Absolute instability of impinging leading edge vortices in a submodel of a bileaflet mechanical heart valve

Zolfaghari, Hadi; Obrist, Dominik (2019). Absolute instability of impinging leading edge vortices in a submodel of a bileaflet mechanical heart valve. Physical review fluids, 4(12) American Physical Society 10.1103/PhysRevFluids.4.123901

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Bileaflet mechanical heart valves (BMHVs) have been related to the production of unphysiological turbulent flow in the ascending aorta. These valves comprise a pair of rigid blunt plates (leaflets), which are immersed in a confined flow with Reynolds numbers up to 10 000. They are prone to develop impinging leading-edge vortex (ILEV) instabilities [K. Hourigan et al., J. Fluids Struct. 15, 387 (2001); S. Deniz and T. Staubli, J. Fluids Struct. 11, 3 (1997)] on the leaflets because of their relatively large chord-to-thickness ratio and their low angle of incidence. These instabilities can produce strong disturbances between the leaflets which may contribute to the onset and intensity of turbulent flow in the wake of the valve. The complex nature of the flow around BMHVs prevents a detailed theoretical analysis of the underlying instability mechanisms. Therefore, we defined a two-dimensional submodel of the flow with fixed leaflets, which renders the problem accessible to the rich toolbox of hydrodynamic stability theory. High-order numerical simulations of this flow configuration indicated the systolic development of unstable ILEVs on the inner side of the leaflets during systolic acceleration of the flow. We found that the ILEV instabilities can only be observed with sufficiently high spatial resolution, which may explain why these phenomena have not been observed so far in most computational studies of BMHV flow. Orr-Sommerfeld eigenmodes with high growth rates confirmed the unstable character of this flow. We further identified a pocket of absolute instability which acts as a wave maker between the leaflets. Finally, we confirmed that this wave-maker region has a direct effect on the nonlinear breakdown in the wake of the valve. To this end, the leaflet geometry was modified such that the ILEV (and the associated wave maker) was eliminated and it was shown numerically that the wake remains laminar for the modified geometry. The results of this study are a first step toward a detailed understanding of the hydrodynamic instability mechanisms which lead to turbulent flow past BMHVs.

Item Type:

Journal Article (Original Article)

Division/Institute:

10 Strategic Research Centers > ARTORG Center for Biomedical Engineering Research > ARTORG Center - Cardiovascular Engineering (CVE)

Graduate School:

Graduate School for Cellular and Biomedical Sciences (GCB)

UniBE Contributor:

Zolfaghari, Hadi and Obrist, Dominik

Subjects:

500 Science > 530 Physics
600 Technology > 610 Medicine & health
600 Technology > 620 Engineering

ISSN:

2469-990X

Publisher:

American Physical Society

Language:

English

Submitter:

Hadi Zolfaghari

Date Deposited:

23 Dec 2019 15:17

Last Modified:

23 Dec 2019 15:22

Publisher DOI:

10.1103/PhysRevFluids.4.123901

Additional Information:

Editor's Suggestion Article. Featured in Physics Magazine.

BORIS DOI:

10.7892/boris.136313

URI:

https://boris.unibe.ch/id/eprint/136313

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