Simulations of Micro Gas Flows by the DS-BGK Method

2011 ◽  
Author(s):  
Jun Li
Keyword(s):  
Mean Free Path ◽  
Navier Stokes ◽  
Gas Flows ◽  
Dominant Effect ◽  
Dsmc Method ◽  
Low Velocity ◽  
Navier Stokes Equation ◽  
Reflection Model ◽  
Accommodation Coefficients ◽  
Simulation Results

For gas flows in micro devices, the molecular mean free path is of the same order as the characteristic scale making the Navier-Stokes equation invalid. Recently, some micro gas flows are simulated by the DS-BGK method, which is convergent to the BGK equation and very efficient for low-velocity cases. As the molecular reflection on the boundary is the dominant effect compared to the intermolecular collisions in micro gas flows, the more realistic boundary condition, namely the CLL reflection model, is employed in the DS-BGK simulation and the influence of the accommodation coefficients used in the molecular reflection model on the results are discussed. The simulation results are verified by comparison with those of the DSMC method as criteria.

scholarly journals Comparison and analysis of calculation of Bridge backwater based on Mike21 hydrodynamic model

2021 ◽  
Vol 233 ◽  
pp. 03043
Author(s):  
Jiang Chuan Liu ◽  
Zhu Qiu Hu ◽  
Mao Yuan Zhu
Keyword(s):  
Theoretical Basis ◽  
Impact Analysis ◽  
Navier Stokes ◽  
Efficiency Coefficient ◽  
Navier Stokes Equation ◽  
The Real ◽  
Comparison And Analysis ◽  
Simulation Results ◽  
The Difference ◽  
Local Water

The construction of bridges and other structures across the river will affect the flood discharge capacity and local water potential of the river.Based on navier-Stokes equation of MIKE21FM hydrodynamic module, this paper carries out two-dimensional numerical simulation of part of Shixi River. By optimizing the grid near the piers to reduce the difference brought by the terrain generalized grid of the real river, it simulates and analyzes the length of the curve of yong-high and Yong-water under different flood frequencies,the Nash-Sutcliffe efficiency coefficient and relative error analysis are used to verify the rationality of the results. The simulation results can accurately reflect the real changes of river water level, It provides a theoretical basis for flood impact analysis.

A Study of Bifurcation Design Used in CD-ELISA Micro-Fluidic Platform

2010 ◽  
Author(s):  
Samuel I. En Lin
Keyword(s):  
Coriolis Force ◽  
Clinical Diagnostics ◽  
Biological Molecules ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Safety Testing ◽  
Micro Channels ◽  
Simulation Results ◽  
Incompressible Navier Stokes Equation ◽  
Detection And Quantification

Enzyme-linked immunosorbent assays (ELISA), one of the most common immunoassays, is widely used for detection and quantification of chemical and biological molecules and is becoming more and more important in clinical diagnostics, food safety testing, and environmental monitoring. A major challenge in developing the CD-ELISA is to split the flow (e.g., bio-reagents) evenly on the micro-channels. The Coriolis force resultant from CD rotation can disturb the flow in the splitter region and thus cause the failure mode in delivering the solution from each reservoir in a pre-specified manner. In this study, we investigate on the effects of inlet pressure and Coriolis force on the splitting ratio under two splitter structures. The analysis is based on the incompressible Navier-Stokes equation and the simulation results agree well with our experimental work.

scholarly journals First simulation results of Titan's atmosphere dynamics with a global 3-D non-hydrostatic circulation model

2006 ◽  
Vol 24 (8) ◽  
pp. 2115-2129 ◽  
Author(s):  
I. V. Mingalev ◽  
V. S. Mingalev ◽  
O. V. Mingalev ◽  
B. Kazeminejad ◽  
H. Lammer ◽  
...  
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Wind Speeds ◽  
Neutral Gas ◽  
Complex Simulation ◽  
First Results ◽  
Simulation Results ◽  
Model Region

Abstract. We present the first results of a 3-D General Circulation Model of Titan's atmosphere which differs from traditional models in that the hydrostatic equation is not used and all three components of the neutral gas velocity are obtained from the numerical solution of the Navier-Stokes equation. The current version of our GCM is, however, a simplified version, as it uses a predescribed temperature field in the model region thereby avoiding the complex simulation of radiative transfer based on the energy equation. We present the first simulation results and compare them to the results of existing GCMs and direct wind observations. The wind speeds obtained from our GCM correspond well with data obtained during the Huygens probe descent through Titan's atmosphere. We interpret the most unexpected feature of these data which consist of the presence of a non-monotonicity of the altitude profile of the zonal wind speed between 60 and 75 km.

