Numerical Investigation of the Turbulent Wake of Generic Space Launchers

The turbulent wakes of generic space launchers are numerically investigated via a zonal RANS/LES method and optimized dynamic mode decomposition (DMD), to gain insight into characteristic wake flow modes being responsible for asymmetrical loads on the engine extension known as buffet loads. The considered launcher geometries range from planar space launchers up to axisymmetric free flight configurations investigated at varying free stream conditions, i.e. transonic and supersonic. The investigated wake topologies reveal a highly unsteady behavior of the shear layer and the separation region resulting in strongly periodic and antisymmetric wall pressure fluctuations on the nozzle surface. Using conventional spectral analysis and dynamic mode decomposition, several spatio-temporal coherent low frequency modes which are responsible for the detected pressure oscillations are identified. In addition, a passive flow control device consisting of semi-circular lobes integrated at the base shoulder of the planar configuration is investigated. The objective of the concept is to reduce the reattachment length and thus the lever arm of the forces as well as to stabilize the separated shear layer. The results show a significant reduction of the reattachment length by about 75%. In addition, the semi-circular lobes partially reduce undesired low frequency pressure fluctuations on the nozzle surface. However, this reduction is achieved at the expense of an increase of high frequency pressure fluctuations due to intensified small turbulent scales.