Sensitivity and downstream influence of the impinging leading-edge vortex instability in a bileaflet mechanical heart valve

Abstract

Bileaflet mechanical heart valves (BMHV) create unphysiological turbulent flow. Such turbulent flow involves multiple instability mechanisms interacting with one another in a confined geometry. For instance, an impinging leading-edge vortex (ILEV) instability creates disturbances at the leading edge of the valve leaflets, while potentially promoting turbulence downstream of the BMHV (Zolfaghari and Obrist, Phys. Rev. Fluids, vol. 4, 2019). In this article, we use adjoint-based methods to study the structural sensitivity of the ILEV instability in the BMHV, and to quantify the role of this instability in the maximum disturbance energy growth in the wake of the BMHV. We first present a direct numerical simulation to show the effect of the ILEV instability on the turbulent flow in the wake of the valve. Second, we perform a modal linear stability analysis on a two-dimensional subdomain attached to the leading edge of one leaflet. We investigate the sensitivity of the global modes associated with this flow using their adjoints, and then show a passive control scenario using a local feedback source. This results in a partial improvement in the flow oscillations downstream of the leaflets. We finally present a non-modal approach to identify the optimal initial conditions for achieving maximum energy growth at arbitrary locations. We show that, for sufficiently large times, the optimal initial condition for highest energy growth in the wake points at the leading edge, which includes the ILEV instability. Our study illustrates that an improved leading-edge shape can effectively reduce turbulence in the wake of the BMHV.

HPC+ in the medical field: Overview and current examples

“…The use of such accelerated codes allows us to go beyond classical forward simulations and to employ, e.g., adjoint-based methods of automatic design optimization for heart valves [ 23 ] or data assimilation to enhance clinical diagnostic imaging [ 25 ]. In particular, the second example presents an application which can connect daily clinical work in a hospital to HPC.…”

Wall shear stress and pressure patterns in aortic stenosis patients with and without aortic dilation captured by high-performance image-based computational fluid dynamics

“…The solver has been optimized for task parallelism on multicore distributed memory supercomputers [35] as well as for combined data-and taskparallelism on multicore-manycore GPU-based hybrid-node supercomputers [19,36]. It has been utilized for a range of challenging laminar-turbulent transition flow scenarios [35,[37][38][39][40]. The GPU-accelerated version of the solver which is up to two orders of magnitude faster than the CPU-based paralllel solver, is particularly favourable for ultimate usage in a clinical setting, as it reduces a single-beat simulation time from months to 1-3 days at the resolution levels used in this work, using only 8 GPUs.…”

Instability mechanisms initiating laminar–turbulent transition past bioprosthetic aortic valves

“…Instabilities initiating turbulent flow around MHVs were evaluated by simplification of the problem with a bottom-up approach and a geometrical submodel (Zolfaghari & Obrist 2019; Zolfaghari et al. 2022). Highly-resolved two- and three-dimensional direct numerical simulations (DNS) were performed for a rigid, fixed MHV in open systolic position.…”