Investigation of turbulent flow field in maglev centrifugal blood pumps of CH-VAD and Heartmate III using large-eddy simulation

Abstract

Maglev bearings can avoid serious blood damage caused by mechanical bearings, and has become the primary trend of blood pumps. Maglev blood pumps allow a relatively large clearance to improve blood washout and reduce the stress inside the clearance so that blood damage can be reduced. Nonetheless, large clearances also lead to high secondary flow and turbulence intensity, causing further blood damage. This study aims to conduct a thorough analysis of flow fields in two typical maglev blood pumps, the CH-VAD and Heartmate III which feature distinct designs of secondary flow path and impeller (semi-open versus closed impeller) using large eddy simulation (LES) with a focus on the secondary flows and their interaction with the main flows. LES was found to be superior to the Reynolds-averaged Navier-Stokes (RANS) method in predicting performance curves. At high flow rate (8L/min), the efficiency of CH-VAD remains high compared with 5 L/min, while the efficiency of Heartmate III drops considerably. The wide clearance in Heartmate III induced high secondary flow and flow loss, leading to an large incidence angle at both working conditions. The high viscous stress inside the clearances is the major cause of flow loss and potential blood damage in CH-VAD. This study shows that Maglev bearings dose not guarantee good blood compatibility, clearances should be designed based on trade-offs among high shear stress inside smaller clearance, and strong recirculations caused by larger clearances. This study provides useful reference for the design and optimization of maglev blood pumps.