非均匀高分子聚合物用于水中航行器外部流动减阻特性研究

A small amount of polymer additives with high molecular weight may dramatically reduce the friction drag in turbulent flow. This technology was applied to reduce the fuel consumption for transporting crude oil successfully. Furthermore, the technology has the potential to reduce the drag for the external flow such as the drag of ship and the drag of underwater vehicle. However, the polymer solution for those external flows isn’t homogeneous as its counterpart of inner flows. In this project, we would like to study the inhomogeneous viscoelastic flow outside of the underwater object by numerical simulation. Considering the turbulent flow can be modified considerably, on one hand the dispersion of polymer molecular should be taken into account in turbulent flows; on the other hand, it is necessary to study the polymer’s influence on the flow modification. In this project, we would like to study the friction drag of an object under the influence of inhomogeneous polymer solutions couple with these two factors together. Based on our previous in-house computational fluid dynamics code which can simulate a flow with homogeneous polymer additives, we will model the dispersion of polymer molecular in turbulent flow to study the interaction between the Newtonian flow and high molecular weight polymer. The maximum drag reduction and small scale fluctuation are going to be focused in this project while the inhomogeneous polymer solution stay in a state of statistical equilibrium. Furthermore, the concentration of polymer additives and the friction drag on a zero-pressure-gradient boundary layer with polymer injection will be studied in this project. The numerical results will be adequately validated by experimental results; the influence of polymer on drag and flows in the boundary layer will be studied by experiments by means of Anti-Fouling marine paint contains polymer. The current investigation can be served as an effective theoretical support and an executable method for the drag reduction with an external flow such as a ship as well as an underwater vehicle with polymer additives on the surface.

水中加入微量的水溶性高分子聚合物可大幅降低湍流引起的摩擦阻力。对于诸如船舶与水中兵器等涉及外部流动的阻力，该技术具有巨大的减阻潜力。然而对于外部流动而言，物体表面的高分子聚合物并非均匀分布。本项目拟采用数值模拟的方法，研究水中物体外部的非均质聚合物作用下的粘弹性流场。鉴于高分子聚合物可大幅更改湍流结构，本课题一方面需考虑流动对聚合物的湍流扩散作用，另一方面需要考虑非均匀的聚合物对流动的更改；耦合两方面来探索非均质聚合物对物体表面摩擦阻力的影响。拟在前期工作基础上，考虑聚合物分子受对流与扩散作用，通过计算分析在聚合物浓度梯度达到统计平衡态时的减阻能力以及小尺度脉动规律，并进一步研究有聚合物扩散的非定常零压梯度边界层的阻力与聚合物浓度扩散行为。此外将通过实验对数值计算进行验证，并通过实验方法研究含聚合物自抛光防污涂料对阻力及边界层流动的影响，为外部流动的聚合物减阻提供可行的实施方案与理论指导。

少量的水溶性高分子聚合物添加可以更改湍流行为，从而大幅获得减阻的效果。以往的研究主要侧重于聚合物溶液对内部流动的影响。本项目则以水下航行器的聚合物减阻为背景，开展外部流动的减阻规律研究。在本项目的开展过程中，主要研究了聚合物溶液作用圆柱、水翼、小球及细长体等外部绕流。研究中以减阻为主线，重点考察了边界层附近流动行为，尾流特性在不同的聚合物浓度或者粘弹性流体的聚合物粘性比，维森伯格数与雷诺数的影响。在几种外部流动的研究中，无论是数值模拟还是实验研究，相比牛顿流体均同时发现了减阻与阻力增加的情况。对于圆柱绕流的最大减阻量可高达50%，同时在存在瞬态升力的漩涡脱落机理中，发现漩涡脱落的频率和强度都受到了聚合物的影响，聚合物倾向于抑制升力幅值与漩涡脱落。数值与实验的结果证实了水溶性高分子聚合物可以用于水下航行器减阻，但在使用这一技术时，需要更进一步的额外关注新引入的问题：控制水下航行器机动特性的机翼所提供的升力可能会同时也大幅降低。