Fully Resolved Simulations of Stationary Particles in Turbulent Flow

2003 ◽  
Author(s):  
Tristan M. Burton ◽  
John K. Eaton
Keyword(s):  
Gas Flow ◽  
Isotropic Turbulence ◽  
Numerical Models ◽  
Particle Surface ◽  
Particle Diameter ◽  
Grid Method ◽  
Slip Boundary Condition ◽  
Slip Boundary ◽  
Kolmogorov Length Scale ◽  
Turbulence Modification

Gas flows containing a dilute loading of solid particle constitute an important class of multiphase flows. In most cases the gas flow is turbulent, and the interactions between the particles and the turbulence offer major modeling challenges. Many numerical models implicitly assume that the particles are significantly smaller than all turbulence length scales. Simple particle drag laws derived for uniform steady flow around a sphere are used to compute the motion of point-particles, and to determine the magnitude of the point-forces that are applied to the gas phase in order to produce turbulence modification. This technique may be appropriate if the particle is small relative to any turbulent eddies, but in many practical problems the particle diameter, d, is of the same order as the flow Kolmogorov scale, η. Here we perform fully-resolved simulations of a fixed particle in decaying homogeneous isotropic turbulence using an overset grid method. All flow scales are accurately resolved with this technique including the effect of the no-slip boundary condition at the particle surface. A set of 29 simulations with an initial Taylor microscale Reynolds number, Reλ = 32.2, and Kolmogorov length scale, η = 0.45d are computed to obtain a useful statistical sample. The turbulent kinetic energy and viscous dissipation near the particle surface in laden and unladen simulations are compared to provide understanding of the turbulence modification process. We anticipate that these results will provide direction for the development of turbulence modification models suitable for larger scale simulations where the flow cannot be resolved to the particle surface.

Rarefaction and Compressibility Effects in Gas Microflows

1996 ◽  
Vol 118 (3) ◽  
pp. 448-456 ◽  
Author(s):  
Ali Beskok ◽  
George Em Karniadakis ◽  
William Trimmer
Keyword(s):  
Incompressible Flows ◽  
Numerical Models ◽  
Slip Flow ◽  
Slip Boundary Condition ◽  
Partial Slip ◽  
Micro Electro Mechanical Systems ◽  
Slip Boundary ◽  
Gas Microflows ◽  
Computational Modeling And Simulation ◽  
Compressibility Effects

Gas microflows are encountered in many applications of Micro-Electro-Mechanical Systems (MEMS). Computational modeling and simulation can provide an effective predictive capability for heat and momentum transfer in microscales as well as means of evaluating the performance of a new microdevice before hardware fabrication. In this article, we present models and a computational methodology for simulating gas microflows in the slip-flow regime for which the Knudsen number is less than 0.3. The formulation is based on the classical Maxwell/Smoluchowski boundary conditions that allow partial slip at the wall. We first modify a high-order slip boundary condition we developed in previous work so that it can be easily implemented to provide enhanced numerical stability. We also extend a previous formulation for incompressible flows to include compressibility effects which are primarily responsible for the nonlinear pressure distribution in micro-channel flows. The focus of the paper is on the competing effects of compressibility and rarefaction in internal flows in long channels. Several simulation results are presented and comparisons are provided with available experimental data. A specific set of benchmark experiments is proposed to systematically study compressibility, rarefaction and viscous heating in microscales in order to provide validation to the numerical models and the slip-flow theory in general as well as to establish absolute standards in this relatively young field of fluid mechanics.

