3-D simulation of the St. Jude Medical bileaflet valve opening process: fluid-structure interaction study and experimental validation.

BACKGROUND AND AIM OF THE STUDY

Simulation of the opening and closure dynamics of a mechanical valve through a moving deforming mesh algorithm presents a challenge because of the large rotations of the leaflet and of the small gaps between the housing and the leaflets, which make remeshing a critical issue. The present study offers a computational approach to the simulation of valve leaflet motion during the opening process, together with an experimental set-up for validation of the model.

METHODS

A fully 3-D simulation of the 27 mm St. Jude Medical Hemodynamic Plus mechanical valve was performed using the computational code, Fluent. Interaction between the leaflet and fluid was simulated through customized user subroutines which, according to a weakly coupled approach, update the leaflet velocities through subsequent time steps by means of an under-relaxation procedure. A parallel, experimental test was defined to collect data for the set-up of simulations and for validation purposes.

RESULTS

The computed leaflet velocity and angular displacement compared well with experimental data. The model captured the main features of the opening process, and did so also from a quantitative viewpoint. Nonetheless, some discrepancies were observed, including a delay of approximately 7 ms in the computed leaflet displacement and an underestimation by approximately 7% of the maximum computed leaflet velocity.

CONCLUSION

The weakly coupled approach adopted here limited computational costs, thus allowing the simulation of a fully 3-D realistic mechanical valve within 154 CPU hours at minimal computational costs. No significant drawbacks were raised in comparison with the fully coupled approach. The opening process delay was similar to that reported previously, and cannot be ascribed to the weakly coupled approach adopted here.