| Abstract: | A new criterion is presented to detect global convergence to steady state,
and to identify local transient characteristics, during rarefied gas flow simulations performed
using the direct simulation Monte Carlo (DSMC) method. Unlike deterministic
computational fluid dynamics (CFD) schemes, DSMC is generally subject to large statistical
scatter in instantaneous flow property evaluations, which prevents the use of
residual tracking procedures as are often employed in CFD simulations. However,
reliable prediction of the time to reach steady state is necessary for initialization of
DSMC sampling operations. Techniques currently used in DSMC to identify steady
state convergence are usually insensitive to weak transient behavior in small regions
of relatively low density or recirculating flow. The proposed convergence criterion is
developed with the goal of properly identifying such weak transient behavior, while
adding negligible computational expense and allowing simple implementation in any
existing DSMC code. Benefits of the proposed technique over existing convergence
detection methods are demonstrated for representative nozzle/plume expansion flow,
hypersonic blunt body flow and driven cavity flow problems. |
