Numerical simulation of chemical erosion in Vega solid-rocket-motor nozzles

The erosion of rocket-nozzle ablative thermal protection materials during the solid-rocket-motor burning time needs to be accounted for to get reliable performance predictions, especially for long-duration firings and/or small nozzles (that is, upper stages). This work numerically investigates the erosion behavior as a function of chamber conditions for the nozzles of the Vega launch vehicle solid rocket motors: Zefiro 9, Zefiro 23, and P80. This study has been performed using a Reynolds-averaged Navier–Stokes equation solver with specific application to ablative nozzles. The throat region of the nozzle, and specifically the carbon/carbon nozzle insert, has received special attention because its evolution has a significant impact on the motor performance. The analysis of the throat insert has been performed for the three full-scale nozzles by comparing the predictions to measured data from static firing tests. A sensitivity analysis to the most important model parameters that can influence the throat erosion prediction has been performed to highlight modeling capabilities and limits, as well as numerical uncertainties. Finally, a characterization in terms of nozzle throat ablation mass flux dependency upon the motor chamber pressure has been derived for the three nozzles via a power fitting of the numerical data performed at discrete chamber pressure levels.