Refractive index field of a solid-propellant rocket jet by Background-Oriented Schlieren

This work demonstrates the use of high-speed, single-camera Background-Oriented Schlieren (BOS) as a robust diagnostic tool for characterizing reactive, high-temperature supersonic jets issued from a non-aluminized solid-propellant rocket motor (SRM). Tailored to handle strong optical deflections and intense plume luminosity exacerbated by after-burning, the BOS system yields relevant quantitative reconstructions of axisymmetric mean refractive index fields in the stable regime of the SRM, when corrected for deflection drifts induced by plume disturbances. The resulting dense, large-field measurements capture key quantitative features of two distinct SRM plumes, one in isolated operation and one with a supersonic co-flow. Supported by an uncertainty analysis, these reconstructed fields provide a valuable benchmark for assessing the performance of corresponding numerical simulations.