Numerical study on the effect of multi-hole injector on three-dimensional flow and heat transfer properties of a novel combined solid rocket motor

The injection mode of oxidizer gas significantly affects the flow and heat transfer characteristics of rocket motors with separated oxidizer and fuel propellants. In the present study, the effect of the multi-hole injector on flow and heat transfer of a novel combined rocket motor is studied with a three-dimensional numerical model. The results show that as the number of injection holes increases from one to five, muti-jet interference effect could occur. The original single coupled combustion zone is split into multiple coupled combustion zones. Multi-peak distributions of temperature and velocity are thus observed. As the combustion heat release is gradually advanced towards the injector, the multiple injection flows form three high-flow velocity zones. The three-dimensional distribution of heat transfer coefficient is highly consistent with that of flow velocity. The average heat transfer coefficient first increases and then decreases with the increase in the number of injection holes. The 4-hole injector renders the largest average heat transfer coefficient. Due to the multi-peak distribution of flow velocity and heat transfer, a multi-peak distribution of regression rate for solid propellant is thus observed. The average regression rate increases greatly and reaches the maximum value for the 4-hole injector. The results also show that the regression rate is controlled by the combustion reaction kinetics in the proximal injector region but is controlled by heat transfer in the region far away from injector. The present study contributes to a better insight into the flow and heat transfer effects on combustion performance of the combined solid rocket motor with multi-hole injector.