20 research outputs found
The effects of stabilizing and destabilizing longitudinal curvature on the structure of turbulent, two-stream mixing layers
The construction and development of the multi-component traversing system and associated control hardware and software are presented. A hydrogen bubble/laser sheet flow visualization technique was developed to visually study the characteristics of the mixing layers. With this technique large-scale rollers arising from the Taylor-Gortler instability and its interaction with the primary Kelvin-Helmholtz structures can be studied
The influence of physiological flow development on popular wall shear stress metrics in an idealized curved artery
We numerically investigate the influence of flow development on secondary
flow patterns and subsequent wall shear stress distributions in a curved artery
model, and we compute vascular metrics commonly used to assess variations in
blood flow characteristics as it applies to arterial disease. We model a human
artery with a simple, rigid 180-degree curved tube with circular cross-section
and constant curvature, neglecting effects of taper, torsion and elasticity.
High-fidelity numerical results are computed from an in-house discontinuous
spectral element flow solver. The flow rate used in this study is
physiological. We perform this study using a Newtonian blood-analog fluid
subjected to a pulsatile flow with two inflow conditions. The first flow
condition is fully developed while the second condition is undeveloped (i.e.
uniform). We observe and discuss differences in secondary flow patterns that
emerge over the rapid acceleration and deceleration phases of the physiological
waveform, and we directly connect the variation in intensity of these secondary
flow patterns along the curvature to differences in the wall shear stress
metrics for each entrance condition. Results indicate that decreased axial
velocities under an undeveloped condition produce less intense secondary flow
that, in turn, reduces both the oscillatory and multidirectional nature of the
wall shear stress vector, and we link this effect to abnormalities in computed
stress metrics. These results suggest potentially lower prevalence of disease
in curvatures where entrance flow is rather undeveloped-a physiologically
relevant result to further understand the influence of blood flow development
on disease.Comment: 10 pages, 10 figures. arXiv admin note: text overlap with
arXiv:2108.0237
Shannon Entropy-Based Wavelet Transform Method for Autonomous Coherent Structure Identification in Fluid Flow Field Data
The coherent secondary flow structures (i.e., swirling motions) in a curved artery model possess a variety of spatio-temporal morphologies and can be encoded over an infinitely-wide range of wavelet scales. Wavelet analysis was applied to the following vorticity fields: (i) a numerically-generated system of Oseen-type vortices for which the theoretical solution is known, used for bench marking and evaluation of the technique; and (ii) experimental two-dimensional, particle image velocimetry data. The mother wavelet, a two-dimensional Ricker wavelet, can be dilated to infinitely large or infinitesimally small scales. We approached the problem of coherent structure detection by means of continuous wavelet transform (CWT) and decomposition (or Shannon) entropy. The main conclusion of this study is that the encoding of coherent secondary flow structures can be achieved by an optimal number of binary digits (or bits) corresponding to an optimal wavelet scale. The optimal wavelet-scale search was driven by a decomposition entropy-based algorithmic approach and led to a threshold-free coherent structure detection method. The method presented in this paper was successfully utilized in the detection of secondary flow structures in three clinically-relevant blood flow scenarios involving the curved artery model under a carotid artery-inspired, pulsatile inflow condition. These scenarios were: (i) a clean curved artery; (ii) stent-implanted curved artery; and (iii) an idealized Type IV stent fracture within the curved artery