Numerical Simulation of Graphite Nozzle Erosion with Parametric Analysis

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Nozzle throat erosion is a major problem for solid rocket motors since it causes the degradation in the propulsive performance of solid rocket motors. The AP/HTPB composite propellants used in the rocket motors generate high concentrations of oxidizing species such as H2O, OH, and CO2 in the combustion products at temperatures ranging from 2,700 to 3,200 K for non-metalized propellants. Earlier, the authors utilized a comprehensive numerical program called graphite nozzle erosion minimization code for prediction of graphite nozzle throat erosion rates as a function of pressure and propellant composition. From these studies, it was established that various parameters affect the nozzle thermochemical erosion rate including oxidizing species concentrations, flame temperature, and operating pressure. In addition, the thermal properties of graphite could also affect the nozzle throat erosion rate since these are directly related to the surface temperature at the nozzle throat. In order to assess the relative importance of these parameters in terms of their impact on the nozzle throat erosion rate, a parametric analysis was performed in this study. Each of these parameters was systematically varied while keeping all the remaining parameters constant. Based upon this research, it is concluded that flame temperature can affect the thermochemical erosion rate most, followed by chamber pressure and major oxidizing species concentrations. The mechanisms associated with the influence of these parameters are explored and described. A comparison of predicted results with the available experimental data shows match within 20%. The parametric analysis performed in this research provides an in-depth understanding of the thermochemical erosion process and the controlling steps in the nozzle erosion phenomena.