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11
DSMC vs. MD and CFD in simulations of gas flows
Three alternative computational methodology
for simulations of
gas
flows
•
MD, Molecular dynamic simulations
•
DSMC, Direct simulation Monte Carlo
•
CFD, Computational fluid dynamics
Low
Moderate
High
Relative
computational cost
No limitations,
usually,
λ
/
L
< 0.1
No limitations, usually,
λ
/
L
> 0.01
Less then 1
micrometer
Typical flow length
scale
L
Continuum near
equilibrium flows
Transitional and free
molecular non
equilibrium flows
Dense gas flows,
phase changes,
complex molecules
Where applied
Dilute gas
Dilute gas
Dilute gas, dense
gas, clusters, etc.
Gas state
NavierStokes
equations
Boltzmann kinetic
equation
Classical equations
of motion for
particles
Theoretical model
CFD
DSMC
MD
L
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Stage I. Collisionless motion
X
n
= (
r
1
n
,
V
1
n
,…,
r
N
n
,
V
N
n
)
X
n
→
X
*
•
For every molecule, its equations of motion are solved for a time step
d
r
i
/
dt
=
V
i
,
m
i
d
V
i
/
dt
=
f
ei
,
i
= 1, …,
N
r
i
(
t
n
)=
r
i
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 Fall '11
 Zhigilei

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