scholarly journals Axial creeping flow in the gap between a rigid cylinder and a concentric elastic tube

2016 ◽  
Vol 806 ◽  
pp. 580-602 ◽  
Author(s):  
S. B. Elbaz ◽  
A. D. Gat
Keyword(s):  
Fluid Layer ◽  
Elastic Shell ◽  
Gravity Current ◽  
Travelling Wave ◽  
Elastic Tube ◽  
Creeping Flow ◽  
Shear Stresses ◽  
Length Scales ◽  
Rigid Cylinder ◽  
Viscous Forces

We examine transient axial creeping flow in the annular gap between a rigid cylinder and a concentric elastic tube. The gap is initially filled with a thin fluid layer. We employ an elastic shell model and the lubrication approximation to obtain governing equations for the elastohydrodynamic interaction. At long axial length scales viscous forces are balanced by elastic tension, while at shorter length scales the viscous–elastic balance is achieved by means of an interplay between elastic bending, tension and shear stresses. Based on a viscous gravity current analogy in the tensile–viscous regime, we devise propagation laws for displacement flows which are induced by a variety of boundary conditions and examine different limits of the prewetting thickness. Next we focus on the moving elastohydrodynamic contact line at the edge of a penetrating film. A uniform matched asymptotic solution connecting the interior tension-based region with a boundary layer region near the propagation front is presented. Finally, a constructive example is shown in which isolated moving deformation patterns are created and superimposed to form a travelling wave displacement field. The presented interaction between viscosity and elasticity may be applied to fields such as soft robotics and micro-scale or larger swimmers by allowing for the time-dependent control of an axisymmetric compliant boundary.

Stokes flow past bubbles and drops partially coated with thin films. Part 2. Thin films with internal circulation – a perturbation solution

1983 ◽  
Vol 132 ◽  
pp. 295-318 ◽  
Author(s):  
Robert E. Johnson ◽  
S. S. Sadhal
Keyword(s):  
Thin Films ◽  
Fluid Layer ◽  
Cell Structure ◽  
Creeping Flow ◽  
Immiscible Fluid ◽  
Fluid Viscosity ◽  
Perturbation Scheme ◽  
Bulk Fluid ◽  
Viscous Forces ◽  
Surface Tension Forces

In the present study we examine the steady axisymmetric creeping flow due to the motion of a liquid drop or a bubble which is partially covered by a thin immiscible fluid layer or film. The analysis is based on the assumption that surface-tension forces are large compared with viscous forces which deform the drop, and that the circulation in the film is weak. The latter assumption is satisfied provided that the film-fluid viscosity is not too small. A perturbation scheme based on the thinness of the fluid layer is used to construct the solution.One of the principal results is an expression for the drag force on the complex drop. We also find that the extent to which the drop or bubble is covered the film has a maximum value depending on the magnitude of the driving force on the film. In addition, we find the rather interesting result that when the ratio of the primary drop viscosity and bulk fluid viscosity is greater than ½, the circulation within the film may have a double-cell structure.

Release of ADP from Erythrocytes Under High Shear Stresses in Tube Flow

1979 ◽  
Author(s):  
H. Schmid-Schönbein ◽  
I. Rohling-Winkel ◽  
P. Blasberg ◽  
E. Jüngling ◽  
A. Wehmeyer ◽  
...  
Keyword(s):  
Fluid Layer ◽  
Shape Change ◽  
Total Concentration ◽  
Shear Stresses ◽  
Tube Flow ◽  
High Shear ◽  
Hemoglobin Content ◽  
Before And After ◽  
Adp Release ◽  
Adenosine Nucleotides

