A simulation of the flow near a burning propellant in a solid propellant rocket motor

An investigation has been conducted related to the velocity coupling phenomenon reported in acoustically unstable solid propellant rocket motors. An innovative simulation facility has been built using solid carbon dioxide as the simulated propellant. The use of dry ice allows us to focus directly on the fluid mechanical aspect of the problem.; Mass flow rate and acoustic pressure measurements indicate the existence of a coupling mechanism, strongly dependent on velocity amplitude, between the acoustic disturbance and dry ice sublimation process. Flow visualization and hot film anemometry both indicate the occurrence of turbulence in the case of strong acoustic excitation. Transition near a velocity antinode appears to be associated with shear instability, while transition near a velocity node has also been observed and appears to be influenced by the strong velocity gradient or any initial disturbances. Study of the velocity signal indicates that turbulence is probable to have occurred during only part of oscillation cycle as the flow always recovers to be laminar during the same cycle. Acoustically induced turbulent forced convection is believed to be responsible for the increase in the sublimation rate of the dry ice (simulated burning of the propellant). Comparison with previous experiments conducted with real solid propellants shows striking similarity in the energy transfer mechanism. An empirical correlation was developed that showed the turbulent heat convection rate was dependent on the ratio of an acoustic Reynolds number to the 0.8 power. These experiments lead one to believe that turbulence is one of the principal mechanisms in the velocity coupling phenomenon.