scholarly journals On the transition between turbulence regimes in particle-laden channel flows

2018 ◽  
Vol 845 ◽  
pp. 499-519 ◽  
Author(s):  
Jesse Capecelatro ◽  
Olivier Desjardins ◽  
Rodney O. Fox
Keyword(s):  
Reynolds Number ◽  
Fluid Phase ◽  
Stokes Number ◽  
Channel Flows ◽  
High Mass ◽  
Inertial Particles ◽  
Mass Loading ◽  
Two Phase ◽  
Phase Dynamics ◽  
Wide Range

Turbulent wall-bounded flows exhibit a wide range of regimes with significant interaction between scales. The fluid dynamics associated with single-phase channel flows is predominantly characterized by the Reynolds number. Meanwhile, vastly different behaviour exists in particle-laden channel flows, even at a fixed Reynolds number. Vertical turbulent channel flows seeded with a low concentration of inertial particles are known to exhibit segregation in the particle distribution without significant modification to the underlying turbulent kinetic energy (TKE). At moderate (but still low) concentrations, enhancement or attenuation of fluid-phase TKE results from increased dissipation and wakes past individual particles. Recent studies have shown that denser suspensions significantly alter the two-phase dynamics, where the majority of TKE is generated by interphase coupling (i.e.  drag) between the carrier gas and clusters of particles that fall near the channel wall. In the present study, a series of simulations of vertical particle-laden channel flows with increasing mass loading is conducted to analyse the transition from the dilute limit where classical mean-shear production is primarily responsible for generating fluid-phase TKE to high-mass-loading suspensions dominated by drag production. Eulerian–Lagrangian simulations are performed for a wide range of particle loadings at two values of the Stokes number, and the corresponding two-phase energy balances are reported to identify the mechanisms responsible for the observed transition.

Study on Entrainment From High-Viscosity Falling Liquid Film of Counter-Current Two-Phase Flow in a Vertical Pipe

2004 ◽  
Author(s):  
Yasuo Koizumi ◽  
Ryou Enari ◽  
Hiroyasu Ohtake
Keyword(s):  
Reynolds Number ◽  
Liquid Film ◽  
Silicon Film ◽  
Water System ◽  
Water Film ◽  
Two Phase ◽  
Silicon Oil ◽  
Falling Liquid Film ◽  
Wide Range ◽  
Counter Current

Behavior of a falling liquid film of highly viscous fluid in the counter-current flow condition was examined. In experiments, water and silicon oils of 500, 1000 and 3000 cSt were used as the liquid phase and air was adopted as the gas phase. A test section vertically oriented was a circular pipe of 30 mm in inner diameter and 5.4 m in length. Flooding velocities of the air-water system were well correlated with traditional correlations such as the Wallis correlation and the Kamei correlation. However, the flooding velocities of silicon films were greatly lower than the expected. When the effect of the viscosity was incorporated into the Wallis correlation, it predicted the experimental results well. The flooding in the air-silicon system was initiated by sudden growth of a wave on the film as in the air-water system although the film Reynolds number of the falling silicon film was considerably low; 0.02 ∼ 4. A considerable amount of droplets were detected a long time before the initiation of flooding in the air–silicon oil experiments as well as in the air–water experiments. The correlations tested for the onset condition of entrainment gave much higher gas velocities than the measured. Predicted velocities were rather close to the flooding velocities. The falling film thickness was predicted well by applying the universal velocity profile to the film flow over a wide range of a film Reynolds number; ranging from a water film to a 3000 cSt silicon oil film.

Numerical Computation for Flow-Induced Oscillations of a Circular Cylinder

2010 ◽  
Author(s):  
Norio Kondo
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
High Reynolds Number ◽  
Numerical Results ◽  
High Mass ◽  
Mass Ratio ◽  
Reynolds Number Flow ◽  
Wide Range ◽  
Number Flow ◽  
High Reynolds

This paper presents numerical results for flow-induced oscillations of an elastically supported circular cylinder, which is immersed in a high Reynolds number flow. The flow-induced oscillations of the circular cylinder at subcritical Reynolds numbers have been investigated by many researchers, and the interested phenomena with respect to the oscillations have been found in a wide range of the Scruton number. For the flow-induced oscillation of the circular cylinder with high mass ratio, it is well-known that there is the peak value of amplitudes at near the critical reduced velocity. Therefore, we computer flow-induced oscillations of a circular cylinder with a mass ratio of 8, which is placed in a high Reynolds number flow, by three-dimensional simulation, and the numerical results are compared with the results of flow-induced oscillations of the circular cylinder immersed in a subcritical Reynolds number flow.

