Event-Driven Molecular Dynamics Simulation of Hard-Sphere Gas Flows in Microchannels

Classical solution of Navier-Stokes equations with nonslip boundary condition leads to inaccurate predictions of flow characteristics of rarefied gases confined in micro/nanochannels. Therefore, molecular interaction based simulations are often used to properly express velocity and temperature slips at high Knudsen numbers (Kn) seen at dilute gases or narrow channels. In this study, an event-driven molecular dynamics (EDMD) simulation is proposed to estimate properties of hard-sphere gas flows. Considering molecules as hard-spheres, trajectories of the molecules, collision partners, corresponding interaction times, and postcollision velocities are computed deterministically using discrete interaction potentials. On the other hand, boundary interactions are handled stochastically. Added to that, in order to create a pressure gradient along the channel, an implicit treatment for flow boundaries is adapted for EDMD simulations. Shear-Driven (Couette) and Pressure-Driven flows for various channel configurations are simulated to demonstrate the validity of suggested treatment. Results agree well with DSMC method and solution of linearized Boltzmann equation. At low Kn, EDMD produces similar velocity profiles with Navier-Stokes (N-S) equations and slip boundary conditions, but as Kn increases, N-S slip models overestimate slip velocities.

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Test of mean-field equations for two types of hard-sphere systems by a Brownian-dynamics simulation and a molecular-dynamics simulation

Physical Review E ◽

10.1103/physreve.67.062403 ◽

2003 ◽

Vol 67 (6) ◽

Cited By ~ 23

Author(s):

Michio Tokuyama ◽

Hiroyuki Yamazaki ◽

Yayoi Terada

Keyword(s):

Molecular Dynamics ◽

Molecular Dynamics Simulation ◽

Brownian Dynamics ◽

Hard Sphere ◽

Mean Field ◽

Dynamics Simulation ◽

Brownian Dynamics Simulation ◽

Field Equations ◽

Mean Field Equations

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Development of Hybrid Airlift-Jet Pump with Its Performance Analysis

Applied Sciences ◽

10.3390/app8091413 ◽

2018 ◽

Vol 8 (9) ◽

pp. 1413 ◽

Cited By ~ 2

Author(s):

Dan Yao ◽

Kwongi Lee ◽

Minho Ha ◽

Cheolung Cheong ◽

Inhiug Lee

Keyword(s):

Boundary Conditions ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Stokes Equations ◽

Flow Characteristics ◽

Operating Conditions ◽

Navier Stokes ◽

Jet Pump ◽

Two Phase

A new pump, called the hybrid airlift-jet pump, is developed by reinforcing the advantages and minimizing the demerits of airlift and jet pumps. First, a basic design of the hybrid airlift-jet pump is schematically presented. Subsequently, its performance characteristics are numerically investigated by varying the operating conditions of the airlift and jet parts in the hybrid pump. The compressible unsteady Reynolds-averaged Navier-Stokes equations, combined with the homogeneous mixture model for multiphase flow, are used as the governing equations for the two-phase flow in the hybrid pump. The pressure-based methods combined with the Pressure-Implicit with Splitting of Operators (PISO) algorithm are used as the computational fluid dynamics techniques. The validity of the present numerical methods is confirmed by comparing the predicted mass flow rate with the measured ones. In total, 18 simulation cases that are designed to represent the various operating conditions of the hybrid pump are investigated: eight of these cases belong to the operating conditions of only the jet part with different air and water inlet boundary conditions, and the remaining ten cases belong to the operating conditions of both the airlift and jet parts with different air and water inlet boundary conditions. The mass flow rate and the efficiency are compared for each case. For further investigation into the detailed flow characteristics, the pressure and velocity distributions of the mixture in a primary pipe are compared. Furthermore, a periodic fluctuation of the water flow in the mass flow rate is found and analyzed. Our results show that the performance of the jet or airlift pump can be enhanced by combining the operating principles of two pumps into the hybrid airlift-jet pump, newly proposed in the present study.

