scholarly journals The dam-break problem for concentrated suspensions of neutrally buoyant particles

2013 ◽  
Vol 724 ◽  
pp. 95-122 ◽  
Author(s):  
C. Ancey ◽  
N. Andreini ◽  
G. Epely-Chauvin
Keyword(s):  
Velocity Profile ◽  
Newtonian Fluid ◽  
Velocity Profiles ◽  
Lubrication Theory ◽  
Dam Break ◽  
Particle Migration ◽  
Flow Depth ◽  
Concentrated Suspensions ◽  
Front Position ◽  
Neutrally Buoyant

AbstractThis paper addresses the dam-break problem for particle suspensions, that is, the flow of a finite volume of suspension released suddenly down an inclined flume. We were concerned with concentrated suspensions made up of neutrally buoyant non-colloidal particles within a Newtonian fluid. Experiments were conducted over wide ranges of slope, concentration and mass. The major contributions of our experimental study are the simultaneous measurement of local flow properties far from the sidewalls (velocity profile and, with lower accuracy, particle concentration) and macroscopic features (front position, flow depth profile). To that end, the refractive index of the fluid was adapted to closely match that of the particles, enabling data acquisition up to particle volume fractions of 60 %. Particle migration resulted in the blunting of the velocity profile, in contrast to the parabolic profile observed in homogeneous Newtonian fluids. The experimental results were compared with predictions from lubrication theory and particle migration theory. For solids fractions as large as 45 %, the flow behaviour did not differ much from that of a homogeneous Newtonian fluid. More specifically, we observed that the velocity profiles were closely approximated by a parabolic form and there was little evidence of particle migration throughout the depth. For particle concentrations in the 52–56 % range, the flow depth and front position were fairly well predicted by lubrication theory, but taking a closer look at the velocity profiles revealed that particle migration had noticeable effects on the shape of the velocity profile (blunting), but had little impact on its strength, which explained why lubrication theory performed well. Particle migration theories (such as the shear-induced diffusion model) successfully captured the slow evolution of the velocity profiles. For particle concentrations in excess of 56 %, the macroscopic flow features were grossly predicted by lubrication theory (to within 20 % for the flow depth, 50 % for the front position). The flows seemed to reach a steady state, i.e. the shape of the velocity profile showed little time dependence.

Characterization of Transition to Turbulence for Blood in a Straight Pipe Under Steady Flow Conditions

2016 ◽  
Vol 138 (7) ◽  
Author(s):  
Dipankar Biswas ◽  
David M. Casey ◽  
Douglas C. Crowder ◽  
David A. Steinman ◽  
Yang H. Yun ◽  
...  
Keyword(s):  
Velocity Profile ◽  
Steady Flow ◽  
Newtonian Fluid ◽  
Fluid Velocity ◽  
Shear Thinning ◽  
Velocity Profiles ◽  
Transition To Turbulence ◽  
Pipe Diameter ◽  
Flow Conditions ◽  
Straight Pipe

Blood is a complex fluid that, among other things, has been established to behave as a shear thinning, non-Newtonian fluid when exposed to low shear rates (SR). Many hemodynamic investigations use a Newtonian fluid to represent blood when the flow field of study has relatively high SR (>200 s−1). Shear thinning fluids have been shown to exhibit differences in transition to turbulence (TT) compared to that of Newtonian fluids. Incorrect prediction of the transition point in a simulation could result in erroneous hemodynamic force predictions. The goal of the present study was to compare velocity profiles near TT of whole blood and Newtonian blood analogs in a straight rigid pipe with a diameter 6.35 mm under steady flow conditions. Rheology was measured for six samples of whole porcine blood and three samples of a Newtonian fluid, and the results show blood acts as a shear thinning non-Newtonian fluid. Measurements also revealed that blood viscosity at SR = 200 s−1 is significantly larger than at SR = 1000 s−1 (13.8%, p < 0.001). Doppler ultrasound (DUS) was used to measure velocity profiles for blood and Newtonian samples at different flow rates to produce Reynolds numbers (Re) ranging from 1000 to 3300 (based on viscosity at SR = 1000 s−1). Two mathematically defined methods, based on the velocity profile shape change and turbulent kinetic energy (TKE), were used to detect TT. Results show similar parabolic velocity profiles for both blood and the Newtonian fluid for Re < 2200. However, differences were observed between blood and Newtonian fluid velocity profiles for larger Re. The Newtonian fluid had blunt-like velocity profiles starting at Re = 2403 ± 8 which indicated transition. In contrast, blood did not show this velocity profile change until Re = 2871 ± 104. The Newtonian fluid had large velocity fluctuations (root mean square (RMS) > 20%) with a maximum TKE near the pipe center at Re = 2316 ± 34 which indicated transition. In contrast, blood results showed the maximum TKE at Re = 2806 ± 109. Overall, the critical Re was delayed by ∼20% (p < 0.001) for blood compared to the Newtonian fluid. Thus, a Newtonian assumption for blood at flow conditions near transition could lead to large errors in velocity prediction for steady flow in a straight pipe. However, these results are specific to this pipe diameter and not generalizable since SR is highly dependent on pipe diameter. Further research is necessary to understand this relation in different pipe sizes, more complex geometries, and under pulsatile flow conditions.

