Measurement and analysis of a small nozzle plume in vacuum

Development of a Two-Way Coupled Model for Two Phase Rarefied Flows

“…A modification of the No Time Counter method of Bird 9 is used to find the number n s of computational gas molecules that are selected as potential collision partners for the particle. The value of n s is roughly given by n s ≈ N p n g πR p 2 (c r ) max ∆t/V c (11) where N p is the number of actual solid particles represented by the computation particle, n g is the number of computational gas molecules assigned to the same grid cell as the particle, R p is the effective particle radius, ∆t is the time step, V c is the cell volume, and (c r ) max is the maximum pre-collision relative speed, over a large number of time steps, for any molecule-particle pair in this cell. Note that n s must be an integer, so a probabilistic sampling method is used to round the right side of (11) either up or down such that the average values of both sides are equal.…”

“…An alternate starting point for high altitude plume simulations is the Direct Simulation Monte Carlo (DSMC) method 9 , which models the gas phase as a large collection of computational particles and makes no assumptions of continuum or quasi-equilibrium gas flow. This method has in the past been used extensively to simulate plumes from high altitude rockets or spacecraft thrusters 10,11 , and has been shown to allow for a high degree of accuracy in the characterization of gas properties in such flows. In a recent paper by Gallis et al 12 , an extension of the DSMC method is proposed to enable the simulation of rarefied flows involving a dilute and chemically inert solid particle phase.…”

Evaluation of Macroscopic Properties in the Direct Simulation Monte Carlo Method

“…widely used for solving problems from many fields, including rarefied atmospheric gas dynamics, 2 materials processing, 3 microfluidics, 4 and vacuum systems. 5 Whereas the particle representation of gas flows has enabled the DSMC method to include flow physics at the molecular level, it also gives rise to statistical fluctuations when evaluating macroscopic properties. Two related questions are therefore how to evaluate macroscopic properties and how to reduce the statistical fluctuations.…”