Casacuberta, J., Groot, K.J., Hickel, S., Kotsonis, M. (2022)
SciTech Forum and Exposition, San Diego. AIAA paper 2022-2330, doi: 10.2514/6.2022-2330

The evolution of secondary instabilities in a three-dimensional stationary-crossflow-dominated 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 instability mechanism in the lower portion of the boundary layer in 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.


Chordwise evolution of the stationary crossflow perturbation from DNS (lines), linear PSE (white symbols), and non-linear PSE (blue symbols).
Type III unsteady perturbation field from DNS (color map) and BiGlobal stability analysis (green lines). The black solid lines visualize the distorted steady base flow.