| A left ventricular assist device (LVAD) is a mechanical pump that can effectively relieve some strain from a native heart that has been weakened by disease or damage, and increase blood flow supplied to the body to maintain normal physiologic function. The clinical effectiveness of LVADs has been demonstrated; however, all of the currently available pumps are approved and only as temporary treatment because of either the damage that they cause to blood or their limited mechanical design life. A magnetically suspended rotary blood pump offers the potential to meet the requirements of both extended design life and negligible blood damage.; The fluid dynamics within a centrifugal LVAD determines the overall pump performance and potentially contributes to both hemolysis (red blood cell damage) and thrombosis (blood clotting). The flow within the pump is three-dimensional, turbulent, and time varying (unlike most industrial pumps), due to the beating of the heart and passing of impeller blades.; In order to characterize the flow within the University of Virginia LVAD for both steady and pulsatile flow, measurements using Particle Image Velocimetry (PIV) were made. A prototype pump that allows for optical access has been designed and built. The internal flow paths are identical to a version of the pump that has been used in animal implant tests and has been modeled extensively with CFD. Measurements of mean velocity and some turbulence statistics were made within several regions of the pump including the inlet, blade passage, exit volute, and diffuser. Phase-averaged measurements were made to characterize the time varying flow due to both the heartbeat and blade passage.; Measurements were used to identify regions of potential blood damage due to high shear stress and or stagnation of the blood based on a comparison of experimental measurements to published data. Although levels of viscous and Reynolds shear stress everywhere within the pump are below threshold values for damage to red cells, the flow field may promote activation of the clotting cascade. A quantitative assessment of current numerical CFD models (including turbulence models) based on a comparison of experimental and computed data sets is included. |
