深海多金属结核水力集矿头流场结构数值模拟研究

深海蕴藏着丰富的多金属结核资源，受海水深度等限制，结核采集目前仍存在巨大挑战。水力式采矿具有结构简单、可靠性高的优势，是目前最具发展前景的采集方式之一。水力式采矿通过水流动力进行结核采集，喷射形成的复杂流场结构直接影响海床上结核颗粒剥离、起动、采集效率和海洋环境扰动强度，采集器离地高度、喷嘴射流角度和速度等具有较大优化空间。基于计算流体力学数值模拟研究了集矿头附近三维水流结构，分析了喷嘴射流速度和结核粒径对局部流场、床面剪切力以及结核采集能效的影响。结果表明：集矿头周围流场存在典型分区结构，包括淹没射流区、冲击区、壁面射流区、汇合区和上升区；随着喷射流速增大，最大床面剪切力近似线性增长，结核有效起动面积指数增长；随着结核粒径增大，有效起动面积减小，结核采集能效降低；综合考虑结核采集强度和采集能效，建议采集器喷射流速取8～9 m/s。

Numerical investigations on the flow structures around the hydraulic mining header of deep-sea polymetallic nodule collectors

Abundant polymetallic nodule resources are widely observed in deep seas. Owing to the large water depth and other factors, the collecting of the polymetallic nodules remains a big challenge up to now. Hydraulic mining has the advantages of simple structure and high reliability. It is one of the most promising methods at present, which collects polymetallic nodules in a hydraulic way. The complex structures of the jet flow from the nozzle have direct influence on the pickup and collection efficiency of polymetallic nodules and affect the disturbance strength to ambient marine environment. The collector-to-bed distance, nozzle jet oblique angle and flow speed have a wide range of potential optimization. Computational Fluid Dynamic (CFD) based numerical simulations were used to investigate the three-dimensional flow structures near the collector. The influences of jet flow speed and nodule diameter on the local flow field, bed shear stress and nodule collecting energy efficiency were analyzed. Simulation results show that there are typical zones in the flow field, including the zones of submerged jet, impaction, near wall jet, flow confluence and flow uprising. With the increase of jet flow speed, the maximum bed shear stress increases approximately linearly and the effective area of incipient motion of nodules grows exponentially. With the increase of the nodule diameter, both the effective area of incipient motion of nodules and the energy efficiency decrease. An optimized jet velocity ranging from 8 m/s to 9 m/s is recommended considering the combined influence on both the collecting productivity and the energy efficiency.