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FIRST PROJECTION OF THE EQUATION OF MOTION IN THE CYLINDRICAL COORDINATE SYSTEM

Oil and Gas Studies ◽

10.31660/0445-0108-2016-4-90-92 ◽

2016 ◽

pp. 90-92

Author(s):

A. G. Obukhov ◽

R. E. Volkov

Keyword(s):

Coordinate System ◽

Stokes Equations ◽

Equation Of Motion ◽

Cylindrical Coordinate System ◽

Navier Stokes ◽

Gas Flows ◽

Heat Conducting ◽

Complex Flows ◽

Navier Stokes Equations ◽

Cylindrical Coordinate

It is proved that complex flows of the viscous compressible heat-conducting gas, arising during heating the vertical field, have a pronounced axial symmetry. Therefore, for the numerical solution of the full Navier-Stokes equations for description of such gas flows it are advisable to use a cylindrical coordinate system. This paper describes the transformation of the first projection of the equation of motion of the full Navier-Stokes equations system. The result of the transformation is a record of the first projection of the equation of a continuous medium motion in the cylindrical coordinate system.

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Weak-strong uniqueness for the compressible Navier-Stokes equations with a hard-sphere pressure law

Science China Mathematics ◽

10.1007/s11425-017-9272-7 ◽

2018 ◽

Vol 61 (11) ◽

pp. 2003-2016 ◽

Cited By ~ 3

Author(s):

Eduard Feireisl ◽

Yong Lu ◽

Antonín Novotný

Keyword(s):

Hard Sphere ◽

Stokes Equations ◽

Navier Stokes ◽

Strong Uniqueness ◽

Navier Stokes Equations

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Numerical simulation of dispersion and distribution behaviors of hydrogen leakage in the garage with a crossbeam

SIMULATION ◽

10.1177/0037549718825303 ◽

2019 ◽

Vol 95 (12) ◽

pp. 1229-1238 ◽

Cited By ~ 1

Author(s):

Yunhao Li ◽

Juncheng Jiang ◽

Yuan Yu ◽

Qingwu Zhang

Keyword(s):

Mole Fraction ◽

Natural Ventilation ◽

Stokes Equations ◽

Ventilation System ◽

Three Dimensional ◽

Dynamics Simulation ◽

Navier Stokes ◽

Explosion Hazard ◽

Safety Issues ◽

Set Up

A three-dimensional computational fluid dynamics simulation model resolved by the unsteady Reynolds-Averaged Navier–Stokes equations was developed to predict hydrogen dispersion in an indoor environment. The effect of the height of the crossbeam (Hc) on hydrogen dispersion and distribution behaviors in a four-car garage was numerically investigated under fully confined and natural ventilation conditions. For the fully confined condition, the garage was almost completely filled with a flammable hydrogen cloud at t=600 s. In addition, the volumetric ratio of the flammable region, thickness of the hydrogen stratification, and hydrogen mole fraction all increased as Hc increased. When two symmetric ventilation openings were set up, the volumetric ratio of the flammable region decreased by 50% at t=600 s. Moreover, Hc had evident influence on the vertical distribution of hydrogen mole fraction. In addition, there existed little explosion hazard under the height of 1.6 m. The results show that Hc was a non-negligible factor for the safety design of hydrogen in the garage and Hc=0.12 m was the optimal height of the crossbeam. Furthermore, the ventilation system in the present study cannot completely eliminate the risk of hydrogen explosion. The present risk assessment results can be useful to analyze safety issues in automotive applications of hydrogen.

