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TECHNICAL PAPERS: Fluids/Heat/Transport

A Numerical and Experimental Investigation of Transitional Pulsatile Flow in a Stenosed Channel

[+] Author and Article Information
N. Beratlis, B. Parvinian, K. Kiger

Department of Mechanical Engineering,  University of Maryland, College Park, MD 20742

E. Balaras1

Department of Mechanical Engineering,  University of Maryland, College Park, MD 20742

1

Corresponding author.

J Biomech Eng 127(7), 1147-1157 (Aug 15, 2005) (11 pages) doi:10.1115/1.2073628 History: Received January 26, 2005; Revised July 29, 2005; Accepted August 15, 2005

In the present paper, a closely coupled numerical and experimental investigation of pulsatile flow in a prototypical stenotic site is presented. Detailed laser Doppler velocimetry measurements upstream of the stenosis are used to guide the specification of velocity boundary conditions at the inflow plane in a series of direct numerical simulations (DNSs). Comparisons of the velocity statistics between the experiments and DNS in the post-stenotic area demonstrate the great importance of accurate inflow conditions, and the sensitivity of the post-stenotic flow to the disturbance environment upstream. In general, the results highlight a borderline turbulent flow that sequentially undergoes transition to turbulence and relaminarization. Before the peak mass flow rate, the strong confined jet that forms just downstream of the stenosis becomes unstable, forcing a role-up and subsequent breakdown of the shear layer. In addition, the large-scale structures originating from the shear layer are observed to perturb the near wall flow, creating packets of near wall hairpin vortices.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the experimental setup

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Figure 2

(a) Schematic of the computational box; (b) Cartesian gird in the vicinity of the stenosis at an x−z plane. Note that the top part of the figure is not drawn to scale.

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Figure 3

Experimental results. (a) Reynolds number variation during the pulsatile cycle: 엯 experiment;– – –theoretical prediction based on a purely sinusoidal pressure gradient. (b) Profiles of the axial velocity, ũ, at x∕H=−10. (c) Profiles of urms″ at x∕H=−10. 엯, t̂1=2π; ◻, t̂2=0.86π; ×, t̂3=1.52π; ◇, t̂4=2π.

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Figure 4

(a) z locations of the inflection points of the streamwise velocity profiles at the inflow plane as a function of the phase angle; (b) profiles of urms″ at x∕H=−13 for instances in the cycle noted by the vertical lines in (a). 엯, t̂1=0.9π; ◻, t̂2=1.3π; ◇, t̂3=1.75π.

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Figure 5

Phase-averaged statistics of the streamwise velocity at t̂∼3∕2π. 엯 experiment, — case 2, –.– case 3. (a) ũ; (b) urms″.

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Figure 6

Phase-averaged statistics of the streamwise velocity at t̂∼2π. 엯 experiment, — case 2, –.– case 3. (a) ũ; (b) urms″.

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Figure 7

Phase-averaged statistics of the streamwise velocity at t̂∼π. 엯 experiment, — Case 2 –.– case 3. (a) ũ; (b) urms″.

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Figure 8

Time average velocity statistics at x∕H=2, x∕H=4, x∕H=6. ⋯⋯ case 1; — case 2;–.– case 4;– – – case 5.

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Figure 9

(Color) Contours of phase-averaged spanwise vorticity and turbulent kinetic energy for case 2. (a) t̂∼−0.4π; (b) t̂∼−0.2π; (c) t̂∼0; (d) t̂∼0.5π; (e) t̂∼π. Here t̂=0 corresponds to maximum flowrate and +∕− signs indicate the amount of time after or prior that instant, respectively.

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Figure 10

(Color) Spatiotemporal evolution of the phase-averaged statistics of the skin friction coefficient. (a) c̃f, top wall; (b) cf″, top wall; (c) c̃f, bottom wall; (d) cf″, bottom wall. The dashed line corresponds to c̃f=0. Phase=0 corresponds to maximum flowrate and +∕− signs indicate the amount of time after or prior that instant, respectively.

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