Flow Patterns of Sudden Expansion Flow and Geometric Boundary Effects in the Changsha Junction’s Multiline Ship Locks

The rapid economic growth has driven the transformation of ship locks into multiline configurations. However, the unsteady expansion flow generated by discharge in multiline ship locks poses a threat to the navigation safety of vessels in the shared approach channel. In this paper, a TK2D two-dimensional hydrodynamic model is used to analyze the response patterns of water depth and dike structures to the movement of unsteady sudden expansion flows. The results reveal that unsteady sudden expansion flows manifest with a prominent initial wave amplitude that progressively diminishes, expanding in a fanlike pattern and gradually undergoing separation. Enhancing the water depth within the approach channel can mitigate the lateral velocity but amplify the distortion of the main flow postexpansion, culminating in a more chaotic flow pattern. However, the sloped dike structure demonstrates effective guidance, and submerged sloped dike has good retention effect on expansion flows, with the peak lateral flow velocity reducing as the slope ratio decreases. The synergistic strategies of augmenting water depth and incorporating flow-diverting structures can further attenuate the diffusion intensity of sudden expansions.