Two-Phase Convective Cooling for Ultrahigh Power Dissipation in Microprocessors

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Peter A. Kottke ◽  
Thomas M. Yun ◽  
Craig E. Green ◽  
Yogendra K. Joshi ◽  
Andrei G. Fedorov
Keyword(s):  
High Heat ◽  
Heat Fluxes ◽  
High Mass ◽  
Two Phase ◽  
Worst Case ◽  
Pressure Drops ◽  
System Pressure ◽  
Performance Trends ◽  
Wide Range ◽  
Contraction And Expansion

We present results of modeling for the design of microgaps for the removal of high heat fluxes via a strategy of high mass flux, high quality, and two-phase forced convection. Modeling includes (1) thermodynamic analysis to obtain performance trends across a wide range of candidate coolants, (2) evaluation of worst-case pressure drop due to contraction and expansion in inlet/outlet manifolds, and (3) 1D reduced-order simulations to obtain realistic estimates of different contributions to the pressure drops. The main result is the identification of a general trend of improved heat transfer performance at higher system pressure.

scholarly journals Investigation of the Horizontal Motion of Particle-Laden Jets

Computation ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 23 ◽  
Author(s):  
Tooran Tavangar ◽  
Hesam Tofighian ◽  
Ali Tarokh
Keyword(s):  
Reynolds Number ◽  
Gravitational Force ◽  
Dispersion Model ◽  
Passive Scalar ◽  
Stokes Number ◽  
Industrial Applications ◽  
Horizontal Motion ◽  
Jet Flows ◽  
Mass Loading ◽  
Particle Laden Jets

Particle-laden jet flows can be observed in many industrial applications. In this investigation, the horizontal motion of particle laden jets is simulated using the Eulerian–Lagrangian framework. The two-way coupling is applied to the model to simulate the interaction between discrete and continuum phase. In order to track the continuum phase, a passive scalar equation is added to the solver. Eddy Life Time (ELT) is employed as a dispersion model. The influences of different non-dimensional parameters, such as Stokes number, Jet Reynolds number and mass loading ratio on the flow characteristics, are studied. The results of the simulations are verified with the available experimental data. It is revealed that more gravitational force is exerted on the jet as a result of the increase in mass loading, which deflects it more. Moreover, with an increase in the Reynolds number, the speed of the jet rises, and consequently, the gravitational force becomes less capable of deviating the jet. In addition, it is observed that by increasing the Stokes number, the particles leave the jet at higher speed, which causes a lower deviation of the jet.

Reynolds number scaling of inertial particle statistics in turbulent channel flows

2014 ◽  
Vol 758 ◽  
Author(s):  
Matteo Bernardini
Keyword(s):  
Reynolds Number ◽  
Turbulent Flows ◽  
Large Scale ◽  
Spatial Organization ◽  
Reynolds Numbers ◽  
Stokes Number ◽  
Wall Region ◽  
Inertial Particles ◽  
Turbulent Channel Flows ◽  
Strong Segregation

AbstractThe effect of the Reynolds number on the behaviour of inertial particles in wall-bounded turbulent flows is investigated through large-scale direct numerical simulations (DNS) of particle-laden canonical channel flow spanning almost a decade in the friction Reynolds number, from $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\mathit{Re}_{\tau } = 150$ to $\mathit{Re}_{\tau } = 1000$. Lagrangian particle tracking is used to study the motion of six different particle sets, described by a Stokes number in the range $\mathit{St} = 1\text {--}1000$. At all Reynolds numbers a strong segregation in the near-wall region is observed for particles characterized by intermediate Stokes number, in the range $\mathit{St} =10\text {--}100$. The wall-normal concentration profiles of such particles collapse in inner scaling, thus suggesting the independence of the turbophoretic drift from the large-scale outer motions. This observation is also supported by the spatial organization of the suspended phase in the inner layer, which is found to be universal with the Reynolds number. The deposition rate coefficient increases with $\mathit{Re}_{\tau }$ for a given $\mathit{St}$. Suitable inner and outer scalings are proposed to collapse the deposition curves across the available ranges of Reynolds and Stokes numbers for the different deposition regimes.

