Secondary stability analysis of crossflow vortices using BiGlobal theory on PIV base flows

A combined experimental and numerical approach to the stability analysis of swept-wing boundary layers is presented. Secondary instabilities to the primary crossnow vortices in a swept-wing boundary layer are resolved by applying BiGlobal stability theory to the mean flow field measured with tomographic PIV, solving for the high-frequency type I mode. Stability results converge with respect to the mean flow ensemble size and are independent of the treatment of the handling of the exterior of the measurement domain. The recovered BiGlobal mode agrees with the instantaneous tomographic PIV and hot-wire anemometry data. This is the first occasion where this approach using a measured base flow for stability analysis is applied to this application case, directly avoiding modelling the primary vortices’ receptivity. Using the developed framework, further insight can be gained on the linear growth and later stages of transition via the primary and secondary crossflow instabilities.