scholarly journals Employing Per-Component Time Step in DSMC Simulations of Disparate Mass and Cross-Section Gas Mixtures

2013 ◽  
Vol 14 (3) ◽  
pp. 703-721
Author(s):  
Roman V. Maltsev
Keyword(s):  
Direct Simulation Monte Carlo ◽  
Silver Deposition ◽  
Time Step ◽  
New Approach ◽  
Silver Nanocluster ◽  
Stationary Flows ◽  
Molecular Masses ◽  
Simulation Monte Carlo ◽  
Disparate Mass ◽  
Computational Resources

AbstractA new approach to simulation of stationary flows by Direct Simulation Monte Carlo method is proposed. The idea is to specify an individual time step for each component of a gas mixture. The approach consists of modifications mainly to collision phase simulation and recommendations on choosing time step ratios. It allows lowering the demands on the computational resources for cases of disparate collision diameters of molecules and/or disparate molecular masses. These are cases important e.g., in vacuum deposition technologies. Few tests of the new approach are made. Finally, the usage of new approach is demonstrated on a problem of silver nanocluster diffusion in argon carrier gas under conditions of silver deposition experiments.

scholarly journals Modified Sonine approximation for granular binary mixtures

2009 ◽  
Vol 623 ◽  
pp. 387-411 ◽  
Author(s):  
VICENTE GARZÓ ◽  
FRANCISCO VEGA REYES ◽  
JOSÉ MARÍA MONTANERO
Keyword(s):  
Transport Coefficients ◽  
Direct Simulation Monte Carlo ◽  
Boltzmann Distribution ◽  
Three Dimensions ◽  
Navier Stokes ◽  
State Distribution ◽  
New Approach ◽  
Viscosity Coefficients ◽  
Stokes Transport ◽  
Simulation Monte Carlo

We evaluate in this work the hydrodynamic transport coefficients of a granular binary mixture in d dimensions. In order to eliminate the observed disagreement (for strong dissipation) between computer simulations and previously calculated theoretical transport coefficients for a monocomponent gas, we obtain explicit expressions of the seven Navier–Stokes transport coefficients by the use of a new Sonine approach in the Chapman–Enskog (CE) theory. This new approach consists of replacing, where appropriate in the CE procedure, the Maxwell–Boltzmann distribution weight function (used in the standard first Sonine approximation) by the homogeneous cooling state distribution for each species. The rationale for doing this lies in the well-known fact that the non-Maxwellian contributions to the distribution function of the granular mixture are more important in the range of strong dissipation we are interested in. The form of the transport coefficients is quite common in both standard and modified Sonine approximations, the distinction appearing in the explicit form of the different collision frequencies associated with the transport coefficients. Additionally, we numerically solve by the direct simulation Monte Carlo method the inelastic Boltzmann equation to get the diffusion and the shear viscosity coefficients for two and three dimensions. As in the case of a monocomponent gas, the modified Sonine approximation improves the estimates of the standard one, showing again the reliability of this method at strong values of dissipation.

Influence of rarefaction on the computation of aerodynamic parameters in hypersonic flow

2002 ◽  
Vol 216 (6) ◽  
pp. 277-290 ◽  
Author(s):  
G Zuppardi ◽  
D Paterna
Keyword(s):  
Experimental Data ◽  
Direct Simulation Monte Carlo ◽  
Navier Stokes ◽  
Time Step ◽  
Transitional Regime ◽  
Physical Conditions ◽  
Aerodynamic Parameters ◽  
Simulation Monte Carlo ◽  
Probable Path ◽  
Interplanetary Mission

The results from two well-known and widely accepted codes, the Navier—Stokes solver FLUENT and the direct simulation Monte Carlo (DSMC) solver DS2G, have been analysed in order to fix the levels of the flow field rarefaction where the codes can work properly for the computation of aerodynamic forces and heat flux on a spacecraft during the re-entry. This subject has already been widely investigated; thus the purpose of the present work is to provide a further contribution. In order to make realistic computations, a probable path of a typical capsule, returning from an interplanetary mission to Earth, has been considered in the altitude range 50—120 km. Proper use of FLUENT was fixed at the free-stream Knudsen number Kn∞ < 7×10−5. Attempts have been made to increase this limit, but with no success. More specifically, a finer mesh as well as a slip velocity and temperature jump were considered. Physical conditions like the lack of isotropy of the pressure tensor and the failure of the classical phenomenological equations, both increasing with the rarefaction, are very probably the causes of the failure of FLU EN T. The basic principle of the DSMC solver is valid at each rarefaction level; a sensitivity analysis on the characteristic dimension of the cell, on the time step and on the number of simulated molecules verified that the restrictions on DS2G are imposed only by the capability of the computer. As neither experimental data nor numerical results are available at the present test conditions, the evaluation of the results relies just on qualitative considerations about the trends of experimental data, reported in the literature, of a sphere in a hypersonic transitional regime.

Numerical Methods for the Kinetic Theory of Fluids

2018 ◽  
Author(s):  
Sauro Succi
Keyword(s):  
Molecular Dynamics ◽  
Monte Carlo ◽  
Numerical Methods ◽  
Kinetic Theory ◽  
Computational Efficiency ◽  
Lattice Boltzmann ◽  
Direct Simulation Monte Carlo ◽  
Particle Methods ◽  
Direct Simulation ◽  
Simulation Monte Carlo

This chapter provides a bird’s eye view of the main numerical particle methods used in the kinetic theory of fluids, the main purpose being of locating Lattice Boltzmann in the broader context of computational kinetic theory. The leading numerical methods for dense and rarified fluids are Molecular Dynamics (MD) and Direct Simulation Monte Carlo (DSMC), respectively. These methods date of the mid 50s and 60s, respectively, and, ever since, they have undergone a series of impressive developments and refinements which have turned them in major tools of investigation, discovery and design. However, they are both very demanding on computational grounds, which motivates a ceaseless demand for new and improved variants aimed at enhancing their computational efficiency without losing physical fidelity and vice versa, enhance their physical fidelity without compromising computational viability.

Investigation of the Squeeze Film Dynamics Underneath a Microstructure With Large Oscillation Amplitudes and Inertia Effects

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
Nadim A. Diab ◽  
Issam A. Lakkis
Keyword(s):  
Rarefied Gas ◽  
Direct Simulation Monte Carlo ◽  
Squeeze Film ◽  
Dsmc Method ◽  
Inertia Effects ◽  
Flow Parameters ◽  
Fluid Behavior ◽  
Dimensionless Groups ◽  
Simulation Monte Carlo ◽  
The Impact

This paper presents direct simulation Monte Carlo (DSMC) numerical investigation of the dynamic behavior of a gas film in a microbeam. The microbeam undergoes large amplitude harmonic motion between its equilibrium position and the fixed substrate underneath. Unlike previous work in literature, the beam undergoes large displacements throughout the film gap thickness and the behavior of the gas film along with its impact on the moving microstructure (force exerted by gas on the beam's front and back faces) is discussed. Since the gas film thickness is of the order of few microns (i.e., 0.01 < Kn < 1), the rarefied gas exists in the noncontinuum regime and, as such, the DSMC method is used to simulate the fluid behavior. The impact of the squeeze film on the beam is investigated over a range of frequencies and velocity amplitudes, corresponding to ranges of dimensionless flow parameters such as the Reynolds, Strouhal, and Mach numbers on the gas film behavior. Moreover, the behavior of compressibility pressure waves as a function of these dimensionless groups is discussed for different simulation case studies.

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