Investigations on the Near-Wake Region of a Generic Space Launcher Geometry

The near-wake of a separated flow behind a generic space launcher model with different afterbody extensions is studied experimentally in the hypersonic flow regime (Mach number 6.0 and unit Reynolds number 16×10^6 m−1) with the main objective being to show unsteady flow phenomena. This objective is based on the desire to control the base flow of space launchers to reduce drag and dangerous vibrations. The investigations focus on the unsteadiness of the base-pressure fluctuations and the oscillations of the recompression shock. Base-pressure spectra and spectra of the vertical recompression shock oscillation are discussed for various pressure transducer locations, various nozzle lengths and nozzle diameters. The base-pressure spectra exhibits dominant Strouhal numbers centered at 0.08 at the center positions and 0.08, 0.2, 0.38 at the outskirts of the base, and shows a crucial change with a frequency shift to Strouhal number of 0.27 when a nozzle is applied. Additionally, the pressure spectra indicate an azimuthal mode. The spectra of the recompression shock feature a dominant Strouhal number of 0.2 independent of the geometry of the afterbody. Since the incoming boundary layer is suspected to have an influence on the near-wake flow, the state and the flow conditions are examined in introductory experiments by means of infrared images of the model surface and Pitot pressure at the body corner