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Computational Heat Transfer
Published in Greg F. Naterer, Advanced Heat Transfer, 2018
The Direct Simulation Monte Carlo method (or DSMC method) uses simulation molecules to represent a large number of real molecules in order to solve the Boltzmann equation (an equation describing the statistical behavior of a system not in a state of equilibrium). Molecules are moved throughout the physical domain in a manner that is coupled with the appropriate time and length scales. Molecular movement and collisions are decoupled over time periods less than a mean collision time. Collisions among the molecules and between molecules and walls are calculated based on probabilistic models. Examples of common collision models include the Hard Sphere Model (HSM), Variable Hard Sphere Model (VHSM), and Variable Soft Sphere Model (VSSM). The DSMC method is commonly applied to problems involving spacecraft reentry aerodynamics and micro- and nano-electromechanical systems. It is a powerful method for the computation of complex, nonequilibrium gas flows, such as hypersonic flows where nonequilibrium conditions occur at high altitude and in regions of small length scales. Boyd (2015) presented a comprehensive overview of the theoretical basis of the DSMC method.
Introduction
Published in Mohamed Gad-el-Hak, MEMS, 2005
In this chapter molecular-based simulation methodologies for liquid and gas flows in micron and submicron scales were presented. For simulation of gas flows, the main emphasis was given to the direct simulation Monte Carlo (DSMC) method. Its algorithmic details, limitations, advantages, and disadvantages were presented. Although the DSMC is quite popular for analysis of high-speed rarefied gas flows, it is not as effective for simulation of gas microflows. It suffers from slow convergence and large statistical noise, and it requires an extensive number of simulated molecules. These disadvantages can be eliminated to some degree by using the newly developed information preservation (IP) technique. However, the IP-DSMC is still undergoing development and validation. An alternative to the DSMC method is solution of the Boltzmann transport equation, which is an integro-differential equation with seven independent variables. It is clear that the Boltzmann equation algorithms are very complicated to implement for general engineering applications, but they can be used for simple geometry cases, such as in microchannels. A final alternative for simulation of gas microflows is the lattice Boltzmann method (LBM), which has been developed extensively within the past decade. The LBM has relatively simpler algorithms that can handle both the rarefied and continuum gas flows from a kinetic theory point of view, and the ability of the LBM to capture the incompressible flow limit can make this method a great candidate for microfluidic simulations.
Numerical Chapter
Published in James J Y Hsu, Nanocomputing, 2017
The direct simulation Monte Carlo (or DSMC) method is widely used for the modeling of gas flows by computating the motion of the representative molecules, instead of solving the Navier-Stokes equation.This isnecessary for a “rarefied” flow whose essential characteristics namely, the molecular mean free path is not negligibly small than the physical dimensions of micro or nano scale.
Effect of Thermal Ablation at the Fluid-Solid Interface of a Hypersonic Reentry Vehicle in Rarefied Flow Regime
Published in International Journal of Computational Fluid Dynamics, 2021
The high-speed reentry flows considered in this work are simulated using SPARTA (Stochastic PArallel Rarefied-gas Time-accurate Analyser) developed at Sandia National Laboratories (Plimpton et al. 2019). It is a parallel direct simulation Monte Carlo (DSMC) code capable of performing simulations of rarefied gas flows in 2-D or 3-D. It can be run on single or parallel processors by spatially decomposing the simulation domain and using message-passing interface (MPI) techniques. The code is open-source and can be easily modified or extended based on user requirements. Conventionally, the DSMC solvers use line segments and surface triangulation to represent 2-D and 3-D objects, respectively. The input script for the code is modified to account for the non-uniform wall temperature boundary condition for the flow solver so that the effect of wall temperature on the flow properties can be studied. Flow simulations in this work are carried out using parallel 2-D SPARTA code (Plimpton et al. 2019) with 40 Intel Xeon E5-2670V3 processors.
HALO3D: An All-Mach Approach to Hypersonic Flows Simulation
Published in International Journal of Computational Fluid Dynamics, 2022
Vincent Casseau, Wenbo Zhang, Shrutakeerti Mallikarjun, Wagdi G. Habashi, Song Gao, Abolfazl Karchani
Toward this end, a few multiphysics models have received considerable attention: The conservative form of the Navier-Stokes (NS) equations for weakly-ionised near-continuum hypersonic flows has been reviewed at length in (Anderson 2006; Barbante and Magin 2004; Boyd and Schwartzentruber 2017; Candler and Nompelis 2009; Gnoffo, Gupta, and Shinn 1989; Gupta et al. 1990; Lee 1984).The two-temperature model of Park (Park 1990, 1993) has been routinely employed to model vibro-electronic non-equilibrium, with its three-temperature counterpart featuring either rotational (Holman and Boyd 2009) or electronic non-equilibrium (Kim, Gülhan, and Boyd 2012) seldom considered.Gas surface interactions, whereby atomic species being carried through the shock layer may recombine on the craft's surface, have been accurately modelled via a finite-rate surface chemistry species boundary condition in (Alkandry, Farbar, and Boyd 2012; Farbar et al. 2014; Marschall and Maclean 2011).Its extension to model surface ablation is presented in (Farbar, Anna, and Boyd 2015; Martin and Boyd 2015), where a transient material response code, responsible for heat conduction through the thermal protection system (TPS), is loosely coupled to a continuum solver.The interaction of weakly ionised gases and magnetogasdynamics (MGD)-based devices in applications such as aerodynamic control, blackout mitigation and thermal protection has been modelled by coupling the Maxwell equations and the gas dynamics equations under the magneto-hydrodynamics (MHD) assumptions (Khan, Hoffmann, and Dietiker 2007; Thompson et al. 2015).In atmospheric reentry simulations where natural ionisation is the only source of charged particles, the low-magnetic Reynolds number formulation that omits the induced magnetic field has been found satisfactory (Gaitonde 2004).For the upper atmosphere, the foremost approach to simulate rarefied flow fields is the Direct Simulation Monte Carlo (DSMC) method (Bird 1994), which traces a large number of particles deterministically and treats collisions stochastically. Similar to CFD for continuums, it asymptotically provides an exact solution to rarefied gases as the number of simulated particles tends to infinite with the time step and cell size are tending to zero (Wagner 1992). In addition, the method offers the possibility to be seamlessly coupled to continuum solvers (Espinoza 2018; Verhoff and Boyd 2012) using buffer regions at the NS-DSMC interface.