Ashraf, Intesaaf; Tiwari, Neetu; Dorbolo, Stephane; (2025) Wake dynamics of a square cylinder while moving upward in quiescent water. Physics of Fluids , 37 (12) , Article 122132. 10.1063/5.0297356.

Text Wake dynamics of a square cylinder while moving upward in quiescent water.pdf - Accepted Version Access restricted to UCL open access staff until 2 December 2026. Download (45MB)

Abstract

We experimentally investigate the wake dynamics of a square cylinder rising through quiescent water over a range of Froude numbers (Fr). Time-resolved particle image velocimetry provides velocity and vorticity fields that enable pressure reconstruction and vortex characterization. Diagnostics based on swirl strength (λ<inf>ci</inf>), the Okubo–Weiss parameter (W), and a shear–vortex interaction measure (Λ) reveal that the wake is governed by a persistent pair of counter-rotating vortices rather than by periodic shedding. Circulation exhibits a two-regime dependence on Fr, with a sharp increase below Fr ≈ 1 and saturation above this threshold, mirroring entrainment force scaling reported previously. While vortex area remains nearly constant, swirl strength and negative-W regions expand with Fr, indicating that entrainment enhancement arises from intensified rotation rather than an enlarged vortex footprint. These findings provide new physical insight into vortex-free-surface interactions and enrich the understanding of entrainment mechanisms in unsteady wakes, with implications for multiphase flows and the hydrodynamic design of naval and offshore structures.

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