Seminars

The plume produced by a cluster of two and four high area-ratio thrust optimized parabolic contour nozzles is visualized by way of retroreflectiveshadowgraphy. Both steady and transient operations of the nozzles (start-up and shut-down) were conducted in the anechoic chamber and high-speed flow facility at The University of Texas at Austin. The laboratory scale rocket nozzles comprise thrust-optimized parabolic contours, which during start-up, exhibit free shock separated flow, restricted shock separated flow and an end-effects regime prior to flowing full. Acoustic loads are assessed by synchronizing an eighth-inch microphone, located behind the nozzle cluster, with shadowgraphy images. Visuals of the internal flow are also provided by way of an experimentally validated RANS simulations that are compared with shadowgraphy images acquired during steady operations of the nozzles. A methodology to identify the propagation angles of the acoustic waves present on the shadowgraphy images using the Radon transform is applied. Locations in the flow where sound waves are being generated are detected. During these off design operations of the nozzles, most sound waves are generated by turbulence interactions with the shock cells located in the supersonic annular plume. During the end-effects-regime, this supersonic annular plume is shown to flap violently, thus providing a first principles understanding of the sources of most intense loads during engine ignition.