scholarly journals The dam-break problem for viscous fluids in the high-capillary-number limit

2009 ◽  
Vol 624 ◽  
pp. 1-22 ◽  
Author(s):  
C. ANCEY ◽  
S. COCHARD ◽  
N. ANDREINI
Keyword(s):  
Capillary Number ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Similarity Solutions ◽  
Dam Break ◽  
Navier Stokes ◽  
Flow Depth ◽  
Visualization System ◽  
Depth Profiles ◽  
Front Position

Experiments were undertaken to investigate dam-break flows where a finite volume of highly viscous fluid (glucose with viscosity μ ≈ 350 Pa s) maintained behind a lock gate was released into a horizontal or inclined flume. The resulting sequence of flow-depth profiles was tracked using a three-dimensional visualization system. In the low-Reynolds-number and high-capillary-number limits, analytical solutions can be obtained from the Navier–Stokes equations using lubrication theory and matched asymptotic expansions. At shallow slopes, similarity solutions can also be worked out. While the variation in the front position scaled with time as predicted by theory for both horizontal and sloping flumes, there was a systematic delay in the front position observed. Moreover, taking a closer look at the experimental flow-depth profiles shows that they were similar, but they noticeably deviated from the theoretical similarity form for horizontal planes. For sloping beds, the flow-depth profile is correctly predicted provided that different scalings are used at shallow and large slopes.

Suspensions with a tunable effective viscosity: a numerical study

2012 ◽  
Vol 693 ◽  
pp. 345-366 ◽  
Author(s):  
L. Jibuti ◽  
S. Rafaï ◽  
P. Peyla
Keyword(s):  
Effective Viscosity ◽  
Volume Fraction ◽  
Numerical Study ◽  
Spherical Particles ◽  
Dimensionless Number ◽  
Particle Rotation ◽  
Concentrated Suspensions ◽  
Sheared Suspensions ◽  
Neutrally Buoyant ◽  
Universal Behaviour

AbstractIn this paper, we conduct a numerical investigation of sheared suspensions of non-colloidal spherical particles on which a torque is applied. Particles are mono-dispersed and neutrally buoyant. Since the torque modifies particle rotation, we show that it can indeed strongly change the effective viscosity of semi-dilute or even more concentrated suspensions. We perform our calculations up to a volume fraction of 28 %. And we compare our results to data obtained at 40 % by Yeo and Maxey (Phys. Rev. E, vol. 81, 2010, p. 62501) with a totally different numerical method. Depending on the torque orientation, one can increase (decrease) the rotation of the particles. This results in a strong enhancement (reduction) of the effective shear viscosity of the suspension. We construct a dimensionless number $\Theta $ which represents the average relative angular velocity of the particles divided by the vorticity of the fluid generated by the shear flow. We show that the contribution of the particles to the effective viscosity can be suppressed for a given and unique value of $\Theta $ independently of the volume fraction. In addition, we obtain a universal behaviour (i.e. independent of the volume fraction) when we plot the relative effective viscosity divided by the relative effective viscosity without torque as a function of $\Theta $. Finally, we show that a modified Faxén law can be equivalently established for large concentrations.

scholarly journals New Infrared Diffuse Interstellar Bands in the Galactic Center and Elsewhere

2013 ◽  
Vol 9 (S297) ◽  
pp. 64-67
Author(s):  
T. R. Geballe
Keyword(s):  
Velocity Profile ◽  
Galactic Center ◽  
Velocity Profiles ◽  
Significant Fraction ◽  
Diffuse Interstellar Bands ◽  
The Galaxy ◽  
Band Spectra

AbstractThis paper updates the recent discovery of over a dozen new diffuse interstellar bands (DIBs), first in H-band spectra of stars in the Galactic center (GC) and toward stars in the Cygnus OB2 Association. The H-band DIBs, which currently number 15, are the longest wavelength DIBs reported to date and are the first found on sightlines toward the Galactic center. K-band (2.0-2.5 μm) spectra of the GC stars do not reveal additional DIBs. Comparison of the velocity profile of the strongest of the new DIBs in the sightline toward GCS3-2 (in the GC) with that toward Cygnus OB2 No. 9 and also with the broad velocity profiles of H3+ lines toward GCS3-2 confirm that a significant fraction of the diffuse material producing the DIB absorptions on sightlines to the GC is located within the central few hundred parsecs of the Galaxy.

scholarly journals Identification for control of suspended objects in non-Newtonian fluids

