Fluid dynamics in the human heart: Altered vortex formation and wash-out in mitral regurgitation simulations

Mitral regurgitation alters the flow conditions in the left ventricle. To account for quantitative changes and to investigate the behavior of different flow components, a realistic computational model of the whole human heart was employed in this study. While performing fluid dynamics simulations, a scalar transport equation was solved to analyze vortex formation and ventricular wash-out for different regurgitation severities. Additionally, a particle tracking algorithm was implemented to visualize single components of the blood flow. We confirmed a significantly lowered volume of the direct flow component as well as a higher vorticity in the diseased case.

Visualization of submerged turbulent jets using particle tracking velocimetry

Over the past few decades, advances have been made in using particle image velocimetry (PIV) and particle tracking velocimetry (PTV) for mapping of Lagrangian velocity and acceleration flow fields. With PIV, Lagrangian trajectories are not measured directly; rather, hypothetical trajectories must be constructed from sequences of Eulerian velocity snapshots. Because PTV directly measures actual trajectories, it provides distinct advantages over PIV, especially for trajectories with abrupt changes in direction. In this work, a novel particle tracking algorithm is described, then applied to track trajectories of tracer particles in submerged turbulent jets. The Reynolds numbers ranged from 1000 to 25,000, thereby covering laminar, transitioning-to-turbulence, and fully turbulent flow regimes. The novel particle tracking algorithm is designed to handle flows with very high particle concentrations, thereby resolving small-scale flow structures. Trajectories are tracked with high velocity gradients, sharp curvatures, cycloids, abrupt changes in direction, and strong recirculation—all of which are inaccessible via construction from PIV sequences. Most trajectories measured in this work are at least 500 camera frames (time steps) long, with many being more than 3000 frames long. Graphic abstract

Dust Particle Tracking at Comet 67P/Churyumov–Gerasimenko

<p>We present the newest iteration of our particle tracking algorithm and highlight findings based on its application to different data sets. The intended use of the algorithm is to analyze image sequences taken by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) of the Rosetta spacecraft during the outbound perihelion phase of comet 67P/Churyumov-Gerasimenko. During this active phase, a lot of material was being ejected, in part as relatively large, boulder-sized objects (dm to m). With our work, we hope to better understand the processes that are responsible for the ejection and those that might affect the flight path of the particles once they are lifted. </p>