Influence of optical properties of alumina particles on the radiative heating from solid rocket plume

Abstract

The radiative properties are obtained from the optical properties of alumina particles to calculate the radiative heating from solid rocket plume. During this process, optical properties data of previous studies are reviewed and the radiative properties for a single particle are thoroughly investigated by considering particle size and temperature variation. A simple plume model is introduced to simulate the plume geometry, particle distribution that are necessary information to deduce the alumina laden plume radiative properties with temperature. The reference plume data is from KSLV-I kick motor. To calculate radiative heat flux and find the effect of optical properties on it, the plume model is again divided into two cases depending on whether the scattering effect is included or not. Discrete ordinate interpolation method is applied for radiative transfer equation solver. In the case of the plume emission only model, the optical properties including the absorption index significantly affect radiative base heating. However, when scattering is also considered, the influence of the optical properties on radiative heating is reduced due to the effect of the large scattering coefficient acting as a barrier for the optically thick condition. However, the maximum heating rate is still approximately 2.2 times larger than minimum one for the mixed case. Calculated data are from 34.2 kW/$m^2$ to 74.1 kW/$m^2$ according to the optical properties. As such, the appropriate selection of optical properties for the estimation of radiative heating from solid rocket plume is one of the most important key parameters. To determine the feasibility of this study, calculated heating are compared to the measured data obtained from the kick motor test. Although the conditions are not the same calculated heat flux data are not much far from the measured data that ranges from 43.6 kW/$m^2$ to 71.7 kW/$m^2$. This implies that the results obtained are at least reasonable to a certain extent. However, in real situation the temperature varies according to the position in the exhaust plume and the distribution of particles inside the plume is not uniform. Therefore, as future studies, investigation with more complicate plume model having variable temperature and optical parameters profiles is needed. Nevertheless, considering the discrepancy between the numerical results and the experimental results in this study, intuitively, it seems to be available that at least the preliminary design heat flux data for the thermal protection system can be obtained with simple isothermal plume model whose temperature and radiative properties from optical properties are deduced appropriately.