Numerical Analysis of Rarefaction and Compressibility Effects in Bent Microchannels

2010 ◽  
Author(s):  
O. Rovenskaya ◽  
G. Croce
Keyword(s):  
Gas Flow ◽  
Flow Characteristics ◽  
Wall Slip ◽  
Outer Wall ◽  
Slip Boundary Condition ◽  
Central Line ◽  
Navier Stokes ◽  
Strong Impact ◽  
First Order ◽  
Slip Boundary

Numerical investigation of a gas flow through microchannels with a sharp, 90 degrees bend is carried out using Navier-Stokes (N-S) equations with the classical Maxwell first-order slip boundary condition, including the tangential gradient effect due to the wall curvature, and Smoluchowski first order temperature jump definition. The details of the flow structure near the corner are analyzed, investigating the competing effects of rarefaction and compressibility on the channel performances. The flow characteristics in terms of velocity profiles, slip velocity distribution along inner and outer wall, pressure, average Mach number along central line of the channel have been presented. The results showed that impact of the bend on the channel performances is smaller at high rarefaction levels. The behaviour of pressure and velocity away from the bend is similar to that of a straight microchannel; however, the asymmetry in the flow at the bend, with high velocities and high velocity gradients on its inner side, has a strong impact on wall slip velocities. The presence of a recirculation is detected on both the inner and outer walls of the corner for larger Reynolds. However, rarefaction may delay the onset of recirculation. It is also observed that the mass flux through a bend microchannel can even be slightly larger than that through a straight microchannel of the same length and subjected to the same pressure difference.

A Friction Factor Correlation for Gas Flow in Parallel Plate Microchannels by Considering Combined Effects of Compressibility and Rarefaction

2008 ◽  
Author(s):  
Xiaohong Yan ◽  
Qiuwang Wang
Keyword(s):  
Friction Factor ◽  
Velocity Gradient ◽  
Parallel Plate ◽  
Gas Flow ◽  
Stokes Equations ◽  
Control Volume ◽  
Slip Flow ◽  
Slip Boundary Condition ◽  
Combined Effects ◽  
Slip Boundary

The effects of compressibility and rarefaction for gas flow in microchannels have been extensively studied separately. However, these two effects are always combined for gas flow in microchannels. In this paper, the two-dimensional compressible Navier-Stokes equations are solved for gas flow in parallel plate channels with a slip boundary condition to study the combined effects of compressibility and rarefaction on the friction factor. The numerical methodology is based on the control volume finite difference scheme. It is found that the effect of compressibility increases the velocity gradient near the wall which then increases the friction factor. On the other hand, increasing the velocity gradient near the wall leads to a much larger slip velocity and implies a stronger rarefaction effect and a corresponding decrease in the friction factor. These two opposite effects make the effect of compressibility on friction factor for slip flow weaker than that for no-slip compressible flow. A correlation among fRe, Kn and Ma is presented. The correlation is validated with available experimental and analytical results.

Liquid Leak Predictions in Micro- and Nanoporous Gaskets

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Lotfi Grine ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Gas Flow ◽  
Stokes Equations ◽  
Slip Flow ◽  
Slip Boundary Condition ◽  
Navier Stokes ◽  
Experimental Conditions ◽  
Navier Stokes Equations ◽  
Slip Boundary ◽  
Gas Leak ◽  
Flow Through

In recent years, quite few experimental and theoretical studies have been conducted to predict gas leak rate through gaskets. However, a very limited work is done on liquid leak rates through gaskets. The slip flow model is used to predict liquid flow through porous gaskets based on measurements of gas flow at different pressures. In fact, an extrapolation of the porosity parameter approach (Grine, L., and Bouzid, A., 2009, “Correlation of Gaseous Mass Leak Rates Through Micro and Nano-Porous Gaskets,” ASME Paper No. PVP2009-77205) used to correlate leak rates between different gases is used to predict liquid leak rates. In the present article, an analytical-computational methodology based on the number and pore size to predict liquid micro- and nanoflows in the slip flow regime through gaskets is presented. The formulation is based on the Navier–Stokes equations associated with slip boundary condition at the wall. The mass leak rates through a gasket considered as a porous media under various experimental conditions of fluid media, pressure, and gasket stress were conducted on a special gasket test rig. Gaseous and liquid leaks are measured and comparisons with the analytical predictions are made.

scholarly journals Isotropic-turbulence-induced mass transfer across a severely contaminated water surface

