Investigation of the Characteristic Length Scale and Influencing Factors for Supersonic Gas Jets

Supersonic gas jets have been widely studied in aerospace applications, rocket engines, and hypersonic aircraft. Studying the characteristic length scale and influencing factors is of great significance for a deeper understanding of the flow characteristics of supersonic gas jets and the recognition of the target characteristics of aircraft. This paper conducts an in-depth study on the supersonic gas jet characteristics of rocket motors under ballistic missile flight conditions. By changing the three factors of nozzle pressure ratio (NPR), specific heat ratio of exhaust gasses, and co-flow velocity, the study analyzes their effects on the characteristic length scale of supersonic gas jets and explores the rules and mechanisms behind them. The results show the correlation between the NPR and the non-dimensional characteristic length scale, indicating that as the NPR increases in a logarithmic coordinate system, the non-dimensional characteristic length scale exhibits a corresponding increase. When the co-flow velocity is below the maximum velocity of the exhaust flow, the non-dimensional characteristic length scale increases with the co-flow velocity. The phenomenon is not obvious when the co-flow velocity is greater than the maximum velocity of the exhaust flow. Additionally, the specific heat ratio and air mixing degree also have a certain impact on the non-dimensional characteristic length scale.