Flow dynamics of ventilated bubbles and inclined bubble chains near a plate leading-edge under separated flow

Controlling near-wall ventilation-rising dynamics and achieving steady-state bubble chains are central to modulating the hydrodynamic performance of structures in cross-flow. Unlike the case in static water or fully developed turbulent boundary layers, ventilation-rising dynamics under the influence of flow boundaries such as separated flows are more complex, and the steady-state characteristics of bubble chains are less pronounced. To address this ventilation evolution mechanism and the flow field induced by bubble chains, a leading-edge separated flow was constructed using a water flume and a square-head flat plate. The outflow stability of bubbles at the orifice was evaluated based on bubble morphology, size, and detachment characteristics. The dynamic behavior of bubble expansion and rising, together with the disturbed flow field at the separation leading edge, was captured under various incoming flow velocities and ventilation flow rates. The increase in flow randomness and its time-averaged characterization were compared using instantaneous and time-averaged induced flow fields as the two-phase parameters varied. The results show that, depending on the two-phase flow intensity, the near-orifice bubble expansion at the separation leading edge can be divided into three behaviors: two-phase coupling, ventilation resistance deflection, and inflow acceleration deflection, which produce differentiated disturbances in the near-wall separation bubble. The cross-flow shear/drag governs bubble detachment ( τ ∼ Re δ 1.08 We Q 0.04 ) and bubble chain deflection ( θ ∝ Fr d 0.372 U * −0.092 ) at higher flow velocity, modulating the ventilation inertia. As the two-phase flow intensifies, stable bubble outflow is weakened by the random diffusion and interaction of near-wall vortices, and turbulent fluctuations on the backflow side of the bubble chain increase, changing the dominant mechanism of near-wall reattachment-recovery flow field.