The low- and medium-frequency unsteadiness manifesting when a low-speed turbulent boundary layer separates from a solid surface and reattaches again further downstream have been extensively reported in the literature. Such unsteadiness is known to be detrimental to a variety of industrial flows through the generation of noise, vibration, or unsteady loads. Although the existence of both the low-frequency breathing and the medium-frequency shedding mode appears to be widely established in the literature, the exact mechanism of their appearance remains unclear. This particularly applies to the low-frequency breathing mode, which has so far only been detected in experimental investigations.
In the TSBdyn project we apply classic and novel stability analysis tools to analyze both the breathing and shedding characteristics of various flows featuring a pressure-induced TSB with the particular aim of clarifying whether the low-frequency breathing mode is driven by an absolute instability in the flow and whether the medium-frequency shedding mode occurs due to convective instability. In order to perform the stability analyses, experimental (e.g. PIV, HWA) or numerical databases (e.g. DNS, LES) serve as the base flow whereas the characteristic frequencies as well as the amplification of the dynamic phenomena under consideration are extracted from experimental data (e.g. unsteady wall-pressure measurements).