Current and past research projects

Patient-specific modeling of a neonatal patient with truncus arteriosus and quadricuspid valve

Segmentation of CT imaging to create pre- and postoperative patient anatomy

Quadricuspid valve construction via elasticity-based design [Kaiser et al.]

Fluid-structure interaction simulations [Griffith et al.] to evaluate valve performance

Prediction of in vivo valve performance and elimination of valve regurgitation after truncus arteriosus repair without direct leaflet intervention 

Global stability analysis applied to three-dimensional flow field downstream of fluttering and non-fluttering bioprosthetic aortic valve 

Higher growth rates of instabilities downstream of non-fluttering valve

Transient growth analysis to identify optimal initial perturbations maximizing energy gain

Perturbations generated by vortical structures closely resembling those observed in fully coupled nonlinear fluid–structure interaction simulations 

Optimal perturbations may initiate the shear-layer instabilities responsible for transition to turbulence

Laminar-turbulent transition downstream of fluttering and non-fluttering bioprosthetic aortic valve design

Fluttering valve

• triangular starting vortex

• periodical vortex shedding consistent with fluttering frequency

• streamwise vortex pairs above valve commissures

Non-fluttering valve

• round/hexagonal starting vortex

• small-scale vortices due to flow separation at curved open leaflets

Fluid–structure interaction simulations for generic aortic geometries with fluttering bioprosthetic aortic valve design

1. flexible leaflets / base aortic geometry

2. flexible leaflets / narrow aortic geometry

3. fixed open leaflets / base aortic geometry

Interaction between starting vortex, counter-rotating streamwise vortices and periodic vortex rings leads to nonlinear breakdown to small-scale vortices 

No fluttering alters vortex formation and results in lower turbulence levels

Modal analysis shows that (1) transition in non-fluttering valve governed by azimuthal mode of wavenumber 6, (2) fluttering motion promotes mode of wavenumber 3 and suppresses higher modes

Linear stability analysis and FSI simulations of simplified valve model to study mechanisms of laminar–turbulent transition

Modified Orr–Sommerfeld equations with FSI model indicate Kelvin–Helmholtz and FSI instabilities for physiological Re numbers

FSI simulations confirm the growth rates and phase speeds of these instabilities

Eigenmodes associated with leaflet kinematics allow for decoupled oscillations

Starting vortex interacts with the aortic wall leading to secondary vortex moving towards the shear layer in the leaflet wake

Earlier onset of instability in narrow aorta

Shear layer instability onset followed by leaflet motion onset leading to vortex shedding and nonlinear breakdown of flow 

Growing perturbations of the shear layer instability propagate upstream and may initiate the FSI instabilities on leaflets

Lagrangian particle tracing to compute platelet activation indices for assessing thombosis risk in larger aortic roots with and without neo-sinus

Larger aorta may be associated with higher risk for transcatheter heart valve thrombosis

Higher platelet activation levels in larger aorta

Less efficient sinus washout in larger aorta

Highest platelet activation for particles stagnating in neo-sinus of larger aorta