Numerical Analysis of the Turbulent Wake for a Generic Space Launcher with a Dual-Bell Nozzle

The turbulent wake of an axisymmetric generic space launcher equipped with a dual-bell nozzle is simulated at transonic (\(Ma_\infty = 0.8\) and \(Re_D = 4.3\cdot 10^5\)) and supersonic (\(Ma_\infty = 3\) and \(Re_D = 1.2\cdot 10^6\)) freestream conditions, to investigate the influence of the dual-bell nozzle jet onto the wake flow and vice versa. In addition, flow control by means of four in circumferential direction equally distributed jets injecting air encountering the backflow in the recirculation region is utilized to determine if the coherence of the wake and consequently, the buffet loads can be reduced by flow control. The simulations are performed using a zonal RANS/LES approach. The time-resolved flow field data are analyzed by classical spectral analysis, two-point correlation analysis, and dynamic mode decomposition (DMD). At supersonic freestream conditions, the nozzle counter pressure is reduced by the expansion of the outer flow around the nozzle lip leading to a decreased transition nozzle pressure ratio. In the transonic configuration a spatio-temporal mode with an eigenvalue matching the characteristic buffet frequency of \(Sr_D=0.2\) is extracted by the spectral and DMD analysis. The spatial shape of the detected mode describes an antisymmetric wave-like undulating motion of the shear layer inducing the low frequency dynamic buffet loads. By flow control this antisymmetric coherent motion is weakened leading to a reduction of the buffet loads on the nozzle fairing.