A combined experimental and computational study of the flow characteristics in a Type B aortic dissection: Effect of primary and secondary tear size
CHEMICAL ENGINEERING RESEARCH & DESIGN
Authors: Zadrazil, Ivan; Corzo, Crispin; Voulgaropoulos, Victor; Markides, Christos N.; Xu, Xiao Yun
Abstract
Aortic dissection is related to the separation of the tunica intima from the aortic wall, which can cause blood to flow through the newly formed lumen, thereby further damaging the torn vessel. This type of pathology is the most common catastrophic event that affects the aorta and is associated with complications such as malperfusion. In this work, an idealised, simplified geometric model of Type B aortic dissection is investigated experimentally using particle image velocimetry (PIV) and numerically using computational fluid dynamic (CFD) simulations. The flow characteristics through the true and false lumina are investigated parametrically over a range of tear sizes. Specifically, four different tear sizes and size ratios are considered, each representing a different dissection case or stage, and the experimental and numerical results of the flow-rate profiles through the two lumina in each case, along with the phase-averaged velocity vector maps at mid-acceleration, mid-deceleration, relaminarisation and peak systole, and their corresponding velocity profiles are compared. The experimental and numerical results are in good qualitative as well as quantitative agreement. The flow characteristics found here provide insight into the importance of the re-entry tear. We observe that an increase in the re-entry tear size increases considerably the flow rate in the false lumen, decreases significantly the wall shear stress (WSS) and decreases the pressure difference between the false and the true lumen. On the contrary, an increase in the entry tear, increases the flow rate through the false lumen, increases slightly the WSS and increases the pressure difference between the false and the true lumen. These are crucial findings that can help interpret medical diagnosis and accelerate prevention and treatment, especially in high-risk patients. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Elliptic supersonic jet morphology manipulation using sharp-tipped lobes
PHYSICS OF FLUIDS
Authors: Rao, Srisha M. V.; Karthick, S. K.; Anand, Abhinav
Abstract
Elliptic nozzle geometry is attractive for mixing enhancement of supersonic jets. However, jet dynamics, such as flapping, gives rise to high-intensity tonal sound. We experimentally manipulate the supersonic elliptic jet morphology by using two sharp-tipped lobes. The lobes are placed on either end of the minor axis in an elliptic nozzle. The design Mach number and the aspect ratio of the elliptic nozzle and the lobed nozzle are 2.0 and 1.65. The supersonic jet is exhausted into ambient under almost perfectly expanded conditions. Time-resolved schlieren imaging, longitudinal and cross-sectional planar laser Mie scattering imaging, planar Particle Image Velocimetry (PIV), and near-field microphone measurements are performed to assess the fluidic behavior of the two nozzles. Dynamic Mode Decomposition (DMD) and proper orthogonal decomposition analyses are carried out on the schlieren and the Mie scattering images. Mixing characteristics are extracted from the Mie scattering images through the image processing routines. The flapping elliptic jet consists of two dominant DMD modes, while the lobed nozzle has only one dominant mode, and the flapping is suppressed. Microphone measurements show the associated noise reduction. The jet column bifurcates in the lobed nozzle enabling a larger surface contact area with the ambient fluid and higher mixing rates in the near-field of the nozzle exit. The jet width growth rate of the two-lobed nozzle is about twice that of the elliptic jet in the near-field, and there is a 40% reduction in the potential core length. PIV contours substantiate the results.