Critical Reynolds Number in Constant-Acceleration Pipe Flow From an Initial Steady Laminar State

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Charles W. Knisely ◽  
Kazuyoshi Nishihara ◽  
Manabu Iguchi
Keyword(s):  
Reynolds Number ◽  
Flow Visualization ◽  
Pipe Flow ◽  
Laser Doppler Velocimetry ◽  
Critical Reynolds Number ◽  
Transition To Turbulence ◽  
Doppler Velocimetry ◽  
Constant Acceleration ◽  
Laminar State ◽  
Steady Laminar

The transition to turbulence in a constant-acceleration pipe flow from an initial laminar state was investigated in a custom-made apparatus permitting visual access to the water flow in the pipe. The apparatus allowed both laser Doppler velocimetry measurements and flow visualization using a tracer. The experiment was carried out by accelerating the flow from a steady laminar state to a steady turbulent state. The relation between the critical Reynolds number for transition to turbulence and the acceleration was found to be similar to that in a constant-acceleration pipe flow started from rest. In addition, with increased acceleration, the turbulent transition was found to be delayed to higher Reynolds numbers using flow visualization with simultaneous laser Doppler velocimetry measurements.

Effect of Initial Constant Acceleration on the Transition to Turbulence in Transient Circular Pipe Flow

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
Manabu Iguchi ◽  
Kazuyoshi Nishihara ◽  
Yusuke Nakahata ◽  
Charles W. Knisely
Keyword(s):  
Reynolds Number ◽  
Pipe Flow ◽  
Time Lag ◽  
Transition To Turbulence ◽  
Circular Pipe ◽  
Constant Acceleration ◽  
Mean Velocity ◽  
Cross