On the subsonic near-wake of a space launcher configuration without jet

Abstract

Wake flows have been extensively investigated in the past mainly with the objective to reduce drag. The failure of Ariane 5 Flight 157 though revealed that the understanding has not been sufficient, which triggered a new series of base-flow investigations. Most of them scrutinized the dynamics of the flow at one specific point along the flight path either in the subsonic, transonic, or supersonic range. However, no coherent image of the flow topology development in terms of a parametric study is available so far. The current work addresses the question of a near-wake scaling of a generic space launcher configuration. This question is tackled experimentally by means of particle image velocimetry measurements in the vertical test section Cologne in the range of Mach 0.5, 0.6, 0.7, 0.8, and 0.9 for Reynolds numbers between Re D = 0.8 × 10 6 and 1.7 × 10 6. Results show the mean, the turbulence intensity, and the Reynolds shear stress distribution in the wake in comparison with the literature. In addition, data to the incoming boundary layer are provided and to the evolving shear layer. In that regime, the results indicate that the velocity and Reynolds stresses might be independent from the Mach and Reynolds number if scaled with the reattachment length. If this hypothesis holds true, it might be useful for the validation of numerical codes and for the initial determination of the flow field of space launchers in the design phase.

On the subsonic near-wake of a space launcher configuration with exhaust jet

“…The current study has the objective to contribute insights into the velocity field and Reynolds stress distribution over a wide subsonic range from Mach 0.5 to 0.9. The work is an extension of a preceding investigation on the exact same configuration without exhaust jet (Saile et al 2019). That study found a similar velocity and Reynolds stress distribution for the investigated flow range independently of the Mach and Reynolds number if scaled with the shear layer reattachment length.…”

“…The most dominant influence was found in the fluctuations, which are influenced by the merging shear layers from the wind tunnel nozzle and wind tunnel model. However, in the predecessor study of the current series (Saile et al 2019), this effect appeared negligible for the current experimental setup. This was attributed to the comparably large diameter ratio between the wind tunnel nozzle and the base of the model.…”

“…A classical 2D-2C PIV measurement setup was applied here which is practically equivalent to the setup described in Saile et al (2019). An Ultra CFR Nd:YAG laser system of Big Sky Laser was used.…”

“…The analysis of the images was executed with PIVview V3.60 by PIVTEC GmbH. The selection of the setting of image sampling was based on the experience and results of the preceding study without jet (Saile et al 2019). In total, a number of 345 images per run were evaluated with a window size of 32 × 16 px with an overlap of 4 × 4 px .…”

“…In other words, the question is now as following: How does the incoming boundary layer of the experiments relate to the flight? For the predecessor investigations of the same configuration without jet (Saile et al 2019), the ratio between the incoming turbulent boundary layer to the diameter of base is about 0.07 at, e.g., Mach 0.8. This is of the same order of what was approximated for Ariane 5.…”