Study on the Mechanism and Control Measures of Sediment Deposition in the Forebay of a Forward Pumping Station

To address the problems of disordered flow patterns, wall-separated recirculation, and sediment deposition that commonly occur in the forebay of forward-facing pumping stations on sediment-laden rivers, the first-stage Xin Zhuangji Pumping Station in Ningxia was selected as the study case. A three-dimensional numerical simulation was conducted using the Realizable k-ε turbulence model coupled with the Mixture two-phase flow model for water–sediment flow. The regulation effects of splayed guide walls with different guide-wall deflection angles on the velocity distribution, vortex structures, and sediment deposition in the forebay were investigated. The results show that large-scale recirculation zones exist on both sides of the prototype forebay, accompanied by uneven velocity distribution and severe sediment deposition within the recirculation regions. The installation of splayed guide walls can effectively suppress lateral recirculation, expand the mainstream flow region, and reduce the deposition area. However, the regulation effect of the diffusion-type guide wall varied significantly with the guide-wall deflection angle. Since the main objective of this study was to control sediment deposition rather than to maximize a single hydraulic indicator, a multi-criteria screening method oriented toward sediment-reduction control was adopted. Under the (θ = 25°) scheme, the reduction ratio of the overall potential deposition area based on the primary threshold criterion reached the maximum value of 53.67%, the recirculation area on plane Z1 decreased by 23.23%, the global recirculation coefficient increased to 68.69%, and the sediment deposition efficiency decreased to 0.033. The axial velocity uniformities at the suction-pipe sections of pumps B# and C# were 71.23% and 80.61%, respectively. Although the (θ = 30°) scheme produced the highest velocity uniformity for pump B# and showed a slightly better reduction effect on local high-concentration sediment-enrichment regions, the (θ = 25°) scheme exhibited a more balanced improvement in overall sediment-deposition control and flow-pattern regulation. Therefore, under the investigated operating condition, the (θ = 25°) scheme is recommended as the guide-wall deflection angle oriented toward sediment-reduction control.