On transition of the pulsatile pipe flow

1986 ◽  
Vol 170 ◽  
pp. 169-197 ◽  
Author(s):  
J. C. Stettler ◽  
A. K. M. Fazle Hussain
Keyword(s):  
Steady Flow ◽  
Pipe Flow ◽  
Three Dimensional ◽  
Building Blocks ◽  
Rate Of Change ◽  
Turbulent Pipe Flow ◽  
Dimensional Parameter ◽  
Pipe Length ◽  
The Mean ◽  
The Stability

Transition in a pipe flow with a superimposed sinusoidal modulation has been studied in a straight circular water pipe using laser-Doppler anemometer (LDA) techniques. This study has determined the stability–transition boundary in the three-dimensional parameter space defined by the mean and modulation Reynolds numbers Rem, Remω and the frequency parameter λ. Furthermore, it documents the mean passage frequency Fp of ‘turbulent plugs’ as functions of Rem’ Remω and λ. This study also delineates the conditions when plugs occur randomly in time (as in the steady flow) or phase-locked with the excitation. The periodic flow requires a new definition of the transitional Reynolds number Rer, identified on the basis of the rate of change of Fp with Rem. The extent of increase or decrease in Rer from the corresponding steady flow value depends on λ and Remω. At any Rem and Remω, maximum stabilization occurs at λ ≈ 5. With increasing Remω, the ‘stabilization bandwidth’ of modulation frequencies increases and then abruptly decreases after levelling off. The maximum stabilization bandwidth depends strongly on Rem, decreasing with increasing Rem. Previously reported observations of turbulence during deceleration, followed by a relaminarization during acceleration, can be explained in terms of a new phenomenon: namely, periodic modulation produces longitudinally periodic cells of turbulent fluid ‘plugs’ which differ in structural details from ‘puffs’ or ‘slugs’ in steady transitional pipe flows and are called patches. The length of a patch could be increased continuously from zero to the entire pipe length by increasing Rem. This tends to question the concept that all turbulent plugs (and even the fully-turbulent pipe flow) consists of many identical elementary plugs as basic ‘building blocks’.

scholarly journals Experimental and theoretical progress in pipe flow transition

2008 ◽  
Vol 366 (1876) ◽  
pp. 2671-2684 ◽  
Author(s):  
A.P Willis ◽  
J Peixinho ◽  
R.R Kerswell ◽  
T Mullin
Keyword(s):  
Pipe Flow ◽  
Quantitative Agreement ◽  
Travelling Wave ◽  
Turbulent Pipe Flow ◽  
Transition To Turbulence ◽  
Reynolds Number Flow ◽  
Threshold Amplitude ◽  
Number Flow ◽  
The Stability ◽  
Laminar State

There have been many investigations of the stability of Hagen–Poiseuille flow in the 125 years since Osborne Reynolds' famous experiments on the transition to turbulence in a pipe, and yet the pipe problem remains the focus of attention of much research. Here, we discuss recent results from experimental and numerical investigations obtained in this new century. Progress has been made on three fundamental issues: the threshold amplitude of disturbances required to trigger a transition to turbulence from the laminar state; the threshold Reynolds number flow below which a disturbance decays from turbulence to the laminar state, with quantitative agreement between experimental and numerical results; and understanding the relevance of recently discovered families of unstable travelling wave solutions to transitional and turbulent pipe flow.

Estimating the value of von Kármán’s constant in turbulent pipe flow

2014 ◽  
Vol 749 ◽  
pp. 79-98 ◽  
Author(s):  
S. C. C. Bailey ◽  
M. Vallikivi ◽  
M. Hultmark ◽  
A. J. Smits
Keyword(s):  
Pipe Flow ◽  
Turbulent Pipe Flow ◽  
Data Sets ◽  
Mean Velocity ◽  
Princeton University ◽  
Best Estimate ◽  
Data Points ◽  
Smooth Pipe ◽  
The Mean ◽  
Hot Wires

AbstractFive separate data sets on the mean velocity distributions in the Princeton University/ONR Superpipe are used to establish the best estimate for the value of von Kármán’s constant for the flow in a fully developed, hydraulically smooth pipe. The profiles were taken using Pitot tubes, conventional hot wires and nanoscale thermal anemometry probes. The value of the constant was found to vary significantly due to measurement uncertainties in the mean velocity, friction velocity and the wall distance, and the number of data points included in the analysis. The best estimate for the von Kármán constant in turbulent pipe flow is found to be $0.40 \pm 0.02$. A more precise estimate will require improved instrumentation.

