Numerical Investigation of the Robustness of an Axisymmetric Separating/Reattaching Flow to an External Perturbation Using ZDES

The present article focuses on the influence of an external perturbation on the dynamics and the topology of an axisymmetric separating/reattaching flow for a Mach number equal to 0.7. Zonal Detached Eddy Simulation (ZDES) is used to reproduce the flow dynamics downstream an axisymmetric backward facing step with and without a surrounding mixing layer. The instantaneous flowfield shows the influence of the outer shear layer whose structures interact with the separated flow of interest. The instantaneous flowfield depicts the scales of the two axisymmetric mixing layers. Then, the statistical properties of the flow illustrate an excellent agreement between the experiments (PIV and LDV) and the numerical simulation (ZDES). The second-order moment of the pressure coefficient unveils the very high fluctuation levels of the perturbed case compared to the unperturbed one. The analysis of the spectral content reveals a remarkable alteration of the spatial organization for the fluctuating pressure field at the wall and the normal velocity component fluctuations in the afterbody shear layer. Finally, the impact of the perturbation on the energy distribution of the afterbody unsteady side-loads is evidenced by single-point power spectral densities.