ADP stemning from red blood has been shown to “activate platelets” producing shape change, as well as aggregation and release. However, the mode of release of ADP from intact RBC has never been established. Contrary to popular misconceptions, high shear stresses (τ) prevail during natural hemostatic plug formationin arteries and arterioles. Therefore, we tested ADP-release from RBC subjected for 5-100 msec in tube flow (τ-0-200N/m2) during passage through a hollow fiber (0 400 μm, L = 20 cm) with semipermeable walls (AMICON R). Samples from the fluid layer near the wall were ultrafiltered through it and became accessible for chemical analysis. Concentrations of K+, adenosine nucleotides (HPLC), and Hb (In the supernatant) before and after shear exposure were measured. At T > 50 N/m2T K+, adenosine nue Ieotides, and hemoglobin concentrations rose in the supernatant. Only K+ was higher in the u1 trafiltrate than in the latter, whereas total concentration of adenosine nucleotides were not different and hemoglobin did not permeate. There was no difference between the relative molar concentration of total adenosine nucleotides of hemoglobin, i.e. the nucleotides and hemoglobin content of 10-4 and 10-3 of all RBC were liberated. In the ultrafiltrate (ADP) > 2 χ 10-7 M/L, sufficient to activate platelets in the presence of Ca++.

Axial distortion of airways in the lung

1983 ◽  
Vol 54 (1) ◽  
pp. 185-190 ◽  
Author(s):  
M. J. Kallok ◽  
S. J. Lai-Fook ◽  
M. A. Hajji ◽  
T. A. Wilson
Keyword(s):  
Elastic Tube ◽  
Shear Stresses ◽  
Coupling Mechanism ◽  
Airway Wall ◽  
Axial Loads ◽  
Elastic Continuum ◽  
Airway Lumen ◽  
Axial Forces ◽  
Mathematical Analyses ◽  
The Continuum

Axial loads were applied around the circumference of an airway lumen by pulling on a cup-shaped anchor that embedded itself in the airway wall. Axial displacements were measured as a function of distance from the load, and the data were compared to the results of mathematical analyses of continuum mechanics models. In the modeling it was assumed that the elastic tube representing the airway is bonded to the surrounding elastic continuum representing the parenchyma and that axial forces are transmitted between the tube and the continuum by shear stresses at the interface. The agreement between the measured and computed axial displacements supports the hypothesis that the shear stresses are the dominant coupling mechanism. The following quantitative relations between force and displacement were obtained. The axial displacement produced by the load L was approximately 0.05 L/pi alpha mu, where alpha is the airway radius and mu is the shear modulus of the parenchyma. The displacement decayed to approximately one-half this maximal value at two diameters from the load.

scholarly journals An experimental and theoretical study of the dynamics of grounding lines

2013 ◽  
Vol 728 ◽  
pp. 5-28 ◽  
Author(s):  
Samuel S. Pegler ◽  
M. Grae Worster
Keyword(s):  
Theoretical Study ◽  
Fluid Layer ◽  
Gravity Current ◽  
Three Dimensional ◽  
Vertical Shear ◽  
Inviscid Fluid ◽  
West Antarctica ◽  
Full Contact ◽  
Grounding Line ◽  
Longitudinal Extension

AbstractWe present an experimental and theoretical study of a thin, viscous fluid layer that flows radially under gravity from a point source into a denser inviscid fluid layer of uniform depth above a rigid horizontal surface. Near the source, the viscous layer lies in full contact with the surface, forming a vertical-shear-dominated viscous gravity current. At a certain distance from the source, the layer detaches from the surface to form a floating current whose dynamics are controlled by the viscous stresses due to longitudinal extension. We describe the dynamics of the grounded and floating components using distinct thin-layer theories. Separating the grounded and floating regions is the freely moving line of detachment, or grounding line, whose evolution we model by balancing the horizontal forces between the two regions. Using numerical and asymptotic analysis, we calculate the evolution of the system from a self-similar form at early times towards a steady state at late times. We use our solutions to illustrate how three-dimensional stresses within marine ice sheets, such as that of West Antarctica, can lead to stabilization of the grounding line. To assess the validity of the assumptions underlying our model, we compare its predictions with data from a series of laboratory experiments.

