Flow and Acoustics of Clustered Rockets During Startup

Abstract

The plume produced by a cluster of two large-area-ratio thrust-optimized parabolic contour nozzles is visualized over a range of nozzle pressure ratios by way of retroreflective shadowgraphy. Both nozzles exhibit free-shock separated flow, restricted-shock separated flow, and an end-effects regime before flowing full. Transient (startup) operations of the nozzles are studied, with the primary focus being the pulsations that form during the end-effects regime. This occurs at a pressure ratio of 37 for these nozzles and is associated with elevated sound levels in the immediate vicinity of the nozzles and vehicle. The shadowgraphy images reveal the formation of turbulent large-scale structures, on the order of the nozzle diameter, during the end-effects regime. These large-scale structures are driven by the intermittent opening of the last trapped annular separation bubble to the ambient and grow rapidly within the first two nozzle diameters.