Radius of curvature effects on throat thermochemical erosion in solid rocket motors

Ablative materials are commonly used to protect the nozzle housing and to provide the internal contour to expand the exhaust gases in solid rocket motors (SRM). However, erosion of ablative materials results in a throat area enlargement which reduces the chamber pressure and the thrust as well as the thrust coefficient due to the reduction of the expansion ratio. The specific impulse loss resulting from the nozzle throat erosion can be significant, especially for small-scale systems. To understand if throat erosion can be limited by suitable shaping of the nozzle contour, the present work addresses the study of the effect of the throat radius of curvature on the erosion behavior of graphite SRM nozzles for typical metallized propellants. The adopted approach relies on a validated full Navier-Stokes flow solver coupled with a thermochemical ablation model based on finite-rate chemistry. A shape change analysis is also conducted to determine how different nozzle contours are modified during the advancement of the erosion process. Results allow to quantify the overall performance increase that can be obtained by a suitable reduction of the throat radius of curvature. Copyright © 2012 by D. Bianchi, F. Nasuti and M. Onofri.