Flow of Urine Through the Ureter: A Collapsible, Muscular Tube Undergoing Peristalsis

1989 ◽  
Vol 111 (3) ◽  
pp. 206-211 ◽  
Author(s):  
D. J. Griffiths
Keyword(s):  
Flow Rate ◽  
Reynolds Numbers ◽  
Muscular Contraction ◽  
Critical Value ◽  
Mean Flow ◽  
Low Reynolds Numbers ◽  
Collapsible Tubes ◽  
Ureteral Peristalsis ◽  
Steady Propagation ◽  
Peristaltic Contractions

In steady flow through nonuniform collapsible tubes a key concept is the compressive zone, at which flow limitation can occur at both high and low Reynolds numbers. Ureteral peristalsis can be considered as a series of compressive zones, corresponding to waves of active muscular contraction, that move at near-constant speed along the ureter towards the bladder. One-dimensional, lubrication-theory analysis shows that peristalsis can pump urine from kidney into the bladder only at relatively low mean rates of urine flow. Under these circumstances isolated boluses of urine are propelled steadily through the ureter (assumed uniform) by the contraction waves. At higher mean rates of flow the behavior depends on whether the frequency of peristalsis is higher or lower than a critical value. For frequencies above the critical value steady propagation of boluses that are in contact with contraction waves at both ends is possible. As the flow rate rises the urine begins to leak through the contraction waves and steady peristaltic flow breaks down. There is an upper limit to the mean flow rate that can be carried by steady peristalsis, which depends on the mechanical properties of the ureter. At high flow rates the peristaltic contractions do not pump but hinder the flow of urine through the ureter.

The effect of waves on subgrid-scale stresses, dissipation and model coefficients in the coastal ocean bottom boundary layer

2007 ◽  
Vol 583 ◽  
pp. 133-160 ◽  
Author(s):  
W. A. M. NIMMO SMITH ◽  
J. KATZ ◽  
T. R. OSBORN
Keyword(s):  
Dynamic Model ◽  
Energy Flux ◽  
Correlation Coefficients ◽  
Reynolds Numbers ◽  
Subgrid Scale ◽  
Mean Flow ◽  
Low Reynolds Numbers ◽  
Induced Motion ◽  
Stress Models ◽  
Wave Induced

Six sets of particle image velocimetry (PIV) data from the bottom boundary layer of the coastal ocean are examined. The data represent periods of high, moderate and weak mean flow relative to the amplitude of wave-induced motion, which correspond to high, moderate and low Reynolds numbers based on the Taylor microscale (Re). The two-dimensional PIV velocity distributions enable spatial filtering to calculate some of the subgrid-scale (SGS) stresses, from which we can estimate the SGS dissipation, and evaluate the performance of typically used SGS stress models. The previously reported mismatch between the SGS and viscous dissipation at moderate and low Reynolds numbers appears to be related to the sparsity of large vortical structures that dominate energy fluxes.Conditional sampling of SGS stresses and dissipation based on wave phase using Hilbert transforms demonstrate persistent and repeatable direct effects of large-scale but weak straining by the waves on the SGS energy flux at small scales. The SGS energy flux is phase-dependent, peaking when the streamwise-wave-induced velocity is accelerating, and lower when this velocity is decelerating. Combined with strain rate generated by the mean flow, the streamwise wave strain causes negative energy flux (backscatter), whereas the vertical wave strain causes a positive flux. The phase-dependent variations and differences between horizontal and vertical contributions to the cascading process extend to strains that are substantially higher than the wave-induced motion. These trends may explain the measured difference between spatial energy spectra of streamwise velocity fluctuations and spectra of the wall-normal component, i.e. the formation of spectral bumps in the spectra of the streamwise component at the wavenumbers for the transition between inertial and dissipation scales.All the model coefficients of typical SGS stress models measured here are phase dependent and show similar trends. Thus, the variations of measured SGS dissipation with phase are larger than those predicted by the model variables. In addition, the measured coefficients of the static Smagorinsky SGS stress model decrease with decreasing turbulence levels, and increase with filter size. The dynamic model provides higher correlation coefficients than the Smagorinsky model, but the substantial fluctuations in their values indicate that ensemble averaging is required. The ‘global’ dynamic model coefficients indicate that the use of a scale-dependent dynamic model may be appropriate. The structure function model yields poor correlation coefficients and is found to be over-dissipative under all but the highest turbulence levels. The nonlinear model has higher correlations with measured stresses, as expected, but it also does not reproduce the trends with wave phase.

