Monte Carlo simulation of solid rocket exhaust plumes at high altitude.

Abstract

The simulation of high altitude exhaust plumes from solid propellant rockets involves numerous complex physical processes which are not adequately understood. The work presented in this thesis aims at advancing the current state of modeling capabilities for these flows by better handling gas-solid interactions, particle rotation and shape effects, widely varying Knudsen number regimes, and radiation transport. First, using the direct simulation Monte Carlo (DSMC) method as a basis, condensed-phase particles are incorporated into the simulation of a rarefied gas flow. An existing method for the determination of momentum and energy exchange rates between a locally free molecular gas and a solid sphere is extended to nonspherical or rotating particles, by accounting for two-way coupling between the particles and gas. A nonequilibrium crystallization model for liquid Al₂O₃ droplets is also presented. A new near-equilibrium flow scheme is introduced for efficient gas phase simulation, which is shown to be well suited for DSMC-continuum hybrid two phase flow simulation. A number of Monte Carlo methods have recently been proposed for the simulation of near-equilibrium flows in a manner similar to DSMC. Based on existing methods for the ellipsoidal statistical Bhatnagar-Gross-Krook (ES-BGK) model of the Boltzmann equation, improved procedures are developed to enforce momentum and energy conservation, and to allow for rotational-translational energy exchange in a diatomic gas. In addition, a Monte Carlo ray trace (MCRT) model is developed for plume radiation analysis. Emission, absorption and anisotropic scattering are considered for non-gray condensed phase particles in a flowfield of arbitrary optical thickness. To evaluate the overall performance of the proposed schemes, simulations are performed for a representative solid rocket plume flow. Limited comparisons are made between calculated UV radiance values and measured values from a flight experiment, and relatively good agreement is found. A series of parametric studies involving simulations of this same flow is used to evaluate the influence of physical processes and input parameters related to gas-particle interaction, particle radiation, and the presence of soot. Particle accommodation coefficients and absorption index values are found to significantly influence results, while effects of soot and Al₂O₃ particle rotation are shown to be negligible.