Numerical analysis of radiative heat transfer in rocket engines

Thermal radiation represents a fundamental, yet often underestimated or missmodeled, mode of heat transfer in rocket engines. The extreme thermodynamic conditions encountered in combustion chambers—characterized by high temperatures, pressures, and the presence of radiatively active species and particles—make radiative effects potentially comparable to convective heat fluxes. However, the lack of models validated for rocket engine environments has limited their inclusion in predictive simulations. This thesis addresses this gap through a comprehensive numerical analysis of radiative heat transfer across liquid, hybrid, and solid rockets. A general framework for radiation modeling was developed, solving the radiative heat transfer equation in absorbing, emitting, and scattering medium with the discrete transfer method. Several spectral and global approaches for gaseous radiative species have been implemented, along with dedicated models for particulate radiation. The solver was coupled to CFD simulations of reactive, turbulent, compressible flows for different propulsion systems. For liquid rocket engines, the analysis compared several gas radiation models for oxygen–hydrogen and oxygen–methane propellant combinations under chamber conditions up to 100 bar. The results showed the need for radiation models specifically tailored for LRE conditions. Reduced-order WSGG models were developed and validated, offering substantial computational savings while maintaining good accuracy with respect to detailed spectral methods. For hybrid rocket engines, a detailed investigation of gas and soot radiation was carried out in an oxygen–HTPB motor. Simulations revealed that soot emission can represent a major fraction of the radiative heat flux and significantly affect the fuel regression rate, improving the agreement with experimental data. For solid rocket motors, radiation from alumina particles was modeled, accounting for absorption, emission, and scattering effects. Results highlighted that scattering anisotropy and particle size distribution strongly influence the wall heat flux, which can locally exceed the convective contribution in the nozzle throat. Overall, this work bridges the gap between radiative transfer modeling and rocket engine analysis, providing validated tools and physical insight into the role of radiation in propulsion system design.