Two-phase turbulent flow interactions in a simulated rocket motor with acoustic waves

A numerical study of two-phase turbulent flows in a simulated solid rocket motor with acoustic oscillations has been carried out. The main purpose is to study the interactions between particle dynamics and gas-phase flowfield in an oscillatory environment and on this basis to further explore the particle effects on combustion instability in a solid rocket motor. The physical model consists of an axisymmetric chamber with a closed head end. As a first approach, premixed gas and particle mixtures are injected into the chamber through the side walls to simulate the evolution of combustion products from solid propellants. Aluminum particle is selected in this work due to its extensive use as combustion stabilizer in practical solid rocket motors. Periodic pressure oscillations are imposed at the exit to simulate acoustic standing waves in the chamber. The analysis is based on a two-phase flow model in which the Eulerian approach is used for the gas phase. The coupling between the two phases are treated by adding appropriate source terms in the gas-phase conservation equations. The Lagrangian approach is employed for the particle phase in order to resolve detailed particle dynamics. The numerical technique for the gas phase is based on a preconditioning technique previously developed to overcome computational difficulties for chemically reacting flows at low Mach numbers. Results in the present study show that turbulence kinetic energy follows the sinusoidal motion but with different phase compared with the mean velocity. An oscillatory flow may provide additional mechanisms to transfer kinetic energy from periodic motions to turbulence flow, and consequently may increase turbulence intensity in various parts of the chamber. On the other hand, the shear waves arising from acoustic oscillations are substantially damped because of the turbulence-enhanced viscous effects. As a result, the acoustic waves in the turbulent flow exhibits a 1-D pattern except in the near-wall region. Observations of particle trajectories reveal a strong turbulence effect on particle dispersion.