Calculation of Dynamic Coefficients for a Magnetically Levitated Artificial Heart Pump Using a CFD Approach

The artificial heart community acknowledges the 3rd generation Ventricular Assist Devices (VADs) as the leading technology in mechanical blood pump development. This category consists of rotary pumps with no mechanical or fluid bearings in contact with the fluid medium, usually magnetic or noncontacting hydrodynamic bearings. A magnetic suspension prevents the rotating impeller from contacting the pump’s internal surfaces and reduces regions of stagnant and high shear flow that normally surround a fluid or mechanical bearing. Magnetic bearings have no moving parts in contact and thus do not wear over time; this generally lengthens the operational life of the pumps as compared to those supported by conventional bearings. Employing this 3rd generation technology, the University of Virginia has been developing a ventricular assist device (LifeFlow) with a rotor that is suspended entirely by magnetic bearings. In order to perform the stability analysis, the hydrodynamic effects of the rotating impeller should be included in the calculation. This study describes the method to calculate the stiffness, damping, and mass coefficients, based on the CFD prediction of radial fluid forces exerted on the impeller due to its eccentric position inside the pump housing over a range of operating conditions. In consideration of the suspension design, the fluid forces exerted on the levitated axial impeller were estimated using CFD such that any fluid perturbations would be accounted for and counterbalanced during the suspension and motor design phase.