Simulation Code for Hybrid Rocket Combustion

Abstract

The simulation of the flame structure typical of hybrid rockets is addressed in this paper. The process is a complex interaction among oxidizer atomization and vaporization, gas phase combustion, fuel surface pyrolysis, soot formation and radiation phenomena. A detailed knowledge is required for the design of hybrid rocket motors and numerical simulations can be useful to improve grounding knowledge and reduce testing efforts. A hybrid flame consists of a turbulent reactive boundary layer with cross-flow blowing of gaseous fuel from the solid grain. Heat feedback from the flame sustains the combustion, being responsible for the pyrolysis of the solid fuel. The paper refers to a computational code for the simulation of hybrid flame structure and the prediction of fuel regression rate under development at the Space Propulsion Laboratory of Politecnico di Milano. The code uses a finite volume method and solves for Navier Stokes equations with RANS approach and specific combustion kinetic set. Closure terms are derived from Launder Sharma turbulence model and well stirred reactor model. Radiation is resolved through a P1 model. The computational domain is split into a solid and a gas phase region. The paper presents some typical results of the code for polybutadiene and gaseous oxygen as well as preliminary outcomes of a newly implemented two-phase flow model that simulates the combustion of aluminum drops in the core flow. Aluminum agglomerates are released in liquid state from the solid fuel surface and burn while being transported by the hot gases. The evolution of aluminum drops is derived from the Beckstead’s law. The simulation code is built on top of the open source framework OpenFOAM. A multi-domain approach is used simulating the reacting gas mixture on one side and the heat conduction in the solid fuel grain on the other.