Flow Dynamics in a Model of a Left Ventricle with Different Mitral Valve Orientations

The formation of vortex rings at valve leaflets during ventricular inflow has been a topic of interest for many years. It is generally accepted nowadays that the purpose of vortex rings is to conserve energy, reduce the workload on the heart, and minimize particle residence time. We investigated these claims by testing three different levels of annulus angle for the mitral valve: a healthy case, a slightly angled case (20°), and a highly angled case (46°). Circulation was determined to be reversed in the non-healthy case, with a dominant counterclockwise rotation instead of clockwise. Viscous energy dissipation was highest in the slightly angled case, followed by the healthy case and then the highly angled case. A Lagrangian analysis demonstrated that the healthy case resulted in the least amount of stasis, requiring eight cardiac cycles to evacuate 99% of initial ventricle volume compared to the 16 and 13 cardiac cycles required by the slightly angled and highly angled cases, respectively.

A Multiscale Numerical Modeling Study of Smoke Dispersion and the Ventilation Index in Southwestern Colorado

The ventilation index (VI) is an index that describes the potential for smoke or other pollutants to disperse from a source. In this study, a Lagrangian particle dispersion model was utilized to examine smoke dispersion and the diagnostic value of VI during a September 2018 prescribed fire in southwestern Colorado. Smoke dispersion in the vicinity of the fire was simulated using the FLEXPART-WRF particle dispersion model, driven by meteorological outputs from Advanced Regional Prediction System (ARPS) simulations of the background (non-fire) conditions. Two research questions are posed: (1) Is a horizontal grid spacing of 4 km comparable to the finest grid spacing currently used in operational weather models and sufficient to capture the spatiotemporal variability in wind and planetary boundary layer (PBL) structure during the fire? (2) What is the relationship between VI and smoke dispersion during the prescribed fire event, as measured by particle residence time within a given horizontal or vertical distance from each particle’s release point? The ARPS no-fire simulations are shown to generally reproduce the observed variability in weather variables, with greatest fidelity to observations found with horizontal grid spacing of approximately 1 km or less. It is noted that there are considerable differences in particle residence time (i.e., dispersion) at different elevations, with VI exhibiting greater diagnostic value in the southern half of the domain, farthest from the higher terrain across the north. VI diagnostic value is also found to vary temporally, with diagnostic value greatest during the mid-morning to mid-afternoon period, and lowest during thunderstorm outflow passage in the late afternoon. Results from this study are expected to help guide the application of VI in complex terrain, and possibly inform development of new dispersion potential metrics.