血泵是一种能够部分或全部替代人体心脏泵机能的机械辅助循环装置，对提高心衰等心血管疾病的治疗水平、降低心血管病人的死亡率、提高治愈率和改善病人的生活质量等起着重要作用。国内外众多的研究者已经对离心式血泵进行了大量的研究，而对更适合人体应用的轴流式血泵研究并不多。 本文设计了一种新型的轴流式磁悬浮血泵，其转子由泵机一体化的直流无刷电机驱动，且只使用两个圆锥型磁悬浮轴承即可实现转子在五个自由度上的稳定悬浮，简化了泵内结构，缩小了血泵体积，提高了其生物相容性。独特的螺旋型叶片置于圆柱型转子的内部，使转子的质量分布于转子的外缘，增加了转动惯量，从结构上利于实现转子的稳定悬浮，同时易于布置电机和磁轴承。泵壳与转子之间的环形狭缝内存在冲刷流动，以减少此处由于流动停滞生成血栓的几率。 利用FLUENT软件对磁悬浮血泵内的流动进行了数值模拟，模拟时把血液看作是动力粘度和密度分别为3.6×10⁻³Pa·s和1.055×10³kg·m⁻³的牛顿流体。模拟结果表明该轴流血泵在转速12000 rpm、流量5 L·min⁻¹时扬程为1.32×10⁴Pa,可满足人体血液循环的需求。计算了血泵内的流场分布，发现由于叶轮的高速旋转，叶轮后出现了类似于卡门涡街的旋涡，造成流动不稳定。通过加装四片弧形出口导叶的方法对血泵结构进行了优化，改善了流场。 本文介绍了切应力导致溶血和凝血现象的发生机理，发展了通过数值手段定量计算血液破坏的方法。根据数值模拟的结果，利用拉格朗日方法追踪由血泵入口截面上均匀分布的540个流体质点所形成的540条迹线，结合FLUENT的离散相模型和UDF功能，求解了血泵的溶血指标和凝血指标，结果与已有文献的数值相当，显示出雷诺切应力是造成血液破坏的主要原因。 血液是非牛顿流体，但迄今国内外在旋转式血泵的研发和设计中都把血液当作牛顿流体来处理，而关于旋转式血泵内非牛顿流体流动特性的报道甚少。本文选用黄原胶水溶液作为血液模拟流体，在放大1.5倍的模型内进行了上述轴流式血泵的水力性能和内部流场的测量，模型血泵使用滚珠轴承且由普通高速电机驱动。通过测量不同温度、不同浓度下黄原胶水溶液的流变特性，发现黄原胶水溶液与血液一样，都是典型的剪切稀化流体，其中20℃时0.04%浓度或37℃时0.06%浓度的黄原胶溶液与血液流变特性接近。 分别以20℃的黄原胶水溶液和水为工质，得到了模型血泵在4300-6500 rpm转速范围内的水力特性，其中黄原胶溶液的重量百分比浓度分别为0.04%、0.06%和0.1%，实验过程中温度偏差控制在±0.1℃。测量表明，虽然黄原胶溶液的粘性远高于水，然而在本文实验参数范围内，相同流量和转速下，以黄原胶溶液为工质时的扬程却高于水时的扬程，最大相差20%左右。黄原胶水溶液具有弱弹性，本课题组发现在湍流状态下黄原胶水溶液呈现明显的减阻效应，相关文献也有类似报道。据此推测在高转速条件下血泵内也存在减阻效应，导致粘性耗散相应减少，扬程与水时相比有所增加。本文关于高转速时血泵内非牛顿流体扬程高于牛顿流体在相同工况下相应扬程的发现尚属首次。非牛顿流体不遵守牛顿流体的相似律，但当泵雷诺数高于极限雷诺数时，在无量纲扬程-无量纲流量图中同一浓度的非牛顿流体的数据点也会落到同一条曲线上，称此曲线为非牛顿流体相似曲线。非牛顿流体相似曲线与牛顿流体相似曲线不相重合。 特别研究了对血泵水力性能和生物相容性影响较大的转子与泵壳之间狭缝内的流动细节。测量了泵壳内壁面的压强分布，利用TSI-1268W型热膜探头测量了壁面切应力分布，利用LDV测量了狭缝中部沿轴向的速度分布。结果表明，狭缝内流体的高速旋转运动导致狭缝内压强和壁面切应力均处于较高的水平；狭缝内确实存在轴向冲刷流动，且其流动方向与主流相反。 对模型血泵内水做工质时的流动进行了数值模拟，计算与实验测量结果基本吻合。 ①本研究得到国家自然科学基金(编号：50576074)资助。 关键词：轴流磁悬浮血泵；实验测量；非牛顿流体；黄原胶水溶液；水力特性 论文类型：应用基础

 Being a mechanical assistant device, blood pump can entirely or partly replace the pump-performance of natural heart. It plays an important role in treatment of cardiovascular disease and can significantly improve survival rate and the quality of life of patients with severe congestive heart failure. Centrifugal blood pumps have been studied extensively, however, axial blood pumps, which are more suitable for application in human body, received less attention. A new design of axial blood pump is presented in this study. The rotor of the pump is driven by an integrated brushless DC motor and suspended by only two conical magnetic bearings, which simplifies the inner structure, reduces the size and increases the biocompatibility of the blood pump. The spiral impeller is embedded in the center of rotor, which provides rather large moment of inertia to increase the rotating stability of the suspended rotor and make it easy to arrange the motor and bearings. A washout flow is expected to be formed in the clearance between the rotor and the pump shell, reducing the probability of thrombus formation. The commercial code FLUENT is used to simulate the inner flow of the axial blood pump with blood treated as a Newtonian fluid with viscosity of 3.6×10⁻³ Pa·s and density of 1.055× 10³ ㎏·m⁻³. The simulation indicates that the blood pump can develop a head of 1.32 × 10⁴ Pa at the rotating speed of 12000 rpm and flow volume of 5 L·min⁻¹, which meets the needs of blood circulation in human body. The flow fields in the blood pump show that a series of vortexes just like Karman vortex street occur downstream the impeller, making the flow unsteady. To improve the flow fields, 4 arc guide vanes are added downstream of the rotor, and re-calculaton shows the vanes can effectively eliminate the vortexes. The mechanism of hemolysis and thrombus caused by shear stress are analyzed, and the numerical method to evaluate the blood damage is developed. Based on the simulated results, a Lagrange method is employed to trace the 540 