Experimental and numerical analysis of the slag entrapment in Ariane 5 solid rocket motors

Abstract

The accumulation of alumina is an inherent problem in Solid Rocket Motors (SRM). In the V on Karman Institute this problem have been studied using a scale model of Ariane 5 booster where alumina is modeled with water. The Stokes number is maintained. After a parametric test, the relevant parameter found to be responsible for the entrapment of particles, was the horizontal distance between the tip of the isolation ring (inhibitor) and the nozzle tip. This parameter is named as Obstacle tip to Nozzle tip (OT2NT). The problem found during Tóth investigation was that a large part of the water accumulation in the cavity was due to the dripping of the inhibitor. The rst objective of the experimental part have been to reduce the dripping modifying the inhibitor design. The design found to minimize the dripping is the one with no extra absorbing material and a wider top plate (24mm). A posteriori, a parametric tests was done. OT2NT has been con rmed to be the main responsible while the entrapment for the new system is around a half of Tóth results. The aim of the numerical part have been to apply an existent code, Open-Foam twoPhaseEulerFoam library, based on the nite volumes. Then this code have been modi ed in order to handle with ve dispersed phases with different properties, named as sixP haseEulerFoam. The codes have been verificated through a direct comparison with existing publications. Then a sensitivity study to numerical parameters has been done. For twoPhaseEulerFoam it has been found than the results are close to the existing ones while for the sixP haseEulerFoam although the behavior of the solution is the one expected, its values are overestimated giving only a qualitatively valid answer to the problem. Finally, twophaseEulerFoam is applied to the booster geometry studied in the experimental part. Due to the fact that OT2NT has been determined as the main responsible for the entrapment, three different geometries showing three different OT2NT (25:69, -4:31 and -25:91 mm) values have been tested. It was found that for positive values, nozzle over the inhibitor tip, the entrapment increases while it decreases for negative values (the same behaviour than found in the experiments).