Analyzing the impact of nitrogen ejection on suppression of rocket base heating

Due to the reverse flow and recirculation caused by plumes, the base plate and nozzle external walls of a rocket suffer from severe base heating during its ascent. To protect the internal instruments from the base heating, nitrogen ejection, an active thermal protection, was adopted. The nitrogen with different total pressures and total temperatures is ejected from a tube in the base plate center to the base flow region, and its impact on the wall heat flux of the base plate and nozzle external walls is further investigated numerically. The impact of the total pressure as well as the total temperature of nitrogen ejection was analyzed numerically by computational fluid dynamics on the wall heat flux on the base plate and nozzle external walls. A density-based solver was used to solve the Reynolds-Averaged Navier-Stokes equations, and the Shear Stress Transport model was adopted to model turbulence. The results showed that nitrogen ejection can significantly reduce the rocket base heating by suppressing the reverse flow, and the base plate benefits more than nozzle external walls. As is expected, excessive total temperature increases wall heat flux. However, it is interestingly found that the wall heat flux could not decrease monotonically as the total pressure of the ejected nitrogen increases. Exceedingly large total pressure even exacerbates base heating. Therefore, it is crucial to restrict total pressure and total temperature in nitrogen ejection design. In the best case investigated, the maximum wall heat flux on the base plate and nozzle external walls was reduced respectively to 12.3% and 21.5%, and the average heat flux was reduced to 17.8% and 26.8%.