Modal analysis of aerospace and geophysical boundary layers.

A linear stability code was written and used to calculate the stability of surface and bottom Ekman layers. Then, the stability of a water column containing both a surface and bottom Ekman layer was calculated to investigate possible mode interactions. Mode interaction was observed when the unstable vortices from the surface and bottom layers were aligned and the ocean depth was sufficiently small. This mode interaction could be a factor in the creation of Langmuir supercells in shallow coastal regions. Additionally, three modal decomposition techniques – proper orthogonal decomposition (POD), smooth orthogonal decomposition (SOD) and dynamic mode decomposition (DMD) – were applied to a sample data set composed of Tollmien-Schlicting (TS) waves over a flat plate, which were calculated with the aforementioned linear stability code. The SOD was able to pair mode shapes with specific frequencies, suggesting that it could be a useful tool for revealing underlying disturbances in boundary layer experiments.