Suppression of the von Kármán vortex street behind a circular cylinder by a travelling wave generated by a flexible surface

2007 ◽  
Vol 574 ◽  
pp. 365-391 ◽  
Author(s):  
CHUI-JIE WU ◽  
LIANG WANG ◽  
JIE-ZHI WU
Keyword(s):  
Circular Cylinder ◽  
Pressure Gradient ◽  
Fluid Layer ◽  
Roller Bearing ◽  
Power Saving ◽  
Separated Flow ◽  
Adverse Pressure Gradient ◽  
Travelling Wave ◽  
Cylinder Surface ◽  
Main Stream

An advanced moving-wall control strategy to manage the unsteady separated flow over a circular cylinder is developed. A two-dimensional numerical simulation of the flow over the cylinder at Re=500 based on diameter indicates that, when the downstream half of the cylinder surface is made flexible to form an appropriate travelling transverse wave, a ‘fluid roller bearing’ (FRB) is produced consisting of a row of vortices trapped by each wave trough, which can keep the global flow attached against a strong adverse pressure gradient, eliminating the vortex shedding and reducing the average drag by 85%. Physically, the FRB serves as a sheath to effectively inhibit the momentum–energy exchange between the thin fluid layer adjacent to the wall and the main stream, so that the wall layer is scaled only to the local wavelength and frequency and is independent of the global scales. Therefore, the global adverse pressure gradient on the lee side of the cylinder no longer influences the near-wall flow, and the common root cause of flow separation is removed. The input power for actuating the flexible wall is found to be 94% of the power saving due to drag reduction.

A Micro-Scale Swimmer Propelled by Traveling Surface Waves

2011 ◽  
Author(s):  
Izhak Bucher ◽  
Eyal Setter
Keyword(s):  
Travelling Wave ◽  
Superior Performance ◽  
Small Scale ◽  
Micro Scale ◽  
Viscous Forces ◽  
Macro Scale ◽  
Robotic Devices ◽  
Compact Design ◽  
Micro Organisms ◽  
Efficient Power

Micro-scale slender swimmers are frequently encountered in nature and recently in micro-robotic applications. The swimming mechanism examined in this article is based on small transverse axi-symmetrical travelling wave deformations of a cylindrical long shell. In very small scale, inertia forces become negligible and viscous forces dominate most propulsion mechanisms being used by micro-organisms and robotic devices. The present paper proposes a compact design principle that provides efficient power to propel and maneuver a micro-scale device. Shown in this paper is a numerical analysis which couples the MEMS structure to the surrounding fluid. Analytical results compare the proposed mechanism to commonly found tail (flagella) driven devices, and a parametric comparison is shown suggesting it has superior performance. Numerical studies are preformed to verify the analytical model. Finally, a macro-scale demonstrator swimming in an environment with similar Reynolds numbers to the ones found in small scale is shown and its behavior in the laboratory is compared to the theory.

The turbulence structure of the annular non-swirling flow past an axisymmetric poppet valve

1998 ◽  
Vol 212 (6) ◽  
pp. 455-471 ◽  
Author(s):  
S Nadarajah ◽  
S Balabani ◽  
M J Tindal ◽  
M Yianneskis
Keyword(s):  
Kinetic Energy ◽  
Swirling Flow ◽  
Laser Doppler Anemometry ◽  
Turbulence Kinetic Energy ◽  
Shear Stresses ◽  
Turbulence Structure ◽  
Reynolds Stresses ◽  
Length Scales ◽  
Gaussian Form ◽  
Poppet Valve

This paper describes an experimental investigation of the non-swirling flow through an axisymmetric port and poppet valve assembly under steady flow conditions using laser Doppler anemometry. The three velocity components and the associated Reynolds stresses were measured by ensemble-averaged techniques and the turbulence kinetic energy and its production rate were determined. Time-resolved measurements were also taken in order to determine turbulence time and length scales and the dissipation rate of the turbulence kinetic energy. The Reynolds number, based on the minimum cross-sectional area of the port, was 25000. The flow is characterized by an annular jet which forms two vortices, one on either side of the jet. A jet flapping instability is also evident since the skewness and kurtosis of the velocity probability distribution function depart from the Gaussian form. This instability causes an intermittent mixing between eddies in the jet region and the vortices which introduces a non-turbulent contribution to the measured quantities. The production rates of the turbulence kinetic energy were found to be negative in some regions of the flow, indicating counter-gradient transport of momentum by turbulence; according to the coherent structures approach, the distribution of the Reynolds shear stresses and the length scales in these regions imply possible changes in the orientation of eddies.

