Immersed boundary method and centered scheme for the study of aero-acoustic field in SRMs

A monolithic aft-finocyl Solid Rocket Motor is characterized by a propellant grain with a cylindrical core and a final star-shaped region located close to the thrust nozzle. This peculiar geometry of the pro- pellant grain can induce significant effects on the combustion chamber pressure field that can exhibit an unsteady behavior for some typical time windows of the operative life of the motor. At the present state of the art, the coupling of hydrodynamic instabilities and chamber acoustics is supposed to be the main responsible of pressure oscillations onset. The paper aims to investigate the possibility to study the aeroa- coustic problem in aft-finocyl SRMs by means of 3D unsteady CFD simulations performed by using a new 2 nd hybrid self-adjusting centered scheme. An immersed boundary method is employed for the boundary treatment. The new numerical method, along with the immersed boundary technique, is validated by sim- ulating a Taylor-Culick flow and a Laval nozzle. Then the numerical method is applied to a simplified aft-finocyl solid rocket motor showing the capability of the code to characterize pressure oscillations at limit cycle conditions.