Pulsatile flow through constricted tubes: an experimental investigation using photochromic tracer methods

Abstract

A photochromic tracer method has been used to record pulsatile flow velocity profiles simultaneously at three axial locations along a flow channel. Two major advantages of this multiple-trace method are that it enables velocity data to be acquired in an efficient non-invasive manner and that it provides a detailed description of the spatial relationship of the flow field. The latter is found to be particularly useful in the investigation of transitional type flows; for example, in describing coherent flow structures. Studies of the flow patterns in tubes with mild to moderate degrees of vessel constriction were performed using a 2.9 Hz sinusoidal flow superimposed on a steady flow (frequency parameter of 7.5; mean and modulation Reynolds numbers of 575 and 360, respectively). With mild constrictions (< 50% area reduction), isolated regions of vortical and helical structures were observed primarily during the deceleration phase of the flow cycle and in the vicinity of the reattachment point. As expected, these effects were accentuated when the constriction was asymmetric. For moderate constrictions (50%–80%), transition to turbulence was triggered just before peak flow through the breakdown of waves and streamwise vortices that were shed in the high-shear layer. During this vortex generation phase of the flow cycle, the wall shear stress fluctuated quite intensely, especially in the vicinity of the reattachment point, and its instantaneous value increased by at least a factor of eight. Such detailed descriptions of the transition to turbulence and of the spatial and temporal variation of the wall shear stress, particularly near the reattachment point, have not been previously reported for pulsatile flow through constricted tubes. The observed wall shear stress variations support a proposal by Mao & Hanratty (1986) of an interaction of the imposed flow oscillation with the turbulent fluctuations within the viscous sublayer.

Neutrophil Adhesion on Endothelial Cells in a Novel Asymmetric Stenosis Model: Effect of Wall Shear Stress Gradients

“…In these experiments, an identical cast model to the cell culture model was perfused with a solution of odorless mineral spirits (Shell-Sol 715) and trace amounts of colourless dye (1′,3′,3′-trimethylindoline-6-nitro-benzospiropyran). When exposed to UV light from a laser, the solution turns opaque and forms a photochromic trace (21)(22)(23)(24). A CCD camera (Dalsa Pantera TF IM60, Dalsa) and an image-processing board (National Instruments PCI 1428) were used to track the molecular displacement and calculate the wall shear rate.…”

Evaluating the Effect of Magnetic Field, Impulse Flow and Gravity Acceleration on Different Femoral Bypass Angles in Order to Remove Lipid Accumulations in Atherosclerosis Disease by Simulation Method

“…Sankar presented a developed analysis of impulsive flow affection by a turbulence method that via associating their results with ours it is concluded that for every value of index, in some points of the pulse which the velocity was high, maximum shear stress increased and vice versa (in some points of the pulse with a low velocity, maximum shear stress was decreased). These results revealed that impulsive flow can cause returned flow (in maximum discharge) after the obstruction which calculating the amounts seems to be necessary to optimize bypass surgical operations 16 .…”

Effect of Pulsatile Flow Waveform and Womersley Number on the Flow in Stenosed Arterial Geometry

“…We have expressed the pulsatility in the flow through a variation in Reynolds number [14,45] around a mean Reynolds number (Re mean ) of 200. The Reynolds number (Re = ρud/μ) is defined on the basis of the diameter of the unstenosed artery, time-averaged mean velocity of flow, and the density and viscosity of blood, which are taken as ρ = 1056 Kg/m 3 and μ = .00345 PaS, respectively.…”

“…Ahmed and Giddens [16] used ultrasound and laser Doppler techniques to analyze the flow disturbances and wall shear stress associated with the presence of stenoses. The photochromic tracer method used by Ojha et al [14] enabled the description of coherent flow structures present in the pulsatile poststenotic flow field. Siouffi et al [17] and Deplano and Siouffi [18] used the pulsed Doppler ultrasonic velocimetry for the measurement of velocity and determination of wall shear stress around the zone of stenosis, while Brunette et al [19] used particle image velocimetry to find out the wall shear stress distribution and secondary flow associated with a mild stenosis in a phantom coronary artery.…”

“…However, most experimental and numerical studies assumed a simple harmonic pulse upstream to the stenosis [14,16,25,37]. Johnston et al [26] and Wiwatanapataphee et al [38] performed their studies with physiological waveforms observed in the human right coronary artery, while Long et al [39] considered the volumetric flow waveform in the carotid artery, measured by the Doppler ultrasound.…”