Current researches show that the constant speed mode adopted by the existing commercial blood pump may cause damage to the body. The way to solve this problem is to produce pulsating flow by changing the speed of the blood pump’s impeller. But at present, the flow field of the blood pump is not clear, when it changes speed, and the coupling between blood pump and body has not been considered in the simulation of the flow field. A multiscale coupling model combining hemodynamics (0D) and Computational Fluid Dynamics (3D) was established in this paper to solve the problem, and a speed change curve consistent with the ventricular motion was selected. The hemodynamics, shear stress, and hemolysis changes of 6000 rpm at different amplitude (2000, 3000, and 4000 rpm) were simulated, analyzed, and compared with the constant speed (7000 rpm). The results show that the pressure difference obtained by simulation is consistent with the experimental results, and the flow generated by the natural heart still flows through the blood pump, thus changing the working point of the blood pump. When the blood pump works at the changing speed, it could produce more pulsation, and the shear stress and hemolysis in the blood pump increase with the rising of speed and flow. But according to the hemolysis score of a single cardiac cycle, the hemolysis value of the changing speed model at an amplitude of 4000 rpm is only 11.71% higher than that of constant speed at 7000 rpm.
Computational fluid dynamics is an essential tool for the flow field analysis of the blood pump. The interface processing method between the dynamic/static regions will affect the accuracy of simulation results, but its influence on the simulation results is still unclear. In this study, the axial-flow blood pump was taken as the research object, and the effects of the mixing plane, frozen rotor, and sliding mesh methods on the following results were compared: flux conservation at the interface, hydraulic characteristics, and velocity field distribution. In parallel, the particle image velocimetry experiment was carried out to measure the velocity field of the impeller, the inlet, and the outlet area of the blood pump. The results show that the above methods have significant differences in flux conservation between the impeller and the back vane. The average surface energy flux’s error of frozen rotor and sliding mesh are 0.7% and 0.72%, respectively, while the mixing plane method reaches 3.6%. This nonconservative transfer affects the distribution of the downstream velocity field, and the velocity field predicted by the mixing plane at the outlet is quite different. It is suggested to use the frozen rotor method and the sliding mesh method in the simulation of the blood pump.
The blood pump is an implantable device with strict performance requirements. Any effective structural improvement will help to improve the treatment of patients. However, the research of blood pump structure improvement is a complex optimization problem with multiple parameters and objectives. This study takes the splitter blade as the object of structural improvement. Computational fluid mechanics and neural networks are combined in research and optimization. And hydraulic experiments and micro particle image velocimetry technology were used. In the optimization study, the number of blades, axial length and circumferential offset are optimization parameters, and hydraulic performance and hemolytic prediction index are optimization targets. The study analyzes the influence of each parameter on performance and completes the optimization of the parameters. In the results, the optimal parameters of number of blades, axial length ratio, and circumferential offset are 2.6° and 0.41°, respectively. Under optimized parameters, hydraulic performance can be significantly improved. And the results of hemolysis prediction and micro particle image velocimetry experiments reflect that there is no increase in the risk of hemolytic damage. The results of this study provide a method and ideas for improving the structure of the axial spiral blade blood pump. The established optimization method can be effectively applied to the design and research of axial spiral blade blood pumps with complex, high precision, and multiple parameters and targets.
The blood pump is a medical device used to assist or replace the diseased heart. Research on the structure of blood pumps has been committed to achieving better hemolysis and hydraulic performance. The purpose of this study was to find some effective ways to improve design methods and hydraulic structures. The research contents of improvement include: (1) improved blade streamline design method; (2) conical impeller hub; (3) additional auxiliary blades. Characteristic analysis and parameter design were carried out on the above three aspects. The methods used in this study included Dynamics (CFD) simulation, hydraulic experiments, and Particle Image Velocimetry (PIV) experiments. The results showed that this improved streamline design method could improve the distortion of blades and ensure a smaller impeller length. And, in the enhanced design of the hub, it is designed to be conical with inlet and outlet diameters of 7.5 and 12.8 mm, respectively. Furthermore, the auxiliary blades between the main blades are analyzed and designed. The results have the best performance optimization effect when the length of the auxiliary blades is 55% of the main blades. In general, the structural improvements in this study achieved the effect of improving hydraulic performance and avoiding increased hemolysis. These methods can be considered as an effective means of improving blood pump performance.
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