Numerical prediction on deposition of micro-particulate matter in turbulent channel flows

2015 ◽  
Vol 26 (12) ◽  
pp. 1550134 ◽  
Author(s):  
Bing Wang ◽  
Jing Lin
Keyword(s):  
Particulate Matter ◽  
Particle Deposition ◽  
Prediction Models ◽  
Stokes Number ◽  
Particle Dispersion ◽  
Channel Flows ◽  
Inertial Particles ◽  
Navier Stokes Equation ◽  
Deposition Rates ◽  
Turbulent Channel Flows

A direct numerical simulation of Navier–Stokes equation coupled to the Lagrangian tracking of individual particles was used to predict the dispersion of deposited micro-particulate matter in turbulent channel flows on the walls. The different interaction conditions between particles and walls were considered for particles with Stokes numbers ranging from 0.1 to 104. The particle deposition rates were predicted accurately because of the accurate calculation of turbulence and particle dispersion. It was found the interaction between the turbulent particles and the walls determined the re-entrainment mechanism of inertial particles away from the wall. The dispersion of deposition of particles were independent of the wall conditions in the partial diffusional and whole diffusion-impaction regime, consistent with a log–log law with particle Stokes number, which was found to be [Formula: see text]. The deposition rate decreased with decreasing adhesion of the wall in the inertia-moderated regime. The present results may be helpful for establishing and evaluating accurate prediction models of micro-particle deposition rates in various engineering applications.

scholarly journals Two-phase modelling for sediment water mixtures above the limit deposit velocity in horizontal pipelines

2021 ◽  
Vol 69 (3) ◽  
pp. 263-274
Author(s):  
Thijs Schouten ◽  
Cees van Rhee ◽  
Geert Keetels
Keyword(s):  
Pressure Gradient ◽  
Land Reclamation ◽  
Particle Diameter ◽  
Mesh Size ◽  
Fluid Phase ◽  
Two Phase ◽  
Algebraic Form ◽  
Continuity Equations ◽  
Wide Range ◽  
Euler Solver

Abstract In dredging applications, deep sea mining and land reclamation projects typically large amounts of sediments are transported through pipes in the form of hyper concentrated (40% sediment or more) sediment-water mixtures or slurries. In this paper it is investigated how well a generic Euler-Euler CFD-model is capable to model velocity, concentration profiles and the pressure gradient of sediment above deposition limit velocity in a pipeline. This Euler-Euler solver treats both phases as a continuum with its own momentum and continuity equations. The full kinetic theory for granular flows is accounted for (no algebraic form is used) and is combined with a buoyant k-ε turbulence model for the fluid phase. The influence of the mesh size has been checked and grid convergence is achieved. All numerical schemes used are of second-order accuracy in space. The pressure gradient was calibrated by adjusting the specularity coefficient in one calibration case and kept constant afterwards. Simulations were carried out in a wide range of slurry flow parameters, in situ volume concentration (9–42%), pipe diameter (0.05–0.90 m), particle diameter (90–440 μm) and flow velocity of (3–7 m/s). The model shows satisfactory agreement to experimental data from existing literature.

scholarly journals New Perspective for Heat Transfer Evaluation During Film Condensation Inside Tubes

2021 ◽  
Vol 39 (2) ◽  
pp. 390-402
Author(s):  
Yanán Camaraza-Medina
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Single Phase ◽  
Film Condensation ◽  
Mean Deviation ◽  
Two Phase ◽  
Wide Range ◽  
The Mean ◽  
Vertical Tubes

This paper presents the main results of the research developed by the author in his postdoctoral investigations on heat transfer calculations during film condensation inside tubes. The elements studied are combined in an analysis expression that provides a reasonable fit with the available experimental data, which includes a total of 22 fluids, including water, refrigerants and a wide range of organic substances, which condense inside horizontal, inclined and vertical tubes. These experimental data were obtained from the reports of 33 sources. Available data covers tube diameters from 2 to 50 mm, mass flow rates from 3 to 850 kg/(m2s), reduced pressures ranging from 0.0008 to 0.91, values for single-phase from 1 to , Reynolds number for two-phase from 900 to 594390, Reynolds number for single-phase from 65 to 84950 and vapor quality from 0.01 to 0.99. The mean deviation found for the analyzed data for horizontal tubes was 13.4%, while for the inclined and vertical tubes data the mean deviation was 14.9%. In all cases, the agreement of the proposed model is good enough to be considered satisfactory for practical design.