On the stability of parallel flows with parallel magnetic fields

1966 ◽  
Vol 293 (1434) ◽  
pp. 342-358 ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Parallel Magnetic Field ◽  
Parallel Flows ◽  
The Mean ◽  
The Stability ◽  
The Magnetic Field ◽  
Parallel Magnetic Fields

The first part of the paper is a physical discussion of the way in which a magnetic field affects the stability of a fluid in motion. Particular emphasis is given to how the magnetic field affects the interaction of the disturbance with the mean motion. The second part is an analysis of the stability of plane parallel flows of fluids with finite viscosity and conductivity under the action of uniform parallel magnetic fields. We show that, in general, three-dimensional disturbances are the most unstable, thus disagreeing with the conclusion of Michael (1953) and Stuart (1954). We show how results obtained for two-dimensional disturbances can be used to calculate the most unstable three-dimensional disturbances and thence we prove that a parallel magnetic field can never completely stabilize a parallel flow.

scholarly journals Ethyl 2-(2-methyl-4-nitro-1H-imidazol-1-yl)acetate

IUCrData ◽  
2016 ◽  
Vol 1 (4) ◽  
Author(s):  
Yassine Hakmaoui ◽  
El Mostapha Rakib ◽  
Souad Mojahidi ◽  
Mohamed Saadi ◽  
Lahcen El Ammari
Keyword(s):  
Hydrogen Bonds ◽  
Title Compound ◽  
Crystal Packing ◽  
Three Dimensional ◽  
Imidazole Ring ◽  
Compound C ◽  
Dimensional Network ◽  
The Mean ◽  
Packing Arrangement ◽  
The Stability

In the title compound, C8H11N3O4, the imidazole ring and the nitro group are nearly coplanar, with the largest deviation from the mean plane being 0.119 (2) Å. The mean plane through the acetate group is approximately perpendicular to the imidazole ring, subtending a dihedral angle of 75.71 (13)°. In the crystal, molecules are linked by weak C—H...O and very weak C—H...N hydrogen bonds, forming a three-dimensional network. There is also a weak C—H...π(imidazole) interaction, which contributes to the stability of the crystal packing arrangement.

Flow Past a Permeable Manipulator Ring Placed in a Turbulent Pipe Flow

2011 ◽  
Author(s):  
Koji Utsunomiya ◽  
Suketsugu Nakanishi ◽  
Hideo Osaka
Keyword(s):  
Turbulent Flow ◽  
Shear Layer ◽  
Pipe Flow ◽  
Area Ratio ◽  
Turbulent Pipe Flow ◽  
Wall Region ◽  
Open Area ◽  
Mean Flow ◽  
Flow Past ◽  
The Mean

Turbulent pipe flow past a ring-type permeable manipulator was investigated by measuring the mean flow and turbulent flow fields. The permeable manipulator ring had a rectangular cross section and a height 0.14 times the pipe radius. The experiments were performed under four conditions of the open area ratio β of the permeable ring (β = 0.1, 0.2, 0.3 and 0.4) for Reynolds number of 6.2×104. The results indicate that as the open-area ratio increased, the separated shear layer arising from the permeable ring top became weaker and the pressure loss was reduced by increasing fluid flow through the permeable ring. When β was less than 0.2, the velocity gradient was steeper over the permeable ring and in the shear layer near the reattachment region. When β was greater than 0.3, the width of the shear layer showed a relatively large augmentation and the back pressure in the separating region increases. Further, the response of the turbulent flow field to the permeable ring was delayed compared with that of the mean velocity field, and these differences increased with β. The turbulence intensities and Reynolds shear stress profiles near the reattachment point increased near the wall region as β increased, while those peak values that were taken at the locus of the manipulator ring height decreased as β increased.

