Study of Progressivity of Multi‐perforated Solid Propellant Grains With Different Perforation Geometries

ABSTRACT To study the burning surface progressivity of solid propellant grains with progressive perforation geometries designed to reduce the sliver formation during combustion, this paper used conventional multi‐perforated grain shape geometries to compare the interior ballistics performance of traditional circular perforations with that of triangular, conical, trapezoidal and rectangular perforations. For each grain geometry, the same dimension parameters are used to make form function calculations which are later verified using parametric modelling software. Interior ballistics calculations were performed by optimizing the dimensions of perforation geometries through iterations to obtain the best muzzle velocity for each perforation geometry with a maximum permissible pressure of 320 MPa. The study confirms that reducing the number of grain slivers formed during combustion correlates with the increment of burning surface progressivity, however, such an increment in surface progressivity doesn't correspond to a better interior ballistics performance. Propellant grains with optimized combinations of conical plus circular perforations have a small increment in surface progressivity compared to traditional grains with circular perforations, which is also reflected in small differences in most parameters, including pressure and muzzle velocity. The highest surface progressivity for each grain shape was obtained from fully progressive perforation geometries which also showed the poorest interior ballistics performance with the highest pressures. The results demonstrate that, contrary to initial expectations, the formation of slivers from traditional circular perforations helps to develop a smaller maximum pressure for a certain muzzle velocity, especially when compared to fully progressive perforation geometries that don't form slivers during combustion.