Investigation On Simulation Strategies For Flow Characteristics And Hemolysis In Blood Contacting Devices

Cardiovascular diseases have become the main cause of death,and the incident rate has also increased year by year,which seriously threatens human health.Artificial cardiovascular devices have become an important means of treating patients.In blood contacting devices such as ventricular assist devices,the flow field will produce very high non-physiological shear stress,and the resulting hemolysis has been a hot topic.The U.S.Food and Drug Administration(FDA)has published two benchmark models: nozzle and standard centrifugal blood pump models for evaluation purposes.This study investigated the flow characteristics and hemolysis simulation strategies for blood contacting devices.The project used the Computational Fluid Dynamics(CFD)to study the flow field and hemolysis in the nozzle models with different sizes as well as in the blood pump benchmark model.The simulation results were verified with experimental data.Typical hemolysis prediction model,in which hemolysis is related to the effective shear stress and exposure time,and energy-dissipation-based hemolysis estimation model were compared in this study.The work of the thesis was divided into the following parts:(1)Research on turbulence model,typical hemolysis prediction model and energy-dissipation-based hemolysis estimation model.(2)Numerical analysis of the FDA nozzle benchmark model and its variation in geometry using the method of Large Eddy Simulation(LES)and WALE model to simulate the flow field under two different conditions.(3)Hydraulic performance experiments of the nozzle model using a customized experimental platform.(4)Numerical analysis of the FDA blood pump benchmark model.The Reynolds Averaged Navier-Stokes(RANS)method with RNG model was used to explore the effects of the rounding and different meshing methods(structural or unstructural grids)on the flow field and hemolysis prediction under three pump operating conditions.(5)The FDA benchmark blood pump was simulated using the typical hemolysis prediction model and the energy-dissipation-based hemolysis estimation model.The results were compared and evaluated.The results showed that the velocity and pressure of the nozzle model changed greatly when the diameter suddenly changed.It was consistent with the published results.Compared with experimental results,the data of numerical analysis was reliable.It was found that the rounding and the meshing method of blade had considerable impacts on pump head,flow field and predicted hemolysis levels.And the results of energy-dissipation-based hemolysis estimation model were closer to FDA publications.Furthermore,there were certain correlations between the details of the flow field and pressure head,but pressure head was not very sensitive to the characteristics of flow field.The study was of great importance for better use of CFD to aid the hemocompatibility design.