A study on flow characteristics of supersonic annular centripetal convergent jet subjected to different nozzle pressure ratios

The flow characteristics and physical mechanisms of supersonic free and impinging jets have been extensively studied; however, research on supersonic annular centripetal convergent jets, in which the axis of rotation is perpendicular to the flow direction, remains limited. This study presents an experimental and numerical investigation of a supersonic annular centripetal convergent jet at different nozzle pressure ratios (NPRs). The jet is radially injected into the ambient atmosphere through a precisely calibrated annular nozzle, with the Mach number at Mae = 1.88. First, the influence of NPRs on the flow structures is analyzed based on schlieren images. Annular strips appear at the exit of the annular nozzle. Supported by two-dimensional axisymmetric Reynolds-averaged Navier–Stokes numerical simulations, the observed annular strips indicate the propagation and interaction of compression and expansion waves. As the NPRs increase, the jet exhibits an increase in spacing and a decrease in the total number of annular strips. Then, the flow characteristics of the jet near the axis of rotation are analyzed. The radial jet transitions into a subsonic high-pressure flow after passing through the normal shock wave and then reaccelerates into supersonic flow along the axial direction. Finally, the physical mechanism governing the variation of compression and expansion waves with respect to NPRs in the radial jet is clarified using the oblique shock wave relations and the Prandtl–Meyer relations. As the NPRs increase, both the expansion intensity and the deflection angle at the nozzle exit intensify, resulting in a proportional increase in the scale of the shock cell.