2019 ◽  
Vol 22 (5) ◽  
pp. 1378-1394 ◽  
Author(s):  
Isabela Birs ◽  
Cristina Muresan ◽  
Dana Copot ◽  
Ioan Nascu ◽  
Clara Ionescu
Keyword(s):  
Newtonian Fluid ◽  
Pulsatile Flow ◽  
Controller Design ◽  
Velocity Profiles ◽  
Navier Stokes ◽  
Flow Conditions ◽  
Dynamic Flow ◽  
Fluid Environment ◽  
Flow Changes ◽  
Identification For Control

Abstract This paper proposes a framework for modelling velocity profiles and suspended objects in non-Newtonian fluid environment. A setup is proposed to allow mimicking blood properties and arterial to venous dynamic flow changes. Navier-Stokes relations are employed followed by fractional constitutive equations for velocity profiles and flow. The theoretical analysis is performed under assumptions of steady and pulsatile flow conditions, with incompressible properties. The fractional derivative model for velocity and friction drag effect upon a suspended object are determined. Experimental data from such an object is then recorded in real-time and identification of a fractional order model performed. The model is determined from step input changes during pulsatile flow for velocity in the direction of the flow. Further on, this model can be employed for controller design purposes for velocity and position in pulsatile non-Newtonian fluid flow.

Velocity Profiles of Turbulent Boundary Layers

1969 ◽  
Vol 73 (698) ◽  
pp. 143-147 ◽  
Author(s):  
M. K. Bull
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Velocity Profile ◽  
Boundary Layers ◽  
Experimental Work ◽  
Constant Pressure ◽  
Velocity Profiles ◽  
Turbulent Boundary Layers ◽  
Boundary Layer Equations

Although a numerical solution of the turbulent boundary-layer equations has been achieved by Mellor and Gibson for equilibrium layers, there are many occasions on which it is desirable to have closed-form expressions representing the velocity profile. Probably the best known and most widely used representation of both equilibrium and non-equilibrium layers is that of Coles. However, when velocity profiles are examined in detail it becomes apparent that considerable care is necessary in applying Coles's formulation, and it seems to be worthwhile to draw attention to some of the errors and inconsistencies which may arise if care is not exercised. This will be done mainly by the consideration of experimental data. In the work on constant pressure layers, emphasis tends to fall heavily on the author's own data previously reported in ref. 1, because the details of the measurements are readily available; other experimental work is introduced where the required values can be obtained easily from the published papers.

Effect of Tapering on Pulsatile Flow Through a U-Tube Model of the Human Aortic Arch

2010 ◽  
Author(s):  
Masaru Sumida
Keyword(s):  
Velocity Profile ◽  
Pulsatile Flow ◽  
Velocity Profiles ◽  
Cross Sectional Area ◽  
Flow Rate Ratio ◽  
Sectional Area ◽  
Cross Sectional ◽  
Turn Angle ◽  
Flow Through ◽  
The Cross

An experimental investigation of pulsatile flow through a tapered U-tube was performed to study the blood flow in the aorta. The experiments were carried out in a U-tube with a curvature radius ratio of 3.5 and a 50% reduction in the cross-sectional area from the entrance to the exit of the curved section. Velocity measurements were conducted by a laser Doppler velocimetry for a Womersley number of 10, a mean Dean number of 400 and a flow rate ratio of 1. The velocity profiles for pulsatile flow in the tapered U-tube were compared with the corresponding results in a U-tube having a uniform cross-sectional area. The striking effects of the tapering on the flow are exhibited in the axial velocity profiles in the section from the latter half of the bend to the downstream tangent immediately behind the bend exit. A depression in the velocity profile appears at a smaller turn angle Ω in the case of tapering, although the magnitude of the depression relative to the cross-sectional average velocity decreases. The value of β, which indicates the uniformity in the velocity profile over the cross section, decreases with increasing Ω, whereas it rapidly increases immediately behind the bend exit.

Flow Development in a Circular Duct With a Highly Distorted Inlet Condition

2007 ◽  
Author(s):  
Srinivas Badam ◽  
Jie Cui ◽  
Stephen Idem
Keyword(s):  
Numerical Model ◽  
Velocity Profile ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Pressure Gradients ◽  
Development Length ◽  
Circular Duct ◽  
Inlet Velocity ◽  
Inlet Condition ◽  
Flow Development

The development of air flow downstream of a stationary fan located in a circular duct was investigated. The objective of the research was to study the evolution of the velocity profiles and pressure gradients at various axial locations. The velocity profiles were measured at three different Reynolds numbers using a five-hole directional probe. Because the stationary fan caused the inlet velocity profile to be highly distorted, it was determined experimentally that the development length exceeded 20 duct diameters. Since this was greater than the length of the apparatus, a corresponding numerical model of the flow was generated using the commercial CFD software Fluent-6.1/6.2. The numerical model was validated against the experimental results. The hydrodynamic development length was therein determined numerically.

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