Asymmetric evolution of vortex-tube structures in side-by-side ventilated twin cavities at a fixed low Froude number

This study experimentally investigates the closure-region interfacial morphology and vortex-tube evolution of side-by-side ventilated twin cavities at a fixed low Froude number. Time-resolved cavity images are acquired using high-speed imaging under different lateral spacing ratios L_H /D_C and ventilation coefficients C_Q. Proper orthogonal decomposition, information entropy, and K-medoids clustering are combined to quantify vortex-tube disorder and identify coarse-grained evolution states. The results show that twin-cavity coupling produces a spacing-controlled asymmetric evolution pattern. As L_H /D_C decreases, gap-passage acceleration strengthens the deflection of the local gas–liquid trajectory toward the gap side, increases the induced strain and co-flow shear acting on the gap-side vortex tubes, and promotes their transition from continuous low-disorder structures to undulating, broken and fragmented high-disorder states. By contrast, the outboard-side vortex tubes are more likely to retain continuous low-disorder states. Within the tested range, changes in L_H /D_C primarily redistribute the side-dependent vortex-tube states, whereas changes in C_Q mainly modify the relative scale of the vortex tubes. These results support a physically based link between geometric coupling, gap-passage acceleration, and disorder-state evolution in ventilated twin-cavity wakes.