Numerical Investigation of Rough Surfaces: Coupling Approach

2012 ◽  
Author(s):  
Olga Rovenskaya ◽  
Giulio Croce
Keyword(s):  
Domain Size ◽  
Navier Stokes ◽  
Channel Height ◽  
Physical Domain ◽  
Switching Parameter ◽  
Wide Range ◽  
Conservation Of Momentum ◽  
Coupling Approach ◽  
Mach Numbers ◽  
Poiseuille Number

A numerical analysis of the flow field in rough microchannel is carried out decomposing the computational physical domain into kinetic and continuum sub-domains. Each domain size is determined by the value of a proper threshold parameter, based on the local Knudsen number and local gradients of macro-parameters. This switching parameter is computed from a preliminary Navier–Stokes solution throughout the whole physical domain. The solution is then advanced in time simultaneously in both kinetic and continuum domains: the coupling is achieved by matching half fluxes at the interface of the kinetic and Navier–Stokes domains, taking care of the conservation of momentum, energy and mass through the interface. The roughness geometry is modeled as a series of triangular obstructions with a relative roughness up to a maximum of 5% of the channel height. A wide range of Mach numbers is considered, from nearly incompressible to chocked flow conditions and a Reynolds number up to 100. Accuracy and discrepancies between full Navier Stokes, kinetic and coupled solutions are discussed, assessing the range of applicability of first order slip condition in rough geometries. The effect of the roughness is discussed via Poiseuille number as a function of local Knudsen and Mach numbers.

Numerical Investigation of Microflow Over Rough Surfaces: Coupling Approach

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
Olga Rovenskaya ◽  
Giulio Croce
Keyword(s):  
Knudsen Number ◽  
Pressure Ratio ◽  
Domain Size ◽  
Navier Stokes ◽  
Channel Height ◽  
Physical Domain ◽  
Wide Range ◽  
Conservation Of Momentum ◽  
Mach Numbers ◽  
Poiseuille Number

A numerical analysis of the flow field in rough microchannel is carried out decomposing the computational physical domain into kinetic and continuum subdomains. Each domain size is determined by the value of a proper threshold parameter, based on the local Knudsen number and local gradients of macroparameters. This switching parameter is computed from a preliminary Navier–Stokes (NS) solution throughout the whole physical domain. The solution is then advanced in time simultaneously in both kinetic and continuum domains: The coupling is achieved by matching half fluxes at the interface of the kinetic and Navier–Stokes domains, taking care of the conservation of momentum, energy, and mass through the interface. The roughness geometry is modeled as a series of triangular obstructions with a relative roughness up to a maximum of 5% of the channel height. A wide range of Mach numbers is considered, from nearly incompressible to chocked flow conditions 0.001 ≤ Ma ≤ 0.75 and a Reynolds number up to 170. To estimate rarefaction effect, the flow at Knudsen number ranging from 0.01 to 0.08 and fixed pressure ratio has been considered. Accuracy and discrepancies between full Navier–Stokes, kinetic, and coupled solutions are discussed, assessing the range of applicability of first order slip condition in rough geometries. The effect of the roughness is discussed via Poiseuille number as a function of local Knudsen and Mach numbers.

Coupling Kinetic and Continuum Equations for Micro Scale Flow Computations

2011 ◽  
Author(s):  
Giulio Croce ◽  
Olga Rovenskaya
Keyword(s):  
Knudsen Number ◽  
Pressure Ratio ◽  
Navier Stokes ◽  
Physical Domain ◽  
Wide Range ◽  
Direct Numerical Solution ◽  
Conservation Of Momentum ◽  
Flow Through ◽  
Local Parameters ◽  
The Continuum

An hybrid method, coupling the direct numerical solution of the Bhatnagar-Gross-Krook (BGK) kinetic equation and a Navier-Stokes model is presented. The computational physical domain is decomposed into kinetic and continuum sub-domains using an appropriate criteria based on the local Knudsen number and proper gradients of macro-parameters, computed via a preliminary Navier-Stokes solution throughout the whole physical domain. The coupling is achieved by matching half fluxes at the interface of the kinetic and Navier-Stokes domains, thus taking care of the conservation of momentum, energy and mass through the interface. The proposed method is used for the simulation of the flow through a micro-slit. Outlet to inlet pressure ratio of 0.1, 0.5 and 0.9 are considered, for a wide range of Knudsen number. The local parameters (density, velocity and temperature) along symmetry axis show satisfactory agreement with those computed by the continuum model.

scholarly journals Improved theory for shock waves using the OBurnett equations

2021 ◽  
Vol 929 ◽  
Author(s):  
Ravi Sudam Jadhav ◽  
Abhimanyu Gavasane ◽  
Amit Agrawal
Keyword(s):  
Shock Waves ◽  
Stokes Equations ◽  
Direct Simulation Monte Carlo ◽  
Space Velocity ◽  
Navier Stokes ◽  
Wave Flow ◽  
Complex Flow ◽  
Navier Stokes Equations ◽  
Wide Range ◽  
Mach Numbers

