Abstract

Heart failure is a cardiovascular disease, which affects millions of people worldwide. If the heart failure is too severe, a heart transplantation is the gold standard for treatment. Unfortunately, a significant shortage of donor hearts exists worldwide. A technical solution to overcome this gap between demand and availability are Ventricular Assist Devices (VADs). The VADs are almost always implanted within the body of the patient and assist the weak heart by creating the needed pressure to sufficiently supply the circulatory systems.

The device must be designed in such a way that the VAD's operating range can maintain the blood flow in the circulatory system. For this purpose, a defined pressure head ${\displaystyle H}$ must be built up at a certain blood flow rate ${\displaystyle Q}$. Whether a VAD design meets these fluid mechanical requirements can be checked by flow simulations in the pre-clinical evaluation. Furthermore, a VAD must be designed for highest hemocompatibility, which means that the blood components in the flow are not damaged due to non-physiological flow conditions. This can be checked by analysing the fluid dynamical stresses ${\displaystyle \tau }$ through flow simulations feeding them into a numerical blood damage prediction model (yielding the hemodynamical parameters as described later).

In this context, the present ERCOFTAC KB Wiki entry examines the flow field in a VAD computed by flow simulations. A highly turbulence-resolving large-eddy simulation (LES) is compared as a reference with an unsteady Reynolds-averaged Navier-Stokes simulation (URANS) using a ${\displaystyle k}$-${\displaystyle \omega }$-SST turbulence model (standard simulation setup by industry for VAD simulations). First, the performed simulations are validated using the experimentally determined pressure heads. Afterwards, the results of both simulation methods are compared with respect to the computed fluid mechanical and hemodynamical parameters. In particular, the question to what extent URANS can reproduce the fluid mechanical parameters (head, efficiency) and hemodynamical parameters (shear stresses and blood damage predictions) compared to the reference LES shall be answered.

Instantaneous vortical structures in the simulated flow domain of the considered axial VAD. Visualised with the Q-criterion [1]. The shown flow field was simulated by the LES at the nominal operation point of the VAD.

Contributed by: Benjamin Torner — University of Rostock, Germany