Steady Flow Through a Double Converging-Diverging Tube Model for Mild Coronary Stenoses

1989 ◽  
Vol 111 (3) ◽  
pp. 212-221 ◽  
Author(s):  
S. C. van Dreumel ◽  
G. D. C. Kuiken
Keyword(s):  
Pressure Drop ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Tube Model ◽  
Mean Flow ◽  
Number Range ◽  
Low Reynolds Numbers ◽  
In Series ◽  
Coronary Stenoses ◽  
Converging Angle

Velocity profiles and the pressure drop across two mild (62 percent) coronary stenoses in series have been investigated numerically and experimentally in a perspex-tube model. The mean flow rate was varied to correspond to a Reynolds number range of 50–400. The pressure drop across two identical (62 percent) stenoses show that for low Reynolds numbers the total effect of two stenoses equals that of two single stenoses. A reduction of 10 percent is found for the higher Reynolds numbers investigated. Numerical and experimental results obtained for the velocity profiles agree very well. The effect of varying the converging angle of a single mild (62 percent) coronary stenosis on the fluid flow has been determined numerically using a finite element method. Pressure-flow relation, especially with respect to relative short stenoses, is discussed.

An investigation of turbulent plane Couette flow at low Reynolds numbers

1995 ◽  
Vol 286 ◽  
pp. 291-325 ◽  
Author(s):  
Knut H. Bech ◽  
Nils Tillmark ◽  
P. Henrik Alfredsson ◽  
Helge I. Andersson
Keyword(s):  
Couette Flow ◽  
Reynolds Stress ◽  
Reynolds Numbers ◽  
Wall Turbulence ◽  
Turbulence Structure ◽  
Plane Couette Flow ◽  
Mean Flow ◽  
Low Reynolds Numbers ◽  
Low Reynolds ◽  
Near Wall

The turbulent structure in plane Couette flow at low Reynolds numbers is studied using data obtained both from numerical simulation and physical experiments. It is shown that the near-wall turbulence structure is quite similar to what has earlier been found in plane Poiseuille flow; however, there are also some large differences especially regarding Reynolds stress production. The commonly held view that the maximum in Reynolds stress close to the wall in Poiseuille and boundary layer flows is due to the turbulence-generating events must be modified as plane Couette flow does not exhibit such a maximum, although the near-wall coherent structures are quite similar. For two-dimensional mean flow, turbulence production occurs only for the streamwise fluctuations, and the present study shows the importance of the pressure—strain redistribution in connection with the near-wall coherent events.

scholarly journals Effect of the inlet flow rate ratio on liquid efficiency in a T-shaped micromixer at low Reynolds numbers

2020 ◽  
Vol 1677 ◽  
pp. 012138
Author(s):  
A Yu Kravtsova ◽  
M V Kashkarova ◽  
P E Ianko ◽  
A V Bilsky ◽  
Y V Kravtsov
Keyword(s):  
Flow Rate ◽  
Rate Ratio ◽  
Reynolds Numbers ◽  
Flow Rate Ratio ◽  
Inlet Flow ◽  
Low Reynolds Numbers ◽  
Inlet Flow Rate ◽  
Low Reynolds

Assessing Uncertainties in Friction Factor Measurement as a Tool in Devising Experimental Set-Ups

2007 ◽  
Author(s):  
Marco Lorenzini ◽  
Gian Luca Morini ◽  
Torsten Henning ◽  
Juergen J. Brandner
Keyword(s):  
Pressure Drop ◽  
Friction Factor ◽  
Flow Rate ◽  
Volume Flow Rate ◽  
Reynolds Numbers ◽  
Laminar Regime ◽  
Total Uncertainty ◽  
Low Reynolds Numbers ◽  
More Care ◽  
Factor Measurement

The promising performance of microchannels has given rise to intensive research on pressure drop and heat transfer characteristics of flows at the small- validate new ones, experiments need to be conducted, which are particularly difficult given the characteristic dimensions involved and the magnitude of the fluxes to be measured. Although more care has been devoted lately to the design of experiments in terms of control of geometry and boundary conditions, the uncertainties which inevitably affect each measurement do not seem to have been given the proper consideration. Correctly calculating uncertainties not only allow to a correct assessment of the experimental data obtained, but can also be used to decide which measurements need to have the highest precision to achieve a certain accuracy, thus saving money on the others. In this paper, a quantitative criterion is given to assess the accuracy achievable in the determination of the friction factor in the laminar regime for the flow of a fluid in a circular microtube. The influence of the six quantities (pressure drop, outlet pressure, temperature, length, pressure and volume flow rate) measured to determine f in the laminar regime are studied separately and when combined. It is found that at low Reynolds numbers flow rate and pressure drop measurements are determinant for the final value of the uncertainty, while at larger Reynolds numbers the influence of the accuracy in measuring the hydraulic diameter prevails and also limits the minimum value that the total uncertainty can take.