The main goal of the present study is to thoroughly test the recently derived OBurnett equations for the normal shock wave flow problem for a wide range of Mach number ( $3 \leq Ma \leq 9$ ). A dilute gas system composed of hard-sphere molecules is considered and the numerical results of the OBurnett equations are validated against in-house results from the direct simulation Monte Carlo method. The primary focus is to study the orbital structures in the phase space (velocity–temperature plane) and the variation of hydrodynamic fields across the shock. From the orbital structures, we observe that the heteroclinic trajectory exists for the OBurnett equations for all the Mach numbers considered, unlike the conventional Burnett equations. The thermodynamic consistency of the equations is also established by showing positive entropy generation across the shock. Further, the equations give smooth shock structures at all Mach numbers and significantly improve upon the results of the Navier–Stokes equations. With no tweaking of the equations in any way, the present work makes two important contributions by putting forward an improved theory of shock waves and establishing the validity of the OBurnett equations for solving complex flow problems.

Enhanced Electroosmotic Flow Through a Nanochannel Patterned With Transverse Periodic Grooves

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
S. Bhattacharyya ◽  
Naren Bag
Keyword(s):  
Shear Stress ◽  
Electroosmotic Flow ◽  
Stress Condition ◽  
Debye Length ◽  
Groove Depth ◽  
Navier Stokes ◽  
Channel Height ◽  
Poisson Equations ◽  
Wide Range ◽  
Flow Through

In this paper, we have analyzed an enhanced electroosmotic flow (EOF) by geometric modulation of the surface of a charged nanochannel. Otherwise, flat walls of the channel are modulated by embedding rectangular grooves placed perpendicular to the direction of the applied electric field in a periodic manner. The modulated channel is filled with a single electrolyte. The EOF within the modulated channel is determined by computing the Navier–Stokes–Nernst–Planck–Poisson equations for a wide range of Debye length. The objective of the present study is to achieve an enhanced EOF in the surface modulated channel. A significant enhancement in average EOF is found for a particular arrangement of grooves with the width of the grooves much higher than its depth and the Debye length is in the order of the channel height. However, the formation of vortex inside the narrow grooves can reduce the EOF when the groove depth is in the order of its width. Results are compared with the cases in which the grooves are replaced by superhydrophobic patches along which a zero shear stress condition is imposed.

scholarly journals Numerical study of the thermosolutal convection in a 3-D cavity submitted to cross gradients of temperature and concentration

2019 ◽  
Vol 23 (3 Part B) ◽  
pp. 1923-1933
Author(s):  
Meriem Ouzaouit ◽  
Btissam Abourida ◽  
Lahoucine Belarche ◽  
Hicham Doghmi ◽  
Mohamed Sannad
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Stokes Equations ◽  
Numerical Study ◽  
Thermosolutal Convection ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Wide Range ◽  
Conservation Of Momentum ◽  
Prandtl Numbers

This study is a contribution to the numerical study of the thermosolutal convection in a 3-D porous cavity filled with a binary fluid submitted to cross gradients of temperature and concentration. The Navier-Stokes equations, mass and energy governing the physical problem are discretized by the finite volume method. The equations of conservation of momentum coupled with the continuity equation are solved using the SIMPLEC algorithm, then the obtained system is solved using the implicit alternating directions method. The numerical simulations, presented here, correspond to a wide range of thermal Rayleigh number (103< Ra < 106) and buoyancy ratio (1 < N < 12). The Lewis and Prandtl numbers were fixed respectively at 5 and 0.71 and the sections dimension ? = D / H = 0.4. The temperature distribution, the flow pattern and the average heat and mass transfer are examined. The obtained results show significant changes in terms of heat and mass transfer, by proper choice of the governing parameters.

Analysis of Mixing and Flow Structure in Different Passive Micromixers

2009 ◽  
Author(s):  
Shakhawat Hossain ◽  
Mubashshir Ahmad Ansari ◽  
Kwang-Yong Kim
Keyword(s):  
Pressure Drop ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Channel Height ◽  
Navier Stokes Equations ◽  
Pressure Drops ◽  
Square Wave ◽  
Mixing Performance ◽  
Wide Range

This work presents a numerical investigation on mixing and flow structures in microchannels with different geometries: zig-zag; square-wave; and curved. To conduct the investigation, geometric parameters, such as the area of the cross-section of channel, height of the channel, axial length of the channel, and number of pitches, are kept constant for all three cases. Analyses of mixing and flow fields have been carried out for a wide range 0.267 to 267 of the Reynolds number. Mixing in the channels has been analyzed by using Navier-Stokes equations with two working fluids, water and ethanol. The results show that the square-wave microchannel yields the best mixing performance, and the curved and the zig-zag microchannels show nearly the same performance for most Reynolds numbers. For all three cases, the pressure drop has been calculated for channels with equal streamwise-lengths. The curved channel exhibits the smallest pressure drop among the microchannels, while the pressure drops in the square-wave and zigzag channels are approximately the same.

