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Stochastic reduced-order model for the bimodal low-frequency dynamics of a turbulent separation bubble
Phys. Rev. Fluids 11, 064603 – Published 1 June, 2026
DOI: https://doi.org/10.1103/xt43-7x48
Abstract
The low-frequency unsteadiness of turbulent separation bubbles is manifested in a contraction and expansion of the reverse-flow region. This study shows that, in a pressure-gradient-induced turbulent separation bubble developing in a half-diffuser, the dominant long-time behavior follows nonlinear stochastic dynamics. Planar time-resolved particle image velocimetry reveals a spanwise-organized coherent structure with anticorrelated core and sidewall regions. Its temporal evolution is quantitatively described using a Langevin equation, modeling both the deterministic drift and stochastic forcing of the dynamical system. This model suggests that the low-frequency unsteadiness may arise from stochastic forcing, resulting in transitions between two equilibrium states. The methodology and findings documented in the present paper therefore constitute a significant step toward understanding turbulent separation bubbles as probabilistic dynamical systems.
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