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

Abstract

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.

Investigations on the turbulent wake of a generic space launcher geometry in the hypersonic flow regime

“…13). A periodicity in this range is also seen in [10] for a higher unit Reynolds number of 16 · 10 6 m −1 with the same wind tunnel model and various nozzle diameters. The numerical simulations calculated the recompression shock to be further downstream than measured in experiments (see Fig.…”

“…Despite the ambiguous information from the incoming boundary along the main body, the investigated case shows strong similarities to the case described in [10] with a turbulent boundary layer and a Reynolds number of 16 · 10 6 m −1 and comparisons will be made later in this section. The pressure spectra reveal that the internal §ow dynamics and the §ow topology of the recirculation zone undergoes a crucial change when a nozzle is attached to the base region.…”

“…A detailed overview to the methods applied is described in [10]. Most of the measurement methods are identical.…”

Experimental and numerical investigation of the turbulent wake flow of a generic space launcher configuration

“…Regarding the chosen similarity conditions, it can be stated that the shear layer expansion and subsequent recompression, which, as will be shown in section 5.1, plays the dominant role in the wake at Ma ∞ = 6, are considered similar to a real §ight. Former investigations, e. g., by Murthy [15], have shown that the Reynolds number has little in §uence on the base pressure/pressure ratio as long as the incoming boundary layer is turbulent, which is the case for the current §ow problem as was shown by Saile et al [16]. The shear layer expansion is, mainly, a function of the Mach number.…”

“…Note that the mean shear layer expan- Figure 11 Standard deviation of a sequence of high-speed schlieren images of the recompression shock exemplary for the dummy nozzle con¦guration [16] sion angle β s is approximately alike for both afterbodies (β e ≈ 26 • ), which indicates a nearly equal base pressure level being proved in subsection 5.2. Finally, to validate the numerically computed §ow ¦eld topology, the time-averaged positions of the recompression shocks detected experimentally by Saile et al [16] using high-speed schlieren measurements, an example of which is shown in Fig. 11 for the nozzle dummy con¦guration, are drawn in Fig.…”