Rapid Computational Fluid Dynamics Method for SRM Grain Design using the Geometric Immersed Boundary Condition Method

Propellant grains used in solid rocket motors (SRM) are characterized by complex three-dimensional (3D) geometries developed from primitive two-dimensional shapes. The grain area profile coupled with a propellant burn rate generates the mass flow to deliver the required thrust. Modern numerical methods promise an increase in both computational speed and accuracy for the analysis of solid propellant rocket motor. The prediction of the 2D axial-symmetric and 3D inviscid flow takes into account the evolution of the propellant grain burn surface as well as the multiphase flow of gas in the grain port. These simulations have been extended to the analysis of viscous, turbulent gas flow and the simulation of solid propellant rocket motor during operation in the normal and the abnormal operating conditions. A problem remains in the coupling of the time-dependent motor internal ballistics to the evolution of grain burn surface during combustion. For these applications, the method has to compute the flow in a time-dependent domain and the method has to track the grain surface with a burning rate depending on local flow properties. The coupled problem is complex and the primary contributor to this complexity is the deformation required in the computational for arbitrarily complex 3D geometries. Many of the methods currently used are either inflexible and time-consuming or computationally very expensive. This paper describes a coupled 3D simulation capability for the design and analysis of SRM’s using the Finite Volume Method to determine the flow-field coupled with a novel burn surface treatment based on geometric immersed boundary conditions.