Study On The Internal Flow Field And Cavitation Characteristics Of Centrifugal Blood Pump Under Assistance Of Variable Speed

The constant rotation speed control method of ventricular assist device will reduce the pulsatility of the blood arterial pressure and cause a series of complications,causing aspiration and reflux.The variable speed auxiliary control can achieve the optimal assist state of the ventricular assist device by adjusting the speed of the blood pump,which is suitable for long-term assistance,but the rapid change of the speed can easily cause the pressure in the local position of the pump to suddenly drop,resulting in cavitation and higher hemolysis value,and hindering the rapid development of variable speed control systems.In this thesis,the self-developed centrifugal blood pump is taken as the research object.Firstly,numerical simulation is performed by CFD to analyze the pressure distribution law and cavitation flow characteristics of the centrifugal blood pump.Then,taking grade IV heart failure as an example,the MATLAB software was used to establish the parameter model of "centrifugal blood pump-left heart blood circulation system",and the speed curve of the centrifugal blood pump when it reached the best auxiliary state under grade IV heart failure,and the initial conditions at different speeds.Finally,the development law of cavitation in the auxiliary process of variable speed of centrifugal blood pump is analyzed.This study provides theoretical basis and technical support for avoiding cavitation of variable speed ventricular assist devices,and promotes the development of ventricular assist devices for clinical application.The main research contents and results are as follows:1.The steady-state numerical simulation of the centrifugal blood pump.By changing the flow and speed of the centrifugal blood pump,the steady-state characteristics of the centrifugal blood pump are analyzed from the external characteristics and internal flow field.The results show that the pressure distribution inside the centrifugal blood pump is less affected by the flow rate and more affected by the rotation speed.As the speed increases,the pressure on the impeller flow path and the surface of the impeller blades decreases sharply.The stability of the flow field in the centrifugal blood pump is proportional to the flow rate and inversely proportional to the speed.2.Measured the saturated vapor pressure of the blood,which vaporization pressure of blood at 37 ? is 45 mmHg and study the cavitation characteristics of the centrifugal blood pump.The results show that as the inlet pressure continues to decrease,the degree of cavitation gradually increases and the bubbles diffuse toward the outlet of the impeller.The cavitation in the flow channels of the impeller is asymmetrically distributed;When other conditions remain unchanged,the degree of cavitation of the centrifugal blood pump It is positively correlated with the speed of the pump;In the non-steady state,the degree of cavitation of the centrifugal blood pump increases first and then decreases and changes periodically.3.To establish the centralized parameter model of "centrifugal blood pump-left heart blood circulation system".Firstly,this thesis establishes a model of the left heart blood circulation system and verifies its accuracy;Secondly,according to the state equation of the centrifugal blood pump,the blood pump is equivalent to a centralized parameter model,which is coupled in parallel with the left heart blood circulation system model to establish the left heart blood circulation system parameter model assisted by the centrifugal blood pump;Finally,according to the speed control equation of the variable speed assist,the speed change curve of the centrifugal blood pump is obtained when it reaches the optimal assist state under the stage IV heart failure state.4.Cavitation analysis of centrifugal blood pump with variable speed assist.According to the numerical simulation results of variable speed assist to achieve the best assist state,this thesis analyzes the internal flow field and cavitation characteristics of the centrifugal blood pump under variable speed assist.The results show that the rotation speed and flow rate of the centrifugal blood pump have a great influence on the distribution of internal pressure,streamline and shear stress of the pump;During the cardiac cycle,the centrifugal blood pump only cavitation occurs during the ejection period;Cavitation not only changes the flow field and affects the working performance of the pump,but also generates larger shear stress,increasing the chance of hemolysis.