2016 ◽  
Vol 797 ◽  
pp. 665-682 ◽  
Author(s):  
H. Herlina ◽  
J. G. Wissink
Keyword(s):  
Mass Transfer ◽  
Schmidt Number ◽  
Isotropic Turbulence ◽  
Slip Boundary Condition ◽  
Gas Transfer ◽  
Transfer Velocity ◽  
Slip Conditions ◽  
Slip Boundary ◽  
Turbulent Reynolds Number ◽  
Solid Liquid

Direct numerical simulations were performed to investigate the effect of severe contamination on interfacial gas transfer in the presence of isotropic turbulence diffusing from below. A no-slip boundary condition was employed at the interface to model the severe contamination effect. The influence of both Schmidt number ($Sc$) and turbulent Reynolds number ($R_{T}$) on the transfer velocity ($K_{L}$) was studied. In the range from $Sc=2$ up to $Sc=500$ it was found that $K_{L}\propto Sc^{-2/3}$, which is in agreement with predictions based on solid–liquid transport models, see e.g. Davies (1972, Turbulence Phenomena, Academic). For similar $R_{T}$, the transfer velocity was observed to reduce significantly compared with the free-slip conditions. The reduction becomes more pronounced with increasing Schmidt number. Similar to the observation for free-slip conditions made by Theofanous et al. (Intl J. Heat Mass Transfer, vol. 19 (6), 1976, pp. 613–624), the normalized $K_{L}$ in the present no-slip case was also found to depend on $R_{T}^{-1/2}$ and $R_{T}^{-1/4}$ for small and large turbulent Reynolds numbers, respectively.

Experimental and Numerical Studies on Gas Flow Through Silicon Microchannels

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
K. Srinivasan ◽  
P. M. V. Subbarao ◽  
S. R. Kale
Keyword(s):  
Boundary Condition ◽  
Gas Flow ◽  
Stokes Equations ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Slip Boundary Condition ◽  
Second Order ◽  
Navier Stokes ◽  
Slip Boundary ◽  
Aspect Ratios

The present work investigates the extension of Navier–Stokes equations from slip-to-transition regimes with higher-order slip boundary condition. To achieve this, a slip model based on the second-order slip boundary condition was derived and a special procedure was developed to simulate slip models using FLUENT®. The boundary profile for both top and bottom walls was solved for each pressure ratio by the customized user-defined function and then passed to the FLUENT® solver. The flow characteristics in microchannels of various aspect ratios (a = H/W = 0.002, 0.01, and 0.1) by generating accurate and high-resolution experimental data along with the computational validation was studied. For that, microchannel system was fabricated in silicon wafers with controlled surface structure and each system has several identical microchannels of same dimensions in parallel and the processed wafer was bonded with a plane wafer. The increased flow rate reduced uncertainty substantially. The experiments were performed up to maximum outlet Knudsen number of 1.01 with nitrogen and the second-order slip coefficients were found to be C1 = 1.119–1.288 (TMAC = 0.944–0.874) and C2 = 0.34.

scholarly journals Numerical Study of Nanoparticle Deposition in a Gaseous Microchannel under the Influence of Various Forces

Micromachines ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 47
Author(s):  
Fubing Bao ◽  
Hanbo Hao ◽  
Zhaoqin Yin ◽  
Chengxu Tu
Keyword(s):  
Drag Force ◽  
Particle Deposition ◽  
Gas Flow ◽  
Numerical Study ◽  
Velocity Slip ◽  
Slip Boundary Condition ◽  
Deposition Efficiency ◽  
Nanoparticle Deposition ◽  
Thermophoretic Force ◽  
Slip Boundary

