Particle Simulation of Gas Expansion and Condensation in Supersonic Jets

Abstract

The direct simulation Monte Carlo (DSMC) method is used to simulate the flow created prior to formation of a Z-pinch in the Nuclear Weapons Effects (NWE) Decade facility at the Arnold Engineering Development Center (AEDC). The simulation domain and the inflow boundary conditions are determined on the basis of a continuum-based Computational Fluid Dynamics (CFD) analysis. The DSMC simulation shows that the rapid expansion of the argon gas in the dual shell, concentric annular nozzle leads to large supersaturated regions. A homogeneous condensation model is then proposed for the DSMC simulation to include the effects of the nucleation and condensation, which explains the principal differences between the simulation results and available experimental data.

Improved sampling techniques for the direct simulation Monte Carlo method

“…6a where the percentage of one energy in the total is E a /(E a + E b ). Clearly, the modified procedure improves greatly the numerical efficiency when n a is much smaller than n b , which is usually the case for complicated molecules such as clusters having many atoms [6]. Numerical tests also show that the commonly used procedure can accept unusual values with a relatively large probability.…”

“…However, many attempts have to be made to sample a value when n a and n b are not of the same order of magnitude [6]. Here we propose a remedy to avoid finding x itself by converting x to a new variable y whose statistical value is close to 0.5.…”

Modeling Gas Nucleation and Condensation Using the Direct Simulation Monte Carlo Method

“…We combine the condensation and evaporation probabilities into one probability, and use the sign of the combined probability to indicate a possible nucleation or condensation event. The combined condensationevaporation probability is derived as: (22) Note that the post-collision status is determined only for a condensation event. The status for an evaporation or reflection event is not determined.…”

“…Therefore, the DSMC method is becoming a popular approach for model testing and flow investigation. 11,[18][19][20][21][22] For instance, Hettema and McFeaters 11 used the DSMC method to implement the Smoluchowski approach; Zhong et al 21 employed the classical nucleation theory in the DSMC method studying supersonic plumes. Most of these applications, however, have neglected the cluster effects on gas flows, which then affects the cluster modeling.…”

“…23 We also showed the clustering effects on gas flow in our previous paper when studying gas expansion in a supersonic nozzle by including dimers in the simulation. 22 However, there is no systematic nucleation and condensation model developed for the DSMC method yet.…”