scholarly journals Experimental study of inertial particles clustering and settling in homogeneous turbulence

2019 ◽  
Vol 864 ◽  
pp. 925-970 ◽  
Author(s):  
Alec J. Petersen ◽  
Lucia Baker ◽  
Filippo Coletti
Keyword(s):  
Reynolds Number ◽  
Fluid Velocity ◽  
Stokes Number ◽  
Terminal Velocity ◽  
Solid Particles ◽  
Homogeneous Turbulence ◽  
Small Scale ◽  
Inertial Particles ◽  
Mean Flow ◽  
Integral Scale

We study experimentally the spatial distribution, settling and interaction of sub-Kolmogorov inertial particles with homogeneous turbulence. Utilizing a zero-mean-flow air turbulence chamber, we drop size-selected solid particles and study their dynamics with particle imaging and tracking velocimetry at multiple resolutions. The carrier flow is simultaneously measured by particle image velocimetry of suspended tracers, allowing the characterization of the interplay between both the dispersed and continuous phases. The turbulence Reynolds number based on the Taylor microscale ranges from $Re_{\unicode[STIX]{x1D706}}\approx 200{-}500$, while the particle Stokes number based on the Kolmogorov scale varies between $St_{\unicode[STIX]{x1D702}}=O(1)$ and $O(10)$. Clustering is confirmed to be most intense for $St_{\unicode[STIX]{x1D702}}\approx 1$, but it extends over larger scales for heavier particles. Individual clusters form a hierarchy of self-similar, fractal-like objects, preferentially aligned with gravity and with sizes that can reach the integral scale of the turbulence. Remarkably, the settling velocity of $St_{\unicode[STIX]{x1D702}}\approx 1$ particles can be several times larger than the still-air terminal velocity, and the clusters can fall even faster. This is caused by downward fluid fluctuations preferentially sweeping the particles, and we propose that this mechanism is influenced by both large and small scales of the turbulence. The particle–fluid slip velocities show large variance, and both the instantaneous particle Reynolds number and drag coefficient can greatly differ from their nominal values. Finally, for sufficient loadings, the particles generally augment the small-scale fluid velocity fluctuations, which however may account for a limited fraction of the turbulent kinetic energy.

scholarly journals Influence of Microscale Turbulent Droplet Clustering on Radar Cloud Observations

2014 ◽  
Vol 71 (10) ◽  
pp. 3569-3582 ◽  
Author(s):  
Keigo Matsuda ◽  
Ryo Onishi ◽  
Masaaki Hirahara ◽  
Ryoichi Kurose ◽  
Keiko Takahashi ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Stokes Number ◽  
Number Density ◽  
Model Estimate ◽  
Density Spectrum ◽  
Radar Observations ◽  
Wavenumber Range ◽  
Proposed Model ◽  
Wide Range ◽  
Clustering Data

Abstract This study investigates the influence of microscale turbulent clustering of cloud droplets on the radar reflectivity factor and proposes a new parameterization to account for it. A three-dimensional direct numerical simulation of particle-laden isotropic turbulence is performed to obtain turbulent clustering data. The clustering data are then used to calculate the power spectra of droplet number density fluctuations, which show a dependence on the Taylor microscale-based Reynolds number (Reλ) and the Stokes number (St). First, the Reynolds number dependency of the turbulent clustering influence is investigated for 127 < Reλ < 531. The spectra for this wide range of Reλ values reveal that Reλ = 204 is sufficiently large to be representative of the whole wavenumber range relevant for radar observations of atmospheric clouds. The authors then investigate the Stokes number dependency for Reλ = 204 and propose an empirical model for the turbulent clustering influence assuming power laws for the number density spectrum. For Stokes numbers less than 2, the proposed model can estimate the influence of turbulence on the spectrum with an RMS error less than 1 dB when calculated over the wavenumber range relevant for radar observations. For larger Stokes number droplets, the model estimate has larger errors, but the influence of turbulence is likely negligible in typical clouds. Applications of the proposed model to two idealized cloud observing scenarios reveal that microscale turbulent clustering can cause a significant error in estimating cloud droplet amounts from radar observations with microwave frequencies less than 13.8 GHz.

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