Shock patterns in a slightly underexpanded sonic jet controlled by radial injections

This Brief Communication is focused on the shock patterns appearing in supersonic round jets subjected to azimuthal disturbances, such as those produced by discrete radial injections. First, it is highlighted that slightly underexpanded sonic jets exhibit a lens-shaped shock wave that is clearly different from the standard Mach disk. This pattern is observed in many propulsive jets. Second, when azimuthal perturbations are imposed, the shock-wave structure is shown to evolve under the action of transverse mass flows toward a pattern resembling a Mach disk configuration. An analysis of these patterns is conducted using the theory of characteristics.