A numerical simulation for prediction of thermal ablation in composite rocket motor casing

Abstract

Thermal protection systems (TPS) are used in space applications to protect structures failing from burning and/or excessive temperatures. In this work, a finite element simulation is performed to analyze the behavior of a composite rocket motor casing during the expansion of combustion gases inside the motor. A two-dimensional axisymmetric model of a rocket motor casing provided with an insulating liner is modeled in a finite element software ANSYS. Variable equivalent heat flux at the inside faces of the liner, due to radiation and convection of gases, is estimated and applied as a boundary condition. The reduction of heat load with time due to latent heat of fusion and the resistance offered by char that exists above the pyrolysis front is also considered. At the same time, the material properties of the portion of the liner exposed to its melting point temperature are regulated to offer negligible resistance to move the boundary load on to the pyrolysis front at every instant. A transient analysis is carried out with appropriate mesh quality and time steps for 10 s. Ablation, charring, and unaffected regions are identified and the required insulation liner thickness is recommended. Extension of the procedure to model a similar motor with any other cylindrical length is discussed.