Solid rocket motors (SRM) are extensively employed in satellite launchers, missiles and gas generators. Design considers propulsive parameters with dimensional, manufacture, thermal and structural constraints. Solid propellant geometry and computation of its burning rate are essential for the calculation of pressure and thrust vs time curves. The propellant grain geometry changes during SRM burning are also important for structural integrity and analysis. A computational tool for tracking the propagation of tridimensional interfaces and shapes is then necessary. In this sense, the objective of this work is to present the developed computational tool (named RSIM) to simulate the burning surface regression during the combustion process of a solid propellant. The SRM internal ballistics simulation is based on 3D propagation, using the level set method approach. Geometrical and thermodynamic data are used as input for the computation, while simulation results of geometry and chamber pressure versus time are presented in test cases.
TopIntroduction
Rockets based on chemical energy (with solid or liquid propellants) are currently the only means to access Space and research and development of this area has vital importance for Aerospace Engineering. The Brazilian Aerospace Program has a long history using Solid rocket motor (SRM) technology since the sounding rocket Sonda I launched in 1965 (AEB, 2017). In this context, the reduction of project costs with modern computational simulations is an important interest of the involved companies and institutes.
Solid rocket motors are employed in satellite launchers, missiles and gas generators. The design takes on account propulsive parameters such as thrust versus time, with dimensional, manufacture, thermal, structural constraints. Experiments using real scale rocket models are costly, therefore computational simulations are required to decrease the overall project cost.
The combustion mechanisms for solid rocket propellants are quite complex and dependent on many local fluid, chemical, and thermal phenomena. Many solid rocket propellant burning-rate models are greatly simplified because of limited computational power and understanding of the combustion process (Wiedemanna, et al., 2009). In the exhaust gas of typical SRM engines, a considerable amount of small aluminum oxide particles is included. Aluminum is used as an additive in the motor propellant in order to increase performance and to dampen burn instabilities. During the burn process, most of this aluminum is transformed into aluminum oxide. A large number of micron-sized dust particles are generated continuously during a burn. At the end of a burn, a second group of much larger fragments from a slag pool clustering inside the motor leaves the nozzle.
There are several quasi-steady formulations to predict the burning rate of an energetic solid material. One of them is the Vieille’s or Saint Robert’s law (Marmureanu, 2014), which is an empirical model that represents the pressure dependence on burn rate, as will be shown further on.
Solid propellant geometry and modeling of its burning are essential for calculation of pressure versus time and thrust versus time curves (NASA, 1971). In addition, propellant structural integrity is mandatory during the rocket burn. Structural analysis use propellant geometry as input and should consider the burning surface regression, i.e., the propellant grain geometry changes during rocket burn. A computational tool for tracking the propagation of tridimensional interfaces and shapes is necessary for this task. This developed tool for SRM burning simulation (named RSIM) handles complex grain geometry for versatility. Figure 1 presents the design flowchart.
Solid Rocket Motor History in Brazil
The Brazilian Aerospace Program has a long history using SRM technology since the sounding rocket Sonda I (1965). In this context, the reduction of project costs with modern computational simulations is an important interest of the involved companies and institutes.
Figure 2.
VLS launch trajectory (IAE, 2012)
Figure 3.
Brazilian sounding rockets, (AEB, 2017)