Transition in Homogeneously Heated Inclined Plane Parallel Shear Flows

2003 ◽  
Vol 125 (5) ◽  
pp. 795-803 ◽  
Author(s):  
S. Generalis ◽  
M. Nagata
Keyword(s):  
Shear Flows ◽  
Numerical Study ◽  
Fluid Layer ◽  
Travelling Wave ◽  
Inclined Plane ◽  
Vertical Orientation ◽  
Plane Parallel ◽  
Wide Range ◽  
Parallel Shear Flows ◽  
Roll Type

The transition of internally heated inclined plane parallel shear flows is examined numerically for the case of finite values of the Prandtl number Pr. We show that as the strength of the homogeneously distributed heat source is increased the basic flow loses stability to two-dimensional perturbations of the transverse roll type in a Hopf bifurcation for the vertical orientation of the fluid layer, whereas perturbations of the longitudinal roll type are most dangerous for a wide range of the value of the angle of inclination. In the case of the horizontal inclination transverse roll and longitudinal roll perturbations share the responsibility for the prime instability. Following the linear stability analysis for the general inclination of the fluid layer our attention is focused on a numerical study of the finite amplitude secondary travelling-wave solutions (TW) that develop from the perturbations of the transverse roll type for the vertical inclination of the fluid layer. The stability of the secondary TW against three-dimensional perturbations is also examined and our study shows that for Pr=0.71 the secondary instability sets in as a quasi-periodic mode, while for Pr=7 it is phase-locked to the secondary TW. The present study complements and extends the recent study by Nagata and Generalis (2002) in the case of vertical inclination for Pr=0.

The structure of the turbulent boundary layer

1951 ◽  
Vol 47 (2) ◽  
pp. 375-395 ◽  
Author(s):  
A. A. Townsend
Keyword(s):  
Boundary Layer ◽  
Outer Part ◽  
Turbulent Energy ◽  
Turbulent Motion ◽  
Turbulent Shear ◽  
Stream Velocity ◽  
Shear Stresses ◽  
Length Scales ◽  
Displacement Thickness ◽  
Turbulence Length

ABSTRACTThe nature of the turbulent motion in a boundary layer with zero longitudinal pressure gradient has been investigated with the techniques of hot-wire anemometry which have been developed for the study of shear flow in wakes. Measurements have been made of the intensities of the turbulent velocity components, the turbulent shear stresses, the rates of transport of turbulent energy by diffusive movements, the intensities and flattening factors of the down-stream spatial derivatives of the three velocity components, and spectra of the down-stream component of the velocity fluctuation, at traverses through the boundary layer at three stations where the Reynolds numbers (based on the displacement thickness and free stream velocity) were respectively 3630, 4360 and 5080. Over the range of measurement, which did not include the laminar sublayer, the turbulent motion was similar at all three stations, and could be described in terms of universal functions. By considering the turbulent energy balance, it is shown that, except in the outer part of the layer where the turbulence resembles strongly the turbulence in a wake, there is a strong flow of energy directed toward the wall and transported by the action of turbulent pressure gradients. It is concluded that, most probably in contact with the laminar sublayer, there must be a ‘dissipative layer’ within which most of the turbulent energy dissipation takes place, and that the bulk of the eddies are, in a sense, attached to the wall and have very high rates of shear in that region. In agreement with this view of the structure of the turbulence, length scales derived from the apparent eddy viscosity and the local turbulent intensity are found to be comparable with distance from the wall. Length scales in the direction of the mean stream are much larger, and it is believed that the typical eddy is very elongated in this direction, and has its vorticity directed roughly parallel to the direction of maximum positive mean rate of strain.

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