Three-dimensional numerical simulation of two-phase flow in hybrid rocket motor

This paper presents the three-dimensional numerical simulation of hybrid rocket motor with hydrogen peroxide (H₂O₂) as the liquid oxidizer and hydroxyl terminated polybutadiene (HTPB) as the solid fuel. Two kinds of injector patterns are designed for the motor. The injector holes of pattern A are distributed along the projection of the fuel surface to the injector panel, and injector pattern B refers to the almost equal spaced holes design. The star fuel grain is selected for the simulation and half a star is chosen as the computational domain. The Euler-Lagrange approach is used for the two-phase flow. The droplet evaporation and decomposition, solid fuel pyrolysis, gaseous chemical reactions, and turbulence are considered in the simulation model. A series of simulation cases are performed for the two kinds of injector patterns with different droplet diameter and injection velocity. The results of the temperature contours, species mass fractions, droplet traces, fuel regression rate distributions, and combustion efficiencies are presented. For the injector pattern A, most of the droplets are injected into the fuel port and they are distributed near the fuel surface in the fuel port. On the contrary, some droplets spray directly onto the forward fuel end for the injector pattern B, and in the fuel port, the oxidizer mainly concentrates in the central area. This implies that the oxidizer and fuel of the motor with injector pattern A can be mixed better. With the increasing of the droplet diameter, the droplet residence time and distance in the combustion chamber will both increase. The increasing of the injection velocity does not affect the residence distance obviously, yet it reduces the droplet residence time with rapid velocity. In the variation range simulated, the increasing of the droplet diameter and injection velocity will both decrease the mixing of the reactants and reduce the combustion efficiency, which is more obvious for the injector pattern B. In addition, the combustion efficiency of the motor with injector pattern A is higher than that with injector pattern B, which indicates that injector pattern A may be an effective scheme in the hybrid rocket motor design.