Secondary instabilities in swept-wing boundary layers: Direct Numerical Simulations and BiGlobal stability analysis

View Video Presentation: https://doi.org/10.2514/6.2022-2330.vid

The evolution of secondary instabilities in a three-dimensional stationary-crossflow-domina- ted boundary layer is investigated by means of Direct Numerical Simulations (DNS) and linear spanwise BiGlobal stability analysis. Single-frequency unsteady disturbances and a critical stationary crossflow mode are considered. Unsteady perturbation content at 1 kHz manifests in the form of the type-III secondary instability mechanism in the lower portion of the boundary layer in the both the DNS and the stability approach. Considering disturbances at 6 kHz, the results from the stability analysis reveal the existence of largely amplified type-I and type-II secondary instability mechanisms. Strong growth displayed by the former is measured in the DNS, which potentially overshadows manifestations of the type-II mechanism. Laminar- turbulent transition primarily induced by the growth of type-I disturbances is captured in the 6 kHz case. Overall, we report good agreement between DNS and stability analysis in terms of perturbation organization and growth rate for all cases studied.