Radiative Heat Transfer in Solid Rocket Nozzles

The radiative heat transfer within solid propellant rocket motor nozzles due to the emission and isotropic scattering by the liquid-phase alumina particles present in the combustion products is investigated. A method is presented for computing the effective absorption and scattering coefficients. The discrete ordinates method participating media radiation solver in the STAR-CCM+ code is used to compute the radiative heat flux to the nozzle wall for the HIPPO and TM-3 motor test cases. Multiple studies are performed to investigate the impact that various factors have on these calculations, including complex index of refraction, particle size distribution, exit plane radiation boundary condition, and the dimensionality of the flow and radiation solutions. The effects of boundary layers and coupling between the flow and radiation solutions are also investigated. Comparisons are made between these high-fidelity radiation solutions and simpler correlations historically used to estimate radiative heat flux in rocket nozzles; it is found that the most common emissivity correlation underpredicts radiative heat flux. Recommended methods are presented that should yield radiative heat flux predictions for rocket nozzles with increased accuracy.