*2.4. Boundary Conditions*

For the boundary conditions, the different flow rates (from 5 L/min to 25 L/min) measured in the vitro study [19,20] (Figure 2) were considered for the inlet condition (ventricular side), and the zero static pressure was set as outlet condition (aorta side) [21]. The density and dynamic viscosity of blood were set to 1055 kg/m3 and 0.0035 Pa·s, respectively. Because the influence of the change of pressure and velocity boundary conditions on the phenomenon of leaflet fluttering is not clear, only part of the cardiac cycle was selected for simulation. The total transient simulation time was controlled, ranging from the 200th ms to the 500th ms in one cardiac cycle (Figure 2), and the 300 ms time was discretized with 1500 steps corresponding to a time step of 0.2 ms.

**Figure 2.** Flow rate and leaflet motion throughout one cardiac cycle.
