| The primary purpose of this study is to create a hybrid solver that models mixed rarefied-continuum flows efficiently. The specific motivation originates from NASA's interest in the numerical simulation of thruster plumes that evolve from the continuum to the nearly free-molecular regime. Toward this end, a 27-speed Adaptive Discrete Velocity (ADV) Euler solver has been coupled with the direct simulation Monte Carlo (DSMC) method to create a single, adaptive hybrid solver.; Novel features were incorporated within the individual ADV and DSMC algorithms. New concepts such as ghost cells, a previously unproved correction factor for the translational temperature, and the free-cell scheme were implemented in DSMC while the ADV method has been upgraded to model gases having internal rotational energy. A second step in the creation of the hybrid scheme consisted of devising a property-based coupling for information exchange at the interface. Finally, an adaptive procedure that tracks nonequilibrium regions with disconnected patches of DSMC was implemented. The degree of non-equilibrium can be quantified by appropriate breakdown parameters. Thus, the DSMC patches can be moved and deformed adaptively on a single grid to resolve complicated transient flow structures.; The one-dimensional simulations demonstrate the stability of the interface and the capability of the adaptive algorithm to capture physical phenomena such as shock waves, expansion waves and contact discontinuities. The results also show the ability of a hybrid code to maintain accuracy through the use of free-cells while utilizing relatively large sampling cells. A two dimensional algorithm was then applied to study a pressure driven impulsive jet that issues from a slit. The resulting plumes were either free or strike a simple flat plate. In addition to the macroscopic property fields, quantities of interest such as slit mass fluxes, Mach number, loads on the target plate, grid cell dimensions, number of simulated molecules, time to steady state and hardware/software characteristics are discussed herein.; The partial success of the hybrid technique in the simulation of one- and two-dimensional representative flow problems highlights its potential for the application to more complex two and three dimensional hybrid, adaptive flow simulations. |