scholarly journals Tunable thermo-reversible bicontinuous nanoparticle gel driven by the binary solvent segregation

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yuyin Xi ◽  
Ronald S. Lankone ◽  
Li-Piin Sung ◽  
Yun Liu
Keyword(s):  
Phase Separation ◽  
Domain Size ◽  
Binary Solvent ◽  
Colloidal Systems ◽  
Colloidal Assembly ◽  
Structures And Properties ◽  
Wide Range ◽  
Equilibrium Process ◽  
Equilibrium Structures ◽  
Non Equilibrium

AbstractBicontinuous porous structures through colloidal assembly realized by non-equilibrium process is crucial to various applications, including water treatment, catalysis and energy storage. However, as non-equilibrium structures are process-dependent, it is very challenging to simultaneously achieve reversibility, reproducibility, scalability, and tunability over material structures and properties. Here, a novel solvent segregation driven gel (SeedGel) is proposed and demonstrated to arrest bicontinuous structures with excellent thermal structural reversibility and reproducibility, tunable domain size, adjustable gel transition temperature, and amazing optical properties. It is achieved by trapping nanoparticles into one of the solvent domains upon the phase separation of the binary solvent. Due to the universality of the solvent driven particle phase separation, SeedGel is thus potentially a generic method for a wide range of colloidal systems.

On LES Methods Applied to Seal Geometries

2012 ◽  
Author(s):  
James Tyacke ◽  
Richard Jefferson-Loveday ◽  
Paul Tucker
Keyword(s):  
Maximum Error ◽  
Labyrinth Seal ◽  
Navier Stokes ◽  
Final Solution ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy ◽  
Rans Models ◽  
Flow Through

Nine Large Eddy Simulation (LES) methods are used to simulate flow through two labyrinth seal geometries and are compared with a wide range of Reynolds-Averaged Navier-Stokes (RANS) solutions. These involve one-equation, two-equation and Reynolds Stress RANS models. Also applied are linear and nonlinear pure LES models, hybrid RANS-Numerical-LES (RANS-NLES) and Numerical-LES (NLES). RANS is found to have a maximum error and a scatter of 20%. A similar level of scatter is also found among the same turbulence model implemented in different codes. In a design context, this makes RANS unusable as a final solution. Results show that LES and RANS-NLES is capable of accurately predicting flow behaviour of two seals with a scatter of less than 5%. The complex flow physics gives rise to both laminar and turbulent zones making most LES models inappropriate. Nonetheless, this is found to have minimal tangible results impact. In accord with experimental observations, the ability of LES to find multiple solutions due to solution non-uniqueness is also observed.

Optimization of RANS Solver Simulation Setup for Propeller Open Water Performance Prediction

2015 ◽  
Author(s):  
Mohammed Islam ◽  
Fatima Jahra ◽  
Michael Doucet
Keyword(s):  
Domain Size ◽  
Open Water ◽  
Fractional Factorial ◽  
Navier Stokes ◽  
Calm Water ◽  
Simulation Results ◽  
Open Water Performance ◽  
Thrust And Torque ◽  
Simulation Time ◽  
Fixed Pitch

Mesh and domain optimization strategies for a RANS solver to accurately estimate the open water propulsive characteristics of fixed pitch propellers are proposed based on examining the effect of different mesh and computation domain parameters. The optimized mesh and domain size parameters were selected using Design of Experiments (DoE) methods enabling simulations to be carried out in a limited memory environment, and in a timely manner; without compromising the accuracy of results. A Reynolds-Averaged Navier Stokes solver is used to predict the propulsive performance of a fixed pitch propeller. The predicted thrust and torque for the propeller were compared to the corresponding measurements. A total of six meshing parameters were selected that could affect the computational results of propeller open water performance. A two-level fractional factorial design was used to screen out parameters that do not significantly contribute to explaining the dependent parameters: namely simulation time, propeller thrust and propeller torque. A total of 32 simulations were carried out only to find out that the selected six meshing parameters were significant in defining the response parameters. Optimum values of each of the input parameters were obtained for the DOE technique and additional simulations were run with those parameters. The simulation results were validated using open water experimental results of the same propeller. It was found that with the optimized meshing arrangement, the propeller opens simulation time was reduced by at least a factor of 6 as compared to the generally popular meshing arrangement. Also, the accuracy of propulsive characteristics was improved by up to 50% as compared to published simulation results. The methodologies presented in this paper can be similarly applied to other simulations such as calm water ship resistance, ship propulsion to systematically derive the optimized meshing arrangement for simulations with minimal simulation time and maximum accuracy. This investigation was carried out using STAR-CCM+, a commercial CFD package; however the findings can be applied to any RANS solver.

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