path lines formed by 540 fluid particles which evenly scattered at the pump inlet plane at the starting moment. The hemolysis index and platelet lysis index of the pump are then calculated using the Discrete Phase Model and User Defined Function of FLUENT. The magnitudes of the two indexes are equivalent to the values from other researchers. Human blood, which is a non-Newtonian fluid, has been treated as a Newtonian fluid in the process of R & D or rotary propeller blood pump, and hydrodynamics of Non-Newtonian fluid in rotary pumps are rarely reported. In the present study, Non-Newtonian fluid hydrodynamics in a 1.5:1 model pump driven by a high speed motor are studied using aqueous Xanthan gum solutions as the analog fluid for blood. The rheological properties of aqueous Xanthan gum solutions at different concentration and temperature are measured. It is found that Xanthan gum solution, just as blood, is a shear thinning fluid, and the apparent viscosities of 0.04% solution under 20℃ and of 0.06% solution under 37℃ are well matched with that of blood. Non-Newtonian fluid hydrodynamics in the pump model are studied using water and aqueous Xanthan gum solutions with concentrations of 0.04%, 0.06% and 0.1 %, respectively, as working fluids, while the fluid temperature is maintained around 20±0.1℃ during the entire course of measurements. Measurements indicate that in the range of present experimental parameters the head for Xanthan gum solution is always higher than that for water at same flow volume and same rotating speed with a maximum difference of 20%, although the solutions have much higher viscosities. This unexpected phenomenon may be attributed to the drag-reduction effect of Xanthan gum solution. Our group found that addition of Xanthan gum powder into turbulent water flow in a tube leads a profound reduction of friction loss, and there are also similar reports in the literatures. It is rational to suppose that the drag-reduction would take effect in the model pump when the rotating speed of the pump is high enough, so that viscous dissipation in it is reduced and the head is subsequently raised above that of water at the same conditions. In the dimensionless head vs. flow volume diagram, aqueous Xanthan gum solutions do not comply with the similarity law of Newtonian fluids, data points of Xanthan gum solutions will collapse on a single curve when the pump Reynolds number of the solution exceeds a critical value, and the curve is referred to as similarity curve of Non-Newtonian fluid. The Non-Newtonian similarity curve is above the Newtonian similarity curve in the diagram at the parameter range of present study. Special attention is paid on the flow details in the clearance between pump shell and rotor, which have a significant effect on the hydrodynamics and biocompatibility of the pump. The wall pressure, wall shear stress and the velocity at the middle of the clearance are measured using 1151 differential pressure transducer, TSI-1268W hot film sensor and LDV, respectively. Measurements indicate that both wall pressure and wall shear stress are rather high, which is obviously induced by the high rotating speed of the pump, and the axial washout flow does exist in the clearance with a direction opposite to that of main flow. Numerical simulation is also carried out for the hydrodynamics of water in the model pump, and the computation agrees reasonably with measurement. This study is supported by the National Science Fundation of China (Grant No.: 50576074). KEY WORDS: Magnetically suspended axial blood pump; Numerical simulation; Non-Newtonian fluid; Aqueous Xanthan gum solution; Hydrodynamics TYPE OF DISSERTATION: Applied Fundamentals