Some new aspects of the slow flow of a viscous fluid through an axisymmetric duct expansion or contraction. II ? Experimental part

Monnet, P.; Menard, C.; Sigli, D.

doi:10.1007/bf00388666

Cited by 13 publications

(7 citation statements)

References 10 publications

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“…6. This observation is in agreement with the conclusions of the studies focused on creeping sudden expansion flows by Monnet et al (1982) and Macagno and Hung (1967) in larger tubes, d [ 20 mm. In order to ensure that the tracer particles, used for visualization, have no disturbing effect in this regime, experimental tests were also performed with 1 lm diameter particles for e = 1.96 in the range of 0 \ Re d \ 50.…”

Section: Flow Characteristicssupporting

confidence: 92%

“…6 that L r approximately asymptotes to L r^0 .28 at lower Reynolds numbers for e = 1.96, while it reaches L r^0 .15 for e = 1.51. These measurements agree favorably with the results of Monnet et al (1982) and Macagno and Hung (1967) for e = 2.26 and e = 2 who reported asymptotic values of L r ! 0:3 and L r !…”

Section: Flow Characteristicssupporting

confidence: 92%

“…The transition Reynolds number Re tr , which can be considered as the threshold for the onset of the linear trends in laminar sudden expansion flows, was observed to increase when decreasing the expansion ratio. Although not covered in this study, it is worth mentioning that Monnet et al (1982) observed another distinct flow pattern at even lower Reynolds numbers Re d \ 1 in which the inlet jet does not detach from the wall at the expansion but instead follows the step, resulting in the separation angle of b = 0.…”

Section: Flow Characteristicsmentioning

confidence: 83%

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Sudden expansions in circular microchannels: flow dynamics and pressure drop

Khodaparast

Borhani

Thome

2014

Microfluid Nanofluid

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Micro particle shadow velocimetry is used to study the flow of water through microcircular sudden expansions of ratios e = 1.51 and e = 1.96 for inlet Reynolds numbers Re d \ 120. Such flows give rise to annular vortices, trapped downstream of the expansions. The dependency of the vortex length on the Reynolds number Re d and the expansion ratio e is experimentally investigated in this study. Additionally, the shape of the axisymmetric annular vortex is quantified based on the visualization results. These measurements favorably follow the trends reported for larger scales in the literature. Redevelopment of the confined jet to the fully developed Poiseuille flow downstream of the expansion is also studied quantitatively. Furthermore, the experimentally resolved velocities are used to calculate high resolution static pressure gradient distributions along the channel walls. These measurements are then integrated into the axisymmetric momentum and energy balance equations, for the flow downstream of the expansion, to obtain the irreversible pressure drop in this geometry. As expected, the measured pressure drop coefficients for the range of Reynolds numbers studied here do not match the predictions of the available empirical correlations, which are commonly based turbulent flow studies. However, these results are in excellent agreement with previous numerical calculations. The pressure drop coefficient is found to strongly depend on the inlet Reynolds number for Re d \ 50. Although no lengthscale effect is observed for the range of channel diameters studied here, for Reynolds numbers Re d \ 50, which are typical in microchannel applications, complex nonlinear trends in the flow dynamics and pressure drop measurements are discovered and discussed in this work.

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Section: Flow Characteristicssupporting

confidence: 92%

Section: Flow Characteristicssupporting

confidence: 92%

Section: Flow Characteristicsmentioning

confidence: 83%

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Sudden expansions in circular microchannels: flow dynamics and pressure drop

Khodaparast

Borhani

Thome

2014

Microfluid Nanofluid

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“…Even if the geometry differs from a smooth expansion, one would expect the presence of similar phenomena. Monnet, Menard & Sigli (1982) studied the flow through a cylindrical duct in the vicinity of a section discontinuity for very small Reynolds numbers. The evolution of the stationary vortex cell was analysed using visualization techniques.…”

