Numerical investigation of surface roughness effects on non-equilibrium flow in expansion section of rocket nozzle

To further understand the non-equilibrium flow characteristics in a rocket nozzle, we have to consider the rough wall surface caused by nozzle ablation, and explore the relative influence of surface roughness on the flow field, composition field, and wall heat transfer in the nozzle. In this study, first, the data of the inner wall morphology of the real nozzle is obtained through measurement experiments. The parameters used to characterize the inner wall morphology of the expansion section of the nozzle are determined. Then, a computational physical model is built based on these parameters. Finally, the simplified chemical reaction mechanism is used to solve the chemical non-equilibrium flow in the nozzle through the eddy dissipation conceptual model. The numerical calculation method of large eddy simulation is used to obtain the fine structure of the flow field with the shape of the inner wall of the expansion section of the nozzle. The results of the numerical study show that the influence of the wall roughness element of the nozzle expansion section caused by ablation cannot be ignored during the working process of the solid rocket motor. For the non-equilibrium flow in the supersonic nozzle, the roughness element is a crucial factor to promote the flow transition and the generation of hairpin vortices, and it also affects the wall heat transfer and gas composition near the roughness element.