Steady Flow Approximations in Three-Dimensional Ship Motion Calculation

2007 ◽  
Vol 51 (03) ◽  
pp. 229-249 ◽  
Author(s):  
Booki Kim ◽  
Yung-Sup Shin
Keyword(s):  
Green Function ◽  
Wave Field ◽  
Steady Flow ◽  
Three Dimensional ◽  
Wave Flow ◽  
Steady Wave ◽  
Flow Models ◽  
Submerged Sphere ◽  
The Mean ◽  
Green Function Approach

When a ship advances at constant speed in waves, the steady flow interacts with the unsteady wave field generated by the ship's motion. The interaction between the steady flow and the unsteady wave field appears in so-called mj terms. The three different steady flow models, that is, free stream, double body flow, and steady wave flow, are considered for the realization of the mj terms. For completeness in a linear sense, the steady flow contributions are retained in a consistent manner in the expressions for the hydrodynamic and restoring forces, which can be derived from the integration of the linearized pressure over the mean wetted part of the hull surface. The steady trim and sinkage are also considered important in determining the mean wetted position. The numerical results are obtained using a three-dimensional panel method based on a translating and pulsating Green function approach. An efficient numerical method is applied for the accurate evaluation of the mj terms without deriving the second derivatives of the Green function. Numerical calculations have been made for a submerged sphere and a Wigley hull. It is found that the steady flow has strong influence on added masses and damping forces in heave and pitch at relatively low encounter frequencies, while its effect is not observed as significant in wave exciting forces. The importance of the steady flow effect is also pronounced in the peak values of heave and pitch motion responses. In comparison with semiana-lytical and experimental results, the double body and steady wave flows are found to be the proper choices for the steady flow approximation.

A theory of particle deposition in turbulent pipe flow

1997 ◽  
Vol 340 ◽  
pp. 129-159 ◽  
Author(s):  
JOHN YOUNG ◽  
ANGUS LEEMING
Keyword(s):  
Pipe Flow ◽  
Particle Deposition ◽  
Particle Concentration ◽  
Dynamic Behaviour ◽  
Three Dimensional ◽  
Turbulent Pipe Flow ◽  
Particle Dynamic ◽  
Free Flight ◽  
Small Correction ◽  
Saffman Lift Force

The paper describes a theory of particle deposition based formally on the conservation equations of particle mass and momentum. These equations are formulated in an Eulerian coordinate system and are then Reynolds averaged, a procedure which generates a number of turbulence correlations, two of which are of prime importance. One represents ‘turbulent diffusion’ and the other ‘turbophoresis’, a convective drift of particles down gradients of mean-square fluctuating velocity. Turbophoresis is not a small correction; it dominates the particle dynamic behaviour in the diffusion-impaction and inertia-moderated regimes.Adopting a simple model for the turbophoretic force, the theory is used to calculate deposition from fully developed turbulent pipe flow. Agreement with experimental measurements is good. It is found that the Saffman lift force plays an important role in the inertia-moderated regime but that the effect of gravity on deposition from vertical flows is negligible. The model also predicts an increase in particle concentration close to the wall in the diffusion-impaction regime, a result which is partially corroborated by an independent ‘direct numerical simulation’ study.The new deposition theory represents a considerable advance in physical understanding over previous free-flight theories. It also offers many avenues for future development, particularly in the simultaneous calculation of laminar (pure inertial) and turbulent particle transport in more complex two- and three-dimensional geometries.

Nonasymptotic behavior of developing turbulent pipe flow

1976 ◽  
Vol 54 (3) ◽  
pp. 268-278 ◽  
Author(s):  
J. K. Reichert ◽  
R. S. Azad
Keyword(s):  
Reynolds Number ◽  
Pipe Flow ◽  
Reynolds Numbers ◽  
Peak Position ◽  
Turbulent Pipe Flow ◽  
Shear Stresses ◽  
Mean Velocity ◽  
Inlet Region ◽  
The Mean ◽  
Hot Film

Detailed measurements of mean velocity U profiles, in the inlet 70 diameters of a pipe, show that the development of turbulent pipe flow is nonasymptotic. Experiments were done at seven Reynolds numbers in the range 56 000–15 3000. Contours of U and V fields are presented for two representative Reynolds numbers. A U component peak exceeding the fully developed values has been found to occur along the pipe centerline. The Reynolds number behavior of the peak position has been determined. Hot film measurements of the mean wall shear stresses in the inlet region also show a nonasymptotic development consistent with the mean velocity results.

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