Numerical Simulation of Flow in Mechanical Heart Valves: Grid Resolution and the Assumption of Flow Symmetry

Abstract

A numerical method is developed for simulating unsteady, 3-D, laminar flow through a bileaflet mechanical heart valve with the leaflets fixed. The method employs a dual-time-stepping artificial-compressibility approach together with overset (Chimera) grids and is second-order accurate in space and time. Calculations are carried out for the full 3-D valve geometry under steady inflow conditions on meshes with a total number of nodes ranging from 4 x 10(5) to 1.6 x 10(6). The computed results show that downstream of the leaflets the flow is dominated by two pairs of counter-rotating vortices, which originate on either side of the central orifice in the aortic sinus and rotate such that the common flow of each pair is directed away from the aortic wall. These vortices intensify with Reynolds number, and at a Reynolds number of approximately 1200 their complex interaction leads to the onset of unsteady flow and the break of symmetry with respect to both geometric planes of symmetry. Our results show the highly 3-D structure of the flow; question the validity of computationally expedient assumptions of flow symmetry; and demonstrate the need for highly resolved, fully 3-D simulations if computational fluid dynamics is to accurately predict the flow in prosthetic mechanical heart valves.

Measurements of steady flow through a bileaflet mechanical heart valve using stereoscopic PIV

“…Similar axisymmetric designs have been used in previous studies and have been shown to reproduce primary flow structures of interest such as strong jet shear layers, and sinus flow recirculation relevant in the clinical setting [5,9,10]. The design, however, does not account for flow complexities associated with flow in three sinuses of Valsalva, or distensible aortic walls.…”

“…In a low Reynolds number CFD simulation, Ge et al [10] found symmetry breaking about the XY plane at Re = 750. It is therefore likely that there was some degree of asymmetry about the XY plane in the current study (where Re = 7600).…”

Stereoscopic PIV of Steady Flow Through a Bileaflet Mechanical Heart Valve

“…The aortic sinus geometry was axisymmetric which has proved useful in CFD validation studies (Ge et al 2003, Dasi et al 2007, Shahbazi 2007. The sinus profile was a b-spline curve generated by Solid Edge V18 and defined by the points given in Table 2 …”

Movement Effects on the Flow Physics and Nutrient Delivery in Engineered Valvular Tissues

“…Ge and Sotiropolus (Ge et al, 2003) were the first to successfully use direct numerical simulations of pulsatile flow through bileaftet mechanical heart valves (BHMV). They simulated blood flow through a BHMV embedded within a straight aortic segment using an IBM approach, and they conducted in vitro studies using a similar experimental set-up.…”

“…We summarize some important milestones in CFD of heart valves and heart valve prostheses here: The flow through a tilting disk in a permanently half open position was simulated using a FEM approach by Shim and Cham (Shim and Chang, 1994). Ge et al (Ge et al, 2005;Ge et al, 2003) performed equations that also accounted for turbulence. King et al (King et al, 1996) described the presence of orifice jets during systole velocities in a CarboMedics® valve.…”