developed turbulent channel flow. The magnitude of the correction depends much less on the distance from the wall for derivatives in the spanwise direction than for those in the wall-normal direction. Corrections based on local isotropy are better approximations for spanwise derivatives than for wall-normal derivatives.The support of the Australian Research Council is gratefully ackowledged.     

Gravitational sedimentation of aggregating particles in a shear flow

A theoretical model describing the sedimentation of aggregating particles under the influence of gravity in Couette shear flow is proposed. The relation between the parameters characterizing the dependence of the sedimentation properties on the shear rate and the parameters characterizing the aggregation of the particles is traced.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 95–98, March–April, 1989.The authors wish to thank S. A. Regirer for useful discussions.     

Modeling plane turbulent Couette flow

Among the salient features of shear-driven plane Couette flow is the constancy of the total shear stress (viscous and turbulent) across the flow. This constancy gives rise to a quasi-homogenous core region, which makes the bulk of the flow substantially different from pressure-driven Poiseuille flow. The present second-moment closure study addresses the conflicting hypotheses relating to turbulent Couette flow. The inclusion of a new wall-proximity function in the wall-reflection part of the pressure-strain model seems mandatory, and the greement with recent experimental and direct numerical simulation (DNS) results is encouraging. Analysis of model computations in the range 750 ≤ Re ≤ 35,000 and comparisons with low-Re DNS data suggest that plane Couette flow exhibits a local-equilibrium core region, in which anisotropic, homogeneous turbulence prevails. However, the associated variation of the mean velocity in the core, as obtained by the model, conflicts with the intuitively appealing assumption of homogeneous mean shear. The constancy of the velocity gradient exhibited by the DNS therefore signals a deficiency in the modeled transport equation for the energy dissipation rate.     

Deposition of inertial particles from a turbulent pipe flow

An explicit formula is derived for the rate of deposition of large particles (droplets) on a tube wall in two-phase turbulent flow. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 68–75, March–April, 1998. The work was financially supported by the International scientific foundation INTAS (grant No. 94-4348) and by the Russian Foundation for Fundamental Research (project No. 97-01-00398).     

A low shear rate turbulent flow apparatus

This paper describes some experiments on a turbulent flow viscometer consisting of a continuous pipe loop of transparent material mounted on a circular wheel. The wheel is partially filled with fluid and rotated at a constant speed. The results show that the apparatus gives sensible results and although only a limited range of Reynolds numbers is possible it can be used as a useful qualitative apparatus to test dilute fluids which have abnormal turbulent flow properties.     

Modeling of vertical turbulent exchange in a stratified near-wall flow

A modified model of turbulence is proposed to describe the processes of vertical transport in inhomogeneous turbulent flows. This model includes algebraic relations for the Reynolds stresses and turbulent-exchange coefficients. Using this model, the growth of the depth of a mixed layer under the action of the wind load in neutral and stable stratified near-wall flows has been predicted. The calculation results for a stable stratified flow that were obtained using the modified and standard two-parametric models of turbulence are compared with experimental data. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 6, pp. 57–64, November–December, 1998.     

Influence of particles on turbulent flow in channels

In this work, the equations of balance of the second single-point moments of pulsations of the carrier phase are used to analyze the influence of particles on the intensity of pulsation motion. Besides dissipation due to pulsation phase slip, these equations take account the effect of dissipation of small-scale vortices on the particles and also of the additional transfer of pulsations by particles due to the particles being drawn into the pulsating motion and the migration of particles across the flow.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 40–48, January–February, 1985.     

Influence of suspended particles on the structure of a turbulent flow in a tube

The results of an experimental investigation into the dispersed flow of a system subject to negative pressure gradients are presented. The measurements were based on an optical time-of-flight method in a water channel, using polystyrene spheres as the solid phase. The average and pulsational characteristics of the dispersed flow were obtained in the boundary (wall) region and also in the center (core) of the flow. For zero pressure gradient the influence of the solid phase expressed itself as a reduction in the level of turbulence and an increase in the extent of the viscous sublayer, leading to a fall in the coefficient of friction. For a negative pressure gradient the pressure of the solid phase generated small-scale vortices, reduced the extent of the viscous sublayer, and hence increased the coefficient of surface friction.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 111–118, March–April, 1976.The author wishes to thank Yu. A. Buevich for interest in this work and V. L. Zalukaev for participation in the experiments.     

An interpretation of the stability of a turbulent shear flow near a rough wall

A conventional, small perturbation, stability analysis has been applied to a fully developed turbulent shear flow in a parallel duct with rough walls. This is an attempt to detect the inherent state of flow stability to quasi-regular disturbances emanating from the surface roughness elements. The surface roughness is represented by the usual roughness Reynolds number; it is fed into the analysis through an assumed mean velocity profile valid between the viscous sublayer and the inner (wall) region. An eddy viscosity model is used to secure the equation closure and the final equation for the perturbation amplitude has been solved numerically using the techniques developed for the Orr-Sommerfeld equation.Within the domain of realistic flow conditions, and for a range of surface roughness amplitudes, a local minimum of stability in terms of the longitudinal wave number has been found. However, it is not implied that it is a minimum minomorum, as only a limited range of surface roughnesses has been tried.     

Relaxational properties of a turbulent shear flow across a cylinder in the presence of a plate

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 61–67, November–December, 1990.     

A computer algorithm for the identification of temperature fronts in a turbulent shear flow

A computer algorithm is developed for the detection of temperature fronts. VITA, or variable interval time averaging, first detects instants at which fronts occur at a reference location of a spanwise array of temperature sensors. The number of detections is subsequently reduced by examining correlations between the temperature signal at the reference location and signals at all other locations over short durations in the vicinity of the original instants. A further reduction in the number of detections is obtained using an iterative procedure in which ensemble averages of temperature are computed at the reference location and correlated with temperature signals at other locations. The performance of the algorithm is discussed in the context of ensemble averages obtained in the self-preserving region of a turbulent plane jet.     

A multipoint method for detecting coherent features in a turbulent shear flow

A technique is presented for the computer detection of temperature fronts in a turbulent shear flow. The detection variable is the product, averaged over a given duration, of temperature fluctuations at a given number of spatial locations. Efficient algorithms are developed for computing the product and for determining accurately the instants of detection, aided by simulations, using model temperature fronts. Ensemble averages of temperature and velocity are obtained for the self-preserving region of a turbulent plane jet.