Dynamic Behaviour due to Pulsatile Boundary Conditions in Rotodynamic Blood Pumps

Abstract

Rotodynamic blood pumps (RBPs) provide a therapeutic solution for patients with congestive heart failure who are ineligible for transplantation or require bridging support while awaiting a transplant. While static Computational Fluid Dynamics (CFD) simulations are commonly used to predict flow conditions and ensure the avoidance of blood damage, they do not accurately represent realistic conditions. Since RBPs are directly connected to the cardiovascular interface, they operate in a highly dynamic and transient manner. The aim of this study was to establish a framework for transient CFD simulations to capture the realistic boundary conditions set by the cardiovascular interface. These investigations were carried out for the HeartMate III. To adequately distinguish the effects of static and transient simulations, various methodologies - such as interface modeling, impeller positioning, turbulence, motion modeling, and surface roughness - were initially investigated in a static context and validated with in-vitro results. Pulsatile boundary conditions representing tandem operation with the native heart were subsequently applied in the CFD simulations. The effects of turbulence, motion modeling, speed fluctuations, and time steps were investigated numerically, while the inlet flow conditions were examined experimentally. The simulation setups were validated with dynamic in-vitro results. Although the deviation between experimental and numerical results for the static operation could not be identified (73.6 mmHg vs. 82.7 mmHg at 4.5 l/min and 5400 rpm), questions regarding the interface’s position, turbulence modelling and surface roughness could be clarified. The dynamic behavior resulting from pulsatile boundary conditions can be accurately simulated if static errors are properly accounted for, emphasizing the importance of precise static simulations across the entire flow rate range. Additionally, the methodology combining a moving reference frame with a mixing plane performed as effectively as the sliding mesh approach for time steps up to 36 deg, offering the potential to reduce computational costs.