Study of Liquid Breakup Processes in Solid Rocket Motors

Abstract

In a solid rocket motor (SRM), when the propellant combusts, the aluminum is oxidized into alumina (Al 2 O 3 ) which, under the right flow conditions, tends to agglomerate into molten droplets, impinge on the chamber walls, and then flow along the nozzle wall. Such agglomerates can cause erosive damage. The focus of the current research is to characterize the agglomerate flow within the nozzle section by studying the breakup process of a liquid film that flows along the wall of a straight channel while a high-speed gas moves over it. We have used an unsteady-flow Reynolds-Averaged Navier-Stokes code (URANS) to investigate the interaction of the liquid film flow with the gas flow, and analyzed the breakup process for different flow conditions. The rate of the wave breakup was characterized by introducing a breakup-length-scale for various flow conditions based on the Volume Fraction (VF) of the liquid, which is an indicator of a two-phase flow liquid breakup level. A smaller breakup-length-scale means that smaller drops have been created during the breakup process. The study covers the breakup and fluid behaviors based on different gas-liquid momentum flux ratios, different surface tension and viscosity settings, different Ohnesorge numbers (Oh), and different Weber numbers. Both water and molten aluminum flows were considered in the simulation studies. The analysis demonstrates an effective method of correlating the liquid breakup with the main flow conditions in the nozzle channel path. Nomenclatureg = gravity K = temperature in Kelvin L = characteristic length of the droplet P = pressure T = temperature t = time = time averaged fluctuating velocity component in Reynolds Stress Model v, V = general velocity expression Oh = Ohnesorge numbers Oh= √ / Re Re = Reynolds number Re=ρvL / μ We = Weber number We=(ρv 2 L) / σ Symbol = alumina temperature correlated density parameter = thermal expansion coefficient = temperature in Reynolds Stress Model = viscosity = density of fluid a Distribution A (