Experimental Analysis on Near-Wake Flows of Space Transportation Systems

Kurzfassung

This work addresses aerodynamic issues in the near-wake of space transportation systems in the subsonic flow regime ranging from Mach 0.5 to 0.9. The activities are driven by the finding of undesired and strong buffeting loads during the ascend of Ariane 5. Thus, the flight of Ariane 5 is simulated in the Vertical Test Section Cologne at the Supersonic and Hypersonic Technologies Department, Cologne, as part of the Institute of Aerodynamics and Flow Technology at of the German Aerospace Center. Particle image velocimetry, high-speed schlieren and unsteady pressure measurements have been performed on a generic base model. The base model investigations varied with respect to the exhaust jet, the ambient subsonic Mach number and the base geometry. The analysis encompasses the mean and turbulent features of the velocity distribution and base pressure, respectively base pressure fluctuations. Further, a proper orthogonal decomposition was applied on the velocity distribution for a modal analysis of the dominant motions. The results suggest an aeroacoustic feed-back mechanism between the screeching jet noise mechanism and the near-wake flow dynamics at Mach 0.8 with running jet. This feed-back mechanism appears to introduce the highest level of turbulence if the detached shear layer from the main body reattaches on average exactly at the tip of the nozzle. If no coupling occurs, the velocity distribution appears to scale with the reattachment length over a wide subsonic Mach number range.