Parametric Study of Graphite Insert Erosion

Abstract

Two identical segmented nozzles, consisting of graphite inserts and insulated with glass-fiber reinforced composites in the convergent and divergent sections, are used in the firing test at same operating condition. Due to the different thermal resistance ability, steps are formed at the interface of two materials. More specifically, the forward-facing step presents at the interface in the convergent section while the step in the divergent section is backward-facing and located at a certain distance downstream from the interface. This can be attributed to the opposite sequence of contact with the flow at the interfaces. The erosion rates, following the distribution of Reynolds number, exhibit an upward trend in the convergent section and decrease in the divergent section for both silicon phenolic and graphite. In addition, the graphite recession reaches the maximum value in the throat region. Along the cross-flow direction, the erosion rates are basically the same because the flow structure in the nozzle nearly axisymmetric. For the graphite nozzle insert, a correlation was developed in terms of chamber pressure, Reynolds number and nozzle geometry. The calculated erosion rates from the correlation showed agreement within 5% of the experimentally determined values.