Influence of rotor impeller structure on performance improvement of suspended axial flow blood pumps

BACKGROUND

The hydrodynamic suspension structure design of the axial blood pump impeller can avoid the problems associated with using mechanical bearings. However, the particular impeller structure will impact the hydraulic performance and hemolysis of the blood pump.

METHOD

This article combines computational fluid dynamics (CFD) with the Lagrange particle tracking method, aiming to improve the blood pump's hydraulic and hemolysis performance. It analyzes the flow characteristics and hemolysis performance inside the pump. It optimizes the taper of the impeller hub, the number of blades, and the inclination angle of the circumferential groove at the top of the blade.

RESULTS

Under certain rotational speed conditions, an increase in the taper of the impeller hub or the number of blades can increase the pumping pressure of a blood pump, but an increase in the number of blades will reduce the flow rate. The design of circumferential grooves at the top of the blade can increase the pumping pressure to a certain extent, with little impact on the hemolysis performance. The impeller structure is optimized based on the estimated hemolysis of each impeller model blood pump. It could be seen that when the pump blood pressure and flow rate were reached, the optimized impeller speed was reduced by 11.4%, and the estimated hemolysis value was reduced by 10.5%.

CONCLUSION

In this paper, the rotor impeller structure of the blood pump was optimized to improve the hydraulic and hemolytic performance effectively, which can provide a reference for the related research of the axial flow blood pump using hydraulic suspension.

Enhanced discrete phase model for multiphase flow simulation of blood flow with high shear stress

Shear stress is often present in the blood flow within blood-contacting devices, which is the leading cause of hemolysis. However, the simulation method for blood flow with shear stress is still not perfect, especially the multiphase flow model and experimental verification. In this regard, this study proposes an enhanced discrete phase model for multiphase flow simulation of blood flow with shear stress. This simulation is based on the discrete phase model (DPM). According to the multiphase flow characteristics of blood, a virtual mass force model and a pressure gradient influence model are added to the calculation of cell particle motion. In the experimental verification, nozzle models were designed to simulate the flow with shear stress, varying the degree of shear stress through different nozzle sizes. The microscopic flow was measured by the Particle Image Velocimetry (PIV) experimental method. The comparison of the turbulence models and the verification of the simulation accuracy were carried out based on the experimental results. The result demonstrates that the simulation effect of the SST k-ω model is better than other standard turbulence models. Accuracy analysis proves that the simulation results are accurate and can capture the movement of cell-level particles in the flow with shear stress. The results of the research are conducive to obtaining accurate and comprehensive analysis results in the equipment development phase.

STRUCTURAL DESIGN AND NUMERICAL SIMULATION OF THE DIFFUSER FOR MAGLEV AXIAL BLOOD PUMP

Hydraulic performance is an especially important factor for maglev axial blood pumps that have been used in patients with heart disease. Most maglev axial blood pumps basically consist of a straightener, an impeller and a diffuser. The diffuser plays a key role in the performance of the maglev axial blood pump to provide an adequate pressure head and increase the hydraulic efficiency. Maglev axial blood pumps with various structural diffusers exhibit different hydraulic performance. In this study, computational fluid dynamics (CFD) analysis was performed to quantify hydrodynamic in a maglev axial blood pump with a flow rate of 6 L/min against a pressure head of 100 mmHg to optimize the diffuser structure. First, we design the prototype of diffuser structure based on traditional design method, establish blood flow channel models using commercial software ANSYS FLUENT. Specifically, compare the performance of pump with the diffusers of different parameters, such as the leading edge blade angle, blade-thickness and blade-number. The results show that the diffuser structures with the thickening blade by arc airfoil law, blade-number of 6, leading edge blade angle of 24°, and trailing edge blade angle of 90° exhibited the best hydraulic performance which could be utilized in the optimization design of maglev axial blood pumps.

NUMERICAL STUDIES OF AN AXIAL FLOW BLOOD PUMP WITH DIFFERENT DIFFUSER DESIGNS

Most axial flow blood pumps basically consist of a straightener, an impeller, and a diffuser. The diffuser plays a very important role in the performance of the pump to provide an adequate pressure head and to increase the hydraulic efficiency. During the development of an axial flow blood pump, irregular flow field near the diffuser hub is not desirable as it may induce thrombosis. In order to avoid this phenomenon, two approaches were adopted. In the first approach, the number of the diffuser blades was increased from three (B3, baseline model) to five (B5 model). It was observed that the flow field was improved, but the irregular flow patterns were not completely eliminated. In the second approach, we detached the blades from the diffuser hub (B3C2 model), which was integrated and rotated with the impeller hub. It was found that the rotary diffuser hub significantly improved the flow field, especially near the diffuser hub. Besides the detailed flow fields, the hydraulic and hematologic performances at various flow conditions were also estimated using computational fluid dynamics (CFD). Although each design has its own advantages and disadvantages, the B5 model was superior based on a comparative overview.