Rocket Nozzle Cold-Gas Test Campaigns for Plume Investigations

Kurzfassung

Within a joint research effort of Astrium and DLR, cold-gas test campaigns with subscale nozzles were performed to investigate a) the wall heat flux for separated nozzle flows, and b)the plume pattern for an overexpanded supersonic free-jet nozzle flow. For both test campaigns, a thrust-optimized, parabolic nozzle was the subject of investigation. This type of rocket nozzle, frequently used in the Western world for rocket engines, features two separation patterns during start-up and shut-down, or for engine operation with chamber pressures not sufficient to reach full-flowing in the nozzle extension, the classical free shock separation and restricted shock separation. The objective of both test campaigns was the investigation of the wall heat transfer in both separation patterns, and the investigation of the cap-shock pattern which special emphasis on the partly subsonic core vortex at the centreline. Wall temperatures were measured by infrared thermography, showing that a local heat flux increase is observed in the incipient separation. Furthermore, the formation of vortexes near the wall was observed. For the plume investigation, the core vortex was resolved by means of threads and laser induced grids. Experimental results for the core vortex position were compared with numerical flow field analyses.