Aerothermochemical Analysis of Erosive Burning in a Laboratory Solid-Rocket Motor

An analysis of steady-state combustion and flow phenomena in a two-dimensional, laboratory-type solidpropellant motor is presented with emphasis on the condition of erosive burning. The problem is treated as a confined, reacting turbulent shear-flow using a second-order turbulence closure model. Low Reynolds number and propellant surface roughness effects are accounted for. Comparison of calculated results with cold flow experimental data confirms that development of the mean velocity profile is initially well described by laminar, 'inviscid theory. However, due to the rapid development of turbulence within the simulated grain-port, transition to a turbulent velocity profile is predicted to occur at center port Reynolds numbers greater than those obtained in the considered experiments. Transition of the velocity profile is theoretically found to occur prior to the onset of erosive burning in real motor environments. Comparisons of calculated results with measured static pressure distributions have been made for a composite-propellant slab motor. Good agreement with static pressure data is obtained for propellant roughness heights which are approximately 10 % of the larger AP crystal diameters, with surface roughness significantly affecting erosive burning. Theoretical comparison with the Lenoir-Robillard model also indicates that the present model predicts a much more rapid decrease in erosive burning as the port hydraulic radius is increased.