| Currently heart transplant surgery is still the most effective treatment for heart failure.However,due to the lack of heart donor,a large number of patients with heart failure die waiting for a donor.Clinicians need some kind of aided-device urgently to maintain the patient's life until they can complete heart transplant surgery.The development of ventricular assist device as such an instrument has been a hot topic in the field of biomedical engineering.Ventricular assist device which is from the beginning of the volume type blood pump to the current impeller blood pump has got considerable development.However,the blood pump developers are plagued by some problems about seal,hemolysis and blood coagulation of the blood pump.The development of computational fluid dynamics(CFD)provides ideas for solving these problems.In the specific working conditions the results of CFD simulation can provide almost all the information of internal flow field of blood pump,and developers can use the information to complete the optimization design of the structure of blood pump.In addition,it can also be combined with hemodynamics to establish the appropriate model to predict and evaluate the performance of the blood pump.The main content of this paper is to explore the impact of three different structures of ventricular assist device on blood pump performance by using CFD technology and analyze the hydraulic performance and hemolytic performance of blood pump.In order to simulate the blood flow in the blood pump,the mixture model of multiphase flow model was used in this paper,and the blood plasma and blood cell were defined as two kinds of different phases.Three different structures of the impeller were named Z,XZ and L structure.Given the same conditions Q=6.24L/min,for the pressure of 100 mmHg,the relationship of required speed of the three structures is rpm2082nrpm1950nrpm1825nLXZZ=<=<=.As can be seen,Z structure has the best ability to supply pressure.L structure is the worst.The maximum speed of three structures of Z,XZ and L is respectively 4.914m/s and 4.892m/s and 5.858m/s.By intercepting five planes vertical in the blood pump axis,and focuses on the analysis of the structure of each movement of the worst section4 and section5,we got the result that the flow of Z structure is optimal,and that XZ and L structures have suffered different degrees of secondary flow and reflux.Finally,we analysis the performance of the hemolysis of blood pump.The result showed that the maximum shear stress areas of three structures are mainly concentrated in the wall surface of the impeller and the pump outlet.Z,XZ and L these three kinds of structural area accounts for more than 150 Pa of the total surface area with respectively 0.0018%,0.0022% and 0.144%.From the simulation results,it can be known that,compared with the other two species,the Z structure has the best structure,which is mainly reflected in its high pressure for pressure capability,good flow conditions and good hemolytic performance.In addition to the flow of blood pump,there is no difference between the performance of blood pump of XZ structure and Z structure.L structure of the blood pump is the worst,which needs further improvement for these parameters,and that also shows that the simple arc streamlined blade does not have the advantage over the straight blade.Finally,the volume fraction of the second phase of the cloud shows that there are dilution and intensification in different parts when the blood flows through the blood pump. |
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