磁流变液壁面滑移发生机理及影响因素研究

Wall slip phenomenon is a significant problem in determination of the rheological parameters and practical application of magnetorheological fluids (MRF), and has drawn considerable attention in the past few years. The investigation of this project into wall slip phenomenon of MRF includes the following three facets : (1) investigating the aggregates of particles in the MRF and the interaction between particles and wall plates in order to reveal the mechanism of wall slip. It is worth emphasizing that the influence between the aggregates of particles and the distribution of magnetic field is an interactive process. Researching on the effect of material, morphology, roughness of wall surface to the interaction between particles and wall by particle-based microscopic analyzing approach. (2) Modelling the shear flow and differential pressure flow based on the MRF constitutive models in conjunction with the Navier wall slip boundary conditions so as to evaluate the impact of wall slip and reveal the nature of its apparent behaviors. (3) Performing experiments to observe and analyze the apparent behaviors of wall slip of MRF which is in the work mode of shearing and flowing respectively; combining the conclusions of theoretical analysis, numerical simulations and experiments to obtain the inherent laws that wall slip is influenced by some factors, such as wall conditions, interior pressure in the channel and so on. This project will promote the measurement of the rheological parameters as well as the practical application of MRF.

壁面滑移现象是磁流变液（MRF）的流变特性测试及其应用中一个非常显著的问题，近年来引起了国内外学者的热切关注。本项目针对壁面滑移现象从三个方面展开研究：（1）通过建立MRF中铁磁颗粒的动力学模型，研究铁磁颗粒在与磁场的耦合作用下发生链化聚集以及与壁面的相互作用，揭示壁面滑移现象的发生机理。从颗粒级的微观角度揭示壁面的材料、形态、粗糙度等因素对铁磁颗粒与壁面相互作用的影响。（2）基于MRF本构模型和Navier滑移模型建立MRF在不同壁面滑移边界条件下的剪切流模型和压差流模型，评估壁面滑移对力学模型的影响，从理论上揭示壁面滑移表观现象的实质。（3）设计实验观测和分析MRF在剪切模式和流动模式下发生壁面滑移的表观现象，结合理论分析、数值模拟和实验测试的结论，揭示壁面滑移受壁面条件及内部压强等因素影响的内在规律。本项目对磁流变液的流变性能测试和实际应用有重要意义。

磁流变液是一种非常有应用前景的智能材料，然而由于壁面滑移的存在及其发生机理和影响规律尚不明晰，对磁流变液性能测试与应用造成不利影响。本项目针对磁流变液壁面滑移的研究内容及结论如下 ：.1，磁流变液在壁面滑移边界条件下的力学建模及内在规律研究。（a）理论及试验分析表明，宜采用Navier应力滑移边界条件描述磁流变液的壁面滑移现象。剪切模式下，滑移系数在剪切率较低时的量级为10-3，随着剪切率的增大，壁面滑移现象逐渐减弱，剪切率在350s-1左右基本消失。（b）基于Navier应力滑移边界条件建立的压差流模型表明，磁流变液屈服强度越高，缝隙高度越小，壁面滑移导致压力梯度下降的幅度越明显；阻尼通道中可能发生磁流变液未屈服而整体摩擦滑移；壁面滑移受磁流变液粘度的影响非常小。.2，磁流变液流变性能测试及摩擦磨损试验研究。（a）建立了压差流动模式下的测试理论依据，设计了剪切率可达3.0×105 s-1的测试装置。试验表明，壁面粗糙度和壁面材料对测试结果几乎没有影响，缝隙高度和缝隙长度对测试结果有影响。（b）基于非导磁材料转子的剪切模式测试试验表明，光滑壁面转子测试的应力曲线在低剪切率阶段存在明显的壁面滑移；壁面粗糙度对零场粘度测试没有影响。（c）摩擦磨损试验表明，磁流变液对器件磨损的影响因素中，载液粘度>铁颗粒粒径>铁粉质量分数。 .3，磁流变液铁磁颗粒与壁面相互作用的微观机理研究。拟采用颗粒动力学与磁场耦合仿真，为壁面滑移提供颗粒级的微观解释和分析能力，但由于计算量大未能实现。结合实验以及对已有文献的总结，得到结论：壁面材料和壁面形貌（结构）影响磁流变液在壁面处 “锚栓”的形成，进而影响壁面滑移；壁面为导磁材料时，壁面粗糙度对磁流变液的应力发挥影响不大；壁面为非导磁材料时，粗糙的壁面或沟槽有利于磁流变液屈服应力的发挥。.本项目可为磁流变液流变性能的测试及其应用提供理论指导和科学依据。