Unsteady Character and Flow Fields in an Axial Blood Pump under Pulsatile Pressure Boundary Condition

Abstract

Blood pumps have been widely used as a temporary method for heart failure. In recent years, the challenging factors in design have generally concentrated on how to deal with the complicated time-dependent fluid dynamics. Therefore, this research studies the impact to flow field by pulsatile boundary condition with both steady and unsteady numerical simulations. For steady computation, total pressures of 20, 40, 60, 80, 100mmHg and an average pressure of 120mmHg were given at the inlet and outlet respectively, and an unsteady simulation was then conducted with the same fixed pressure of 120mmHg at the outlet but a periodical sinusoidal pressure within 20 and 100mmHg at the inlet. Compared with a single character line drawn through the steady points, the unsteady computation resulted in a closed elliptic character curve. In the whole range of operation of the unsteady condition, flow field showed a well-attached flow in rotor passage but a large area of recirculation in the second row of stator passages. By contrast, flow field in the first row of stator passages and the pressure on the surface of rotor blades were greatly impacted by the acceleration and deceleration of the flow rate, which can be well explained by the change of incidence. Besides, flow rate acceleration or deceleration exaggerated a non-uniform distribution of velocity, which can easily form a larger area of high scalar shear stress than the steady results. A special pressure distribution between rotors and stators was also observed in unsteady flow.