Unsteady numerical investigation of two different corrugated airfoils

2016 ◽  
Vol 231 (13) ◽  
pp. 2423-2437 ◽  
Author(s):  
WH Ho ◽  
TH New
Keyword(s):  
Large Scale ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Mean Flow ◽  
Airfoil Surface ◽  
Low Reynolds Numbers ◽  
Corrugated Surfaces ◽  
Large Scale Flow ◽  
Lift And Drag

An unsteady, two-dimensional numerical study was conducted to investigate the aerodynamic and flow characteristics of two bio-inspired corrugated airfoils at Re = 14,000 and compared with those of a smooth NACA0010 airfoil. Mean aerodynamic results reveal that the corrugated airfoils have better lift performance compared to the NACA0010 airfoil but incur slightly higher drag penalty. Mean flow streamlines indicate that this favourable performance is due to the ability of the corrugated airfoils in mitigating large-scale flow separations and stall. Unsteady flow field results show persistent formations of small recirculating vortices that remain within the corrugations at 10° angle-of-attack or less for one of the corrugated airfoil and below 15° for the other. In contrast, the flow behaviour can be highly turbulent with regular pairings of large-scale flow separation vortices along the upper surface at higher angles-of-attack. This not only disrupts the small recirculating vortices and causes them to detach from the corrugated surfaces, but it gets increasingly dominant at higher angles-of-attack resulting in regular lift and drag oscillations. At the end of each cycle, there is a sudden ejection of flow perpendicular to the airfoil surface and these disruptions manifest themselves as “kinks” in the instantaneous lift and drag of the corrugated airfoils. Therefore instead of regular fluctuations, the lift and drag curves have additional undulations. Despite that, the corrugations are able to produce larger pressure differentials between the upper and lower surfaces than the smooth airfoil. The current study demonstrates the intricate relationships between different sharp surface corrugations and favourable aerodynamic performance. In particular, results from this paper supports earlier investigations that corrugated airfoils may be used to good effects even at low Reynolds numbers, where flow separations are more likely.

Stability of a Column of Rotating Viscous Liquid

1961 ◽  
Vol 57 (1) ◽  
pp. 152-159 ◽  
Author(s):  
J. Gillis
Keyword(s):  
Viscous Liquid ◽  
Reynolds Numbers ◽  
Critical Value ◽  
Wave Number ◽  
Uniform Density ◽  
Low Reynolds Numbers ◽  
Special Cases ◽  
Image Position ◽  
Coefficient Of Viscosity ◽  
Very High

ABSTRACTA long column of viscous liquid of radius a and uniform density p is rotating about its axis with angular velocity ω. It is shown that this motion is stable to plane perturbations of wave number 8 provided that the surface tension T satisfies . This critical value is higher than that required for stability of the similar motion of a nonviscous liquid, but is otherwise independent of the coefficient of viscosity. The rate of development of instability when T is less than the critical value is also studied. Some numerical results are given.The condition has recently been obtained by Hocking (2) for the special cases of very high and very low Reynolds numbers.

scholarly journals Hydrodynamic particle focusing enhanced by femtosecond laser deep grooving at low Reynolds numbers

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tianlong Zhang ◽  
Misuzu Namoto ◽  
Kazunori Okano ◽  
Eri Akita ◽  
Norihiro Teranishi ◽  
...  
Keyword(s):  
Flow Rate ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Low Flow ◽  
Live Cells ◽  
Low Reynolds Numbers ◽  
Particle Focusing ◽  
Human T Cell ◽  
Fs Laser ◽  
Low Reynolds

AbstractMicrofluidic focusing of particles (both synthetic and biological), which enables precise control over the positions of particles in a tightly focused stream, is a prerequisite step for the downstream processing, such as detection, trapping and separation. In this study, we propose a novel hydrodynamic focusing method by taking advantage of open v-shaped microstructures on a glass substrate engraved by femtosecond pulse (fs) laser. The fs laser engraved microstructures were capable of focusing polystyrene particles and live cells in rectangular microchannels at relatively low Reynolds numbers (Re). Numerical simulations were performed to explain the mechanisms of particle focusing and experiments were carried out to investigate the effects of groove depth, groove number and flow rate on the performance of the groove-embedded microchannel for particle focusing. We found out that 10-µm polystyrene particles are directed toward the channel center under the effects of the groove-induced secondary flows in low-Re flows, e.g. Re < 1. Moreover, we achieved continuous focusing of live cells with different sizes ranging from 10 to 15 µm, i.e. human T-cell lymphoma Jurkat cells, rat adrenal pheochromocytoma PC12 cells and dog kidney MDCK cells. The glass grooves fabricated by fs laser are expected to be integrated with on-chip detection components, such as contact imaging and fluorescence lifetime-resolved imaging, for various biological and biomedical applications, where particle focusing at a relatively low flow rate is desirable.

Sign in / Sign up

Export Citation Format

Share Document