Centrifugal blood pumps are usually designed with secondary flow paths to avoid flow dead zones and reduce the risk of thrombosis. Due to the secondary flow path, the intensity of secondary flows and turbulence in centrifugal blood pumps is generally very high. Conventional design theory is no longer applicable to centrifugal blood pumps with a secondary flow path. Empirical relationships between design variables and performance metrics generally do not exist for this type of blood pump. To date, little scientific study has been published concerning optimization and experimental validation of centrifugal blood pumps with secondary flow paths. Moreover, current hemolysis models are inadequate in an accurate prediction of hemolysis in turbulence. The purpose of this study is to optimize the hydraulic and hemolytic performance of an inhouse centrifugal maglev blood pump with a secondary flow path through variation of major design variables, with a focus on bringing down intensity of turbulence and secondary flows. Starting from a baseline design, through changing design variables such as blade angles, blade thickness, and position of splitter blades. Turbulent intensities have been greatly reduced, the hydraulic and hemolytic performance of the pump model was considerably improved. Computational fluid dynamics (CFD) combined with hemolysis models were mainly used for the evaluation of pump performance. A hydraulic test was conducted to validate the CFD regarding the hydraulic performance. Collectively, these results shed light on the impact of major design variables on the performance of modern centrifugal blood pumps with a secondary flow path.

An accurate representation of the flow field in blood pumps is important for the design and optimization of blood pumps. The primary turbulence modeling methods applied to blood pumps have been the Reynolds-averaged Navier–Stokes (RANS) or URANS (unsteady RANS) method. Large eddy simulation (LES) method has been introduced to simulate blood pumps. Nonetheless, LES has not been widely used to assist in the design and optimization of blood pumps to date due to its formidable computational cost. The purpose of this study is to explore the potential of the LES technique as a fast and accurate engineering approach for the simulation of rotary blood pumps. The performance of “Light LES” (using the same time and spatial resolutions as the URANS) and LES in two rotary blood pumps was evaluated by comparing the results with the URANS and extensive experimental results. This study showed that the results of both “Light LES” and LES are superior to URANS, in terms of both performance curves and key flow features. URANS could not predict the flow separation and recirculation in diffusers for both pumps. In contrast, LES is superior to URANS in capturing these flows, performing well for both design and off-design conditions. The differences between the “Light LES” and LES results were relatively small. This study shows that with less computational cost than URANS, “Light LES” can be considered as a cost-effective engineering approach to assist in the design and optimization of rotary blood pumps.

Background Computational fluid dynamics has been widely used to assist the design and evaluation of blood pumps. Discretization errors associated with computational grid may influence the credibility of numerical simulations. Non‐conformal grid interfaces commonly exist in rotary machines, including rotary blood pumps. Should grid size across the interface differ greatly, large errors may occur. Methods This study explored the effects of non‐conformal grid interface on the prediction of the flow field and hemolysis in blood pumps using large eddy simulation (LES). Two benchmarks, a nozzle model and a centrifugal blood pump were chosen as test cases. Results This study found that non‐conformal grid interfaces with considerable change of grid sizes led to discontinuities of flow variables and brought errors to metrics such as pressure head (7%) and hemolysis (up to 14%). Conclusions The results on the full unstructured grid are more accurate with negligible changes of flow variables across the non‐conformal grid interface. A full unstructured grid should be employed for centrifugal blood pumps to minimize the influence of non‐conformal grid interfaces for LES simulations.

Inlet boundary conditions (BC) are one of the uncertainties which may influence the prediction of flow field and hemolysis in blood pumps. This study investigated the influence of inlet BC, including the length of inlet pipe, type of inlet BC (mass flow rate or experimental velocity profile) and turbulent intensity (no perturbation, 5%, 10%, 20%) on the prediction of flow field and hemolysis of a benchmark centrifugal blood pump (the FDA blood pump) and a commercial axial blood pump (Heartmate II), using large-eddy simulation. The results show that the influence of boundary conditions on integral pump performance metrics, including pressure head and hemolysis, is negligible. The influence on local flow structures, such as velocity distributions, mainly existed in the inlet. For the centrifugal FDA blood pump, the influence of type of inlet BC and inlet position on velocity distributions can also be observed at the diffuser. Overall, the effects of position of inlet and type of inlet BC need to be considered if local flow structures are the focus, while the influence of turbulent intensity is negligible and need not be accounted for during numerical simulations of blood pumps.