Nanoparticle deposition in microchannel devices inducing contaminant clogging is a serious barrier to the application of micro-electro-mechanical systems (MEMS). For micro-scale gas flow fields with a high Knudsen number (Kn) in the microchannel, gas rarefaction and velocity slip cannot be ignored. Furthermore, the mechanism of nanoparticle transport and deposition in the microchannel is extremely complex. In this study, the compressible gas model and a second-order slip boundary condition have been applied to the Burnett equations to solve the flow field issue in a microchannel. Drag, Brownian, and thermophoretic forces are concerned in the motion equations of particles. A series of numerical simulations for various particle sizes, flow rates, and temperature gradients have been performed. Some important features such as reasons, efficiencies, and locations of particle deposition have been explored. The results indicate that the particle deposition efficiency varies more or less under the actions of forces such as Brownian force, thermophoretic force, and drag force. Nevertheless, different forces lead to different particle motions and deposition processes. Brownian or thermophoretic force causes particles to move closer to the wall or further away from it. The drag force influence of slip boundary conditions and gas rarefaction changes the particles’ residential time in the channel. In order to find a way to decrease particle deposition on the microchannel surface, the deposition locations of different sizes of particles have been analyzed in detail under the action of thermophoretic force.

New slip boundary condition in high-speed rarefied gas flow simulations

2019 ◽  
Vol 234 (3) ◽  
pp. 840-856
Author(s):  
Nam TP Le ◽  
Nam H Tran ◽  
Thoai N Tran ◽  
Toan T Tran
Keyword(s):  
Boundary Condition ◽  
High Speed ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Slip Boundary Condition ◽  
Mean Free Path ◽  
Slip Condition ◽  
Monte Carlo Data ◽  
Flow Simulations ◽  
Slip Boundary

In this paper, we propose a new slip boundary condition in hypersonic gas flow simulations. It is derived by considering the Langmuir isotherm adsorption into the Kaniadarkis et al. model of the kinetic theory of gas. Moreover, the motion of the adsorbed molecules over the surface (i.e. surface diffusion) is considered for the calculation of the mean free path in new slip condition. Three aerodynamic configurations are selected for evaluating new slip condition such as (1) the sharp-leading-edge flat plate, (2) circular cylinder in cross-flow, and (3) the sharp 25°–55° biconic cases. Hypersonic gas flows have the Mach number ranging from 6.1 to 15.6, and the working gases are argon and nitrogen. The simulation results show that new slip condition predicts better slip velocity than the Maxwell slip condition and gives good agreement with the direct simulation Monte-Carlo data for all cases considered in the present work.

Subsonic gas flow in a straight and uniform microchannel

2002 ◽  
Vol 472 ◽  
pp. 125-151 ◽  
Author(s):  
YITSHAK ZOHAR ◽  
SYLVANUS YUK KWAN LEE ◽  
WING YIN LEE ◽  
LINAN JIANG ◽  
PIN TONG
Keyword(s):  
Gas Flow ◽  
Theoretical Calculations ◽  
Slip Flow ◽  
Velocity Slip ◽  
Slip Boundary Condition ◽  
Perturbation Expansions ◽  
Slip Boundary ◽  
Flow Parameters ◽  
Pressure Distributions ◽  
Flow Effects

A nonlinear equation based on the hydrodynamic equations is solved analytically using perturbation expansions to calculate the flow field of a steady isothermal, compressible and laminar gas flow in either a circular or a planar microchannel. The solution takes into account slip-flow effects explicitly by utilizing the classical velocity-slip boundary condition, assuming the gas properties are known. Consistent expansions provide not only the cross-stream but also the streamwise evolution of the various flow parameters of interest, such as pressure, density and Mach number. The slip-flow effect enters the solution explicitly as a zero-order correction comparable to, though smaller than, the compressible effect. The theoretical calculations are verified in an experimental study of pressure-driven gas flow in a long microchannel of sub-micron height. Standard micromachining techniques were utilized to fabricate the microchannel, with integral pressure microsensors based on the piezoresistivity principle of operation. The integrated microsystem allows accurate measurements of mass flow rates and pressure distributions along the microchannel. Nitrogen, helium and argon were used as the working fluids forced through the microchannel. The experimental results support the theoretical calculations in finding that acceleration and non-parabolic velocity profile effects were found to be negligible. A detailed error analysis is also carried out in an attempt to expose the challenges in conducting accurate measurements in microsystems.

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