Abstract Imagebased computational fluid dynamics (CFD) has become a new capability for determining wall stresses of pulsatile flows. However, a computational platform that directly connects image information to pulsatile wall stresses is lacking. Prevailing methods rely on manual crafting of a hodgepodge of multidisciplinary software packages, which is usually laborious and errorprone. We present a new computational platform, to compute wall stresses in imagebased pulsatile flows using the volumetric lattice Boltzmann method (VLBM). The novelty includes: (1) a unique image processing to extract flow domain and local wall normality, (2) a seamless connection between image extraction and VLBM, (3) an enroute calculation of strainrate tensor, and (4) GPU acceleration (not included here). We first generalize the streaming operation in the VLBM and then conduct application studies to demonstrate its reliability and applicability. A benchmark study is for laminar and turbulent pulsatile flows in an imagebased pipe (Reynolds number: 10 to 5000). The computed pulsatile velocity and shear stress are in good agreements with Womersley's analytical solutions for laminar pulsatile flows and concurrent laboratory measurements for turbulent pulsatile flows. An application study is to quantify the pulsatile hemodynamics in imagebased human vertebral and carotid arteries including velocity vector, pressure, and wallshear stress. The computed velocity vector fields are in reasonably well agreement with MRA (magnetic resonance angiography) measured ones. This computational platform is good for imagebased CFD with medical applications and porescale porous media flows in various natural and engineering systems.
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Incompressible active phases at an interface. Part 1. Formulation and axisymmetric odd flows
Inspired by the recent realization of a twodimensional (2D) chiral fluid as an active monolayer droplet moving atop a 3D Stokesian fluid, we formulate mathematically its freeboundary dynamics. The surface droplet is described as a general 2D linear, incompressible and isotropic fluid, having a viscous shear stress, an active chiral driving stress and a Hall stress allowed by the lack of timereversal symmetry. The droplet interacts with itself through its driven internal mechanics and by driving flows in the underlying 3D Stokes phase. We pose the dynamics as the solution to a singular integral–differential equation, over the droplet surface, using the mapping from surface stress to surface velocity for the 3D Stokes equations. Specializing to the case of axisymmetric droplets, exact representations for the chiral surface flow are given in terms of solutions to a singular integral equation, solved using both analytical and numerical techniques. For a discshaped monolayer, we additionally employ a semianalytical solution that hinges on an orthogonal basis of Bessel functions and allows for efficient computation of the monolayer velocity field, which ranges from a nearly solidbody rotation to a unidirectional edge current, depending on the subphase depth and the Saffman–Delbrück length. Except in the nearwall limit, these solutions have divergent surface shear stresses at droplet boundaries, a signature of systems with codimensionone domains embedded in a 3D medium. We further investigate the effect of a Hall viscosity, which couples radial and transverse surface velocity components, on the dynamics of a closing cavity. Hall stresses are seen to drive inward radial motion, even in the absence of edge tension.
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 NSFPAR ID:
 10400882
 Date Published:
 Journal Name:
 Journal of Fluid Mechanics
 Volume:
 951
 ISSN:
 00221120
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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