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Numerical simulation of the stalled flow within a vaned centrifugal pump

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/095440620421800407 ◽

2004 ◽

Vol 218 (4) ◽

pp. 425-435 ◽

Cited By ~ 23

Author(s):

K M Guleren ◽

A Pinarbasi

Keyword(s):

Numerical Simulation ◽

Centrifugal Pump ◽

High Speed ◽

Stokes Equations ◽

Reverse Flow ◽

Flow Characteristics ◽

Navier Stokes ◽

Leakage Flow ◽

Navier Stokes Equations ◽

Low Pass

The main goal of the present work is to analyse the numerical simulation of a centrifugal pump by solving Navier-Stokes equations, coupled with the ‘standard k-∊’ turbulence model. The pump consists of an impeller having five curved blades with nine diffuser vanes. The shaft rotates at 890r/min. Flow characteristics are assumed to be stalled in the appropriate region of flowrate levels of 1.31-2.861/s. Numerical analysis techniques are performed on a commercial FLUENT package program assuming steady, incompressible flow conditions with decreasing flowrate. Under stall conditions the flow in the diffuser passage alternates between outward jetting when the low-pass-filtered pressure is high to a reverse flow when the filtered pressure is low. Being below design conditions, there is a consistent high-speed leakage flow in the gap between the impeller and the diffuser from the exit side of the diffuser to the beginning of the volute. Separation of this leakage flow from the diffuser vane causes the onset of stall. As the flowrate decreases both the magnitude of the leakage within the vaneless part of the pump and reverse flow within a stalled diffuser passage increase. As this occurs, the stall-cell size extends from one to two diffuser passages. Comparisons are made with experimental data and show good agreement.

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Effect of a Time-Dependent Stenosis on Flow Through a Tube

Journal of Engineering for Industry ◽

10.1115/1.3604621 ◽

1968 ◽

Vol 90 (2) ◽

pp. 248-254 ◽

Cited By ~ 169

Author(s):

D. F. Young

Keyword(s):

Stokes Equations ◽

Flow Characteristics ◽

Time Dependent ◽

Arterial System ◽

Navier Stokes ◽

Axially Symmetric ◽

Navier Stokes Equations ◽

Flow Through ◽

Dependent Growth ◽

Abnormal Tissue

A common occurrence in the arterial system is the narrowing of arteries due to the development of atherosclerotic plaques or other types of abnormal tissue development. As these growths project into the lumen of the artery, the flow is disturbed and there develops a potential coupling between the growth and the blood flow through the artery. A discussion of the various possible consequences of this interaction is given. It is noted that very small growths leading to mild stenotic obstructions, although not altering the gross flow characteristics significantly, may be important in triggering biological mechanisms such as intimal cell proliferation or changes in vessel caliber. An analysis of the effect of an axially symmetric, time-dependent growth into the lumen of a tube of constant cross section through which a Newtonian fluid is steadily flowing is presented. This analysis is based on a simplified model in which the convective acceleration terms in the Navier-Stokes equations are neglected. Effect of growth on pressure distribution and wall shearing stress is given and possible biological implications are discussed.

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Numerical Study of Wave Slamming on an Oscillating Flap

Volume 8A: Ocean Engineering ◽

10.1115/omae2014-23171 ◽

2014 ◽

Cited By ~ 2

Author(s):

Yanji Wei ◽

Alan Henry ◽

Olivier Kimmoun ◽

Frederic Dias

Keyword(s):

Stokes Equations ◽

Numerical Study ◽

Flow Characteristics ◽

Ocean Waves ◽

Navier Stokes ◽

Time Step ◽

Navier Stokes Equations ◽

Numerical Studies ◽

Wave Slamming ◽

Volume Method

Bottom hinged Oscillating Wave Surge Converters (OWSCs) are efficient devices for extracting power from ocean waves. There is limited knowledge about wave slamming on such devices. This paper deals with numerical studies of wave slamming on an oscillating flap to investigate the mechanism of slamming events. In our model, the Navier–Stokes equations are discretized using the Finite Volume method with the Volume of Fluid (VOF) approach for interface capturing. Waves are generated by a flap-type wave maker in the numerical wave tank, and the dynamic mesh method is applied to model the motion of the oscillating flap. Basic mesh and time step refinement studies are performed. The flow characteristics in a slamming event are analysed based on numerical results. Various simulations with different flap densities, water depths and wave amplitudes are performed for a better understanding of the slamming.

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