Periodic motion embedded in plane Couette turbulence: regeneration cycle and burst

2001 ◽  
Vol 449 ◽  
pp. 291-300 ◽  
Author(s):  
GENTA KAWAHARA ◽  
SHIGEO KIDA
Keyword(s):  
Periodic Motion ◽  
Temporal Structure ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Navier Stokes ◽  
Low Velocity ◽  
Mean Velocity ◽  
Navier Stokes Equation ◽  
Time Periodic Solutions ◽  
Regeneration Cycle

Two time-periodic solutions with genuine three-dimensional structure are numerically discovered for the incompressible Navier–Stokes equation of a constrained plane Couette flow. One solution with strong variation in spatial and temporal structure exhibits a full regeneration cycle, which consists of the formation and breakdown of streamwise vortices and low-velocity streaks; the other one, of gentle variation, represents a spanwise standing-wave motion of low-velocity streaks. These two solutions are unstable and the corresponding periodic orbits in the phase space are connected with each other. A turbulent state wanders around the strong one for most of the time except for occasional escapes from it. As a result, the mean velocity profile and the root-mean-squares of velocity fluctuations of the plane Couette turbulence agree very well with the temporal averages of those of this periodic motion. After an occasional escape from the strong solution, the turbulent state reaches the gentle periodic solution and returns. On the way back, it experiences an overshoot accompanied by strong turbulence activity like an intermittent bursting phenomenon.

scholarly journals Effect of viscosity on slip boundary conditions in rarefied gas flows

2019 ◽  
Author(s):  
Nam T. P. Le
Keyword(s):  
Slip Velocity ◽  
Rarefied Gas ◽  
Cross Flow ◽  
Navier Stokes ◽  
Gas Flows ◽  
Gas Temperature ◽  
Slip Boundary ◽  
Rarefied Gas Flows ◽  
Viscosity Models ◽  
Simulation Results

The viscosity of gases plays an important role in the kinetic theory of gases and in the continuum-fluid modeling of the rarefied gas flows. In this paper we investigate the effect of the gas viscosity on the surface properties as surface gas temperature and slip velocity in rarefied gas simulations. Three various viscosity models in the literature such as the Maxwell, Power Law and Sutherland models are evaluated. They are implemented into OpenFOAM to work with the solver “rhoCentralFoam” that solves the Navier-Stokes-Fourier equations. Four test cases such as the pressure driven backward facing step nanochannel, lid-driven micro-cavity, hypersonic gas flows past the sharp 25-55-deg. biconic and the circular cylinder in cross-flow cases are considered for evaluating three viscosity models. The simulation results show that, whichever the first-order or second-order slip and jump conditions are adopted, the simulation results of the surface temperature and slip velocity using the Maxwell viscosity model give good agreement with DSMC data for all cases studied.

scholarly journals Unstable periodic motion in turbulent flows

2006 ◽  
Vol 13 (5) ◽  
pp. 499-507 ◽  
Author(s):  
G. Kawahara ◽  
S. Kida ◽  
L. van Veen
Keyword(s):  
Phase Space ◽  
Periodic Orbit ◽  
Turbulent Flows ◽  
Periodic Motion ◽  
Isotropic Turbulence ◽  
Space Structure ◽  
Navier Stokes ◽  
Low Velocity ◽  
Navier Stokes Equation ◽  
Phase Space Structure

Abstract. Recently found unstable time-periodic solutions to the incompressible Navier-Stokes equation are reviewed to discuss their relevance to plane Couette turbulence and isotropic turbulence. It is shown that the periodic motion embedded in the Couette turbulence exhibits a regeneration cycle of near-wall coherent structures, which consists of formation and breakdown of streamwise vortices and low-velocity streaks. In phase space a turbulent state wanders around the corresponding periodic orbit for most of the time, so that the root-mean-squares of velocity fluctuations of the Couette turbulence agree very well with the temporal averages of those along the periodic orbit. The Kolmogorov universal-range energy spectrum is observed for the periodic motion embedded in high-symmetric turbulence at the Taylor-microscale Reynolds number Reλ=67. A laminarization strategy inspired by investigation of the phase-space structure in the vicinity of the unstable periodic orbit is presented for the Couette turbulence.

Proper Cell Dimension and Number of Particles Per Cell for DSMC

2009 ◽  
Author(s):  
Z. X. Sun ◽  
Y. L. He ◽  
W. Q. Tao
Keyword(s):  
Flow Regime ◽  
Slip Flow ◽  
Mean Free Path ◽  
Cell Dimension ◽  
Transition Flow ◽  
Dsmc Method ◽  
Transition Flow Regime ◽  
Dsmc Simulation ◽  
Simulation Results ◽  
Number Of Particles

Different opinions still exist on some basic principles of DSMC method, such as the proper grid dimension and the proper number of particles in a cell. In this paper DSMC simulation of Poiseuille flow is made to evaluate the dependence of simulation results on cell dimension and number of particles per cell. In the simulation process a self adapting block structured grid system is employed to make sure that the number of particles per cell is constant. The simulation covers both slip flow regime and transition flow regime and each regime covers both high pressure and low pressure. Our simulation results indicate that the number of particles per cell and scaling factor exert little influence on simulation result for both slip flow and transition flow when the number of particles per cell surpasses 5, but the dimension of cell influences the accuracy of result obviously. The error caused by cell dimension decreases as the diminish of cell dimension. It is concluded that in the DSMC method it is necessary to make sure that the cell is less than 1/2 of molecular mean free path.

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