Section: Introductionmentioning

confidence: 99%

Asymmetry and transition to turbulence in a smooth axisymmetric constriction

et al. 2008

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The flow through a smooth axisymmetric constriction (a stenosis in medical applications) of 75% restriction in area is measured using stereoscopic and time-resolved particle image velocimetry (PIV) in the Reynolds number range Re ~ 100–1100. At low Reynolds numbers, steady flow results reveal an asymmetry of the flow downstream of the constriction. The jet emanating from the throat of the nozzle is deflected towards the wall causing the formation of a one-sided recirculation region. The asymmetry results from a Coanda-type wall attachment already observed in symmetric planar sudden expansion flows. When the Reynolds number is increased above the critical value of 400, the separation surface cannot remain attached and an unsteady flow regime begins. Low-frequency axial oscillations of the reattachment point are observed along with a slow swirling motion of the jet. The phenomenon is linked to a periodic discharge of the unstable recirculation region inducing alternating laminar and turbulent flow phases. The resulting flow is highly non-stationary and intermittent. Discrete wavelet transforms are used to discriminate between the large-scale motions of the mean flow and the vortical and turbulent fluctuations. Continuous wavelet transforms reveal the spectral structure of flow disturbances. Temporal measurements of the three velocity components in cross-sections are used with the Taylor hypothesis to qualitatively reconstruct the three-dimensional velocity vector fields, which are validated by comparing with two-dimensional PIV measurements in meridional planes. Visualizations of isosurfaces of the swirling strength criterion allow the identification of the topology of the vortices and highlight the formation and evolution of hairpin-like vortex structures in the flow. Finally, with further increase of the Reynolds number, the flow exhibits less intermittency and becomes stationary for Re ~ 900. Linear stochastic estimation identifies the predominance of vortex rings downstream of the stenosis before breakdown to turbulence.

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“…Experiments and predictions demonstrated that, for semidense sudden expansion flows, particle dispersion is mainly controlled by the relative magnitude of the time elapsed between successive collisions, the local value of the particle relaxation time, and the eddy time scale. e details of laminar axisymmetric sudden expansion flows such as the distance to the reattachment, redevelopment length, and strength of the recirculating flow have also been widely investigated through a flow visualization technique [12,13] and particle image velocimetry (PIV) measurements [14]. ese results are useful in solving some practical problems.…”

Section: Introductionmentioning

confidence: 99%

Computational Study of Gas‐Solid Flow in a Horizontal Stepped Pipeline

Chu

Pan

et al. 2019

Mathematical Problems in Engineering

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In this paper, the mechanism governing the particle-fluid flow characters in the stepped pipeline is studied by the combined discrete element method (DEM) and computational fluid dynamics (CFD) model (CFD-DEM) and the two fluid model (TFM). The mechanisms governing the gas-solid flow in the horizontal stepped pipeline are investigated in terms of solid and gas velocity distributions, pressure drop, process performance, the gas-solid interaction forces, solid-solid interaction forces, and the solid-wall interaction forces. The two models successfully capture the key flow features in the stepped pipeline, such as the decrease of gas velocity, solid velocity, and pressure drop, during and after the passage of gas-solid flow through the stepped section. What is more important, the reason of the appearance of large size solid dune and pressure surge phenomena suffered in the stepped pipeline is investigated macroscopically and microscopically. The section in which the blockage problem most likely occurs in the stepped pipeline is confirmed. The pipe wall wearing problem, which is one of the most common and critical problems in pneumatic conveying system, is analysed and investigated in terms of interaction forces. It is shown that the most serious pipe wall wearing problem happened in the section which is just behind the stepped part.

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Some new aspects of the slow flow of a viscous fluid through an axisymmetric duct expansion or contraction. II ? Experimental part

Cited by 13 publications

References 10 publications

Sudden expansions in circular microchannels: flow dynamics and pressure drop

Sudden expansions in circular microchannels: flow dynamics and pressure drop

Asymmetry and transition to turbulence in a smooth axisymmetric constriction

Computational Study of Gas‐Solid Flow in a Horizontal Stepped Pipeline

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