Our paper “Standing-wave dynamics in low-frequency breathing of a turbulent separation bubble” was recently published in the Journal of Fluid mechanics https://doi.org/10.1017/jfm.2026.11191.
Turbulent separation bubbles are recirculation regions that form when a turbulent boundary layer separates from a surface and reattaches downstream. They can drive vibrations, noise, fatigue, and thermal load fluctuations in many engineering applications. Despite decades of research, their very low-frequency “breathing” motion still poses open questions.
Our study examines this low-frequency “breathing” motion over a backward-facing ramp using time-resolved PIV data, resolvent-based modelling and modal analysis. We show that spanwise sidewall confinement induces standing-wave patterns through wall reflections, and that these dynamics can be captured by a resolvent-based standing-wave model.
Global stability analysis identifies a zero-frequency eigenmode consistent with a centrifugal mechanism driving the breathing motion, with further downstream amplification via non-modal lift-up.
These results have implications on the routine use of spanwise-periodic boundary conditions in simulations, and provide a low-order framework for predicting sidewall-induced modal dynamics in pressure-driven separated flows.
This work was made possible by FELiCS! The resolvent computations and global stability analyses at the core of this study were handled efficiently and flexibly by our framework, effortlessly managing a massive computational workload. Building on this momentum, we will soon push FELiCS to perform large tri-global analyses. Stay tuned for more updates!
