Direct Simulation Monte Carlo: A Particle Method for Nonequilibrium Gas Flows. Iain D. Boyd Department of Aerospace Engineering University of Michigan Ann Arbor, MI 48109 Support Provided By: MSI, AFOSR, DARPA, NASA. Physical characteristics of nonequilibrium gas flow.
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A Particle Method for Nonequilibrium Gas Flows
Iain D. BoydDepartment of Aerospace EngineeringUniversity of MichiganAnn Arbor, MI 48109Support Provided By:MSI, AFOSR, DARPA, NASA
Direct simulation Monte Carlo (DSMC) method.
The MONACO DSMC code:
Illustrative DSMC applications:
Summary and future directions.
low density and/or small length scales;
high altitude hypersonics (n=1020 m-3, L=1 m);
space propulsion (n=1018 m-3, L=1 cm);
micro-fluidics (n=1025 m-3, L=1 m).
rarefied flow (high Knudsen number);
collisions still important;
continuum equations physically inaccurate.
Characterization ofNonequilibrium Gas Flows
u’, v’, w’
x, y, z
m, erot, evib
vehicle aerodynamics (NASA-URETI);
hybrid particle-continuum method (AFOSR);
TOMEX flight experiment (Aerospace Corp).
NEXT ion thruster, FEEP (NASA);
Hall thrusters (DOE, NASA);
micro-ablation thrusters (AFOSR);
two-phase plume flows (AFRL).
low-speed rarefied flow (DOE).
Current DSMC-Related Projects
Hypersonic flow around
a planetary probe
3D Surface geometry of
TOMEX flight experiment
1. Hypersonic Aerothermodynamics
DSMC: particle approach
uses kinetic theory
CFD: continuum approach
long length scales
solves NS equations
Of Sharp Leading Edges
Temperature Ratio (T / T∞)
Cylinder at 7.5 km/s
n=0.7 at 7.5 km/s
Shock Standoff Distance/Heat Transfer Coefficient
2. Materials Processing
3M experimental chamber for YBCO deposition
Source flux: 9.95x10-5 moles/sec
Z-component of velocity
Calculated and measured atomic absorption spectra:
– along an aperture close to the substrate symmetry line;
– at frequencies of 668 nm (left) and 679 nm (right).
Source fluxes (10-5 moles/cm2/sec)
Y : Ba :Cu = 0.84 : 1.68 : 2.52
Total Number Density
Flux (moles/cm2/s) across the substrate
orbit transfer (e.g. planetary exploration);
orbit maintenance (e.g. station-keeping);
Motivations for development of accurate models:
simulations less expensive than testing;
improve our understanding of existing systems;
optimize engine performance and lifetime;
assessment of spacecraft integration concerns.
3. Spacecraft Propulsion
SPT-100 Hall thrusters used for station-keeping;
in-flight characterization program managed by NASA;
first in-flight plume data for Hall thrusters.
u’, v’, w’
x, y, z
Beam plasma (15 deg.)
CEX plasma (77 deg.)
now a mature, well-established technique;
statistical simulation of particle dynamics;
applied in many areas of engineering/physics;
use growing due to improved computer power.
Some advantages of DSMC:
accurate simulation of nonequilibrium gas;
framework for detailed physical modeling;
can handle geometric complexity;
can be combined with other methods for multi-scale and multi-process systems.
unsteady and 3D flows;
user help: “DSMC for dummies”;
dynamic domain decomposition;
more detailed physical models.
Extensions of DSMC:
hybrid DSMC-CFD (using IP interface);
generalized hybrid DSMC-PIC;
2-phase DSMC (gas and solid particles);
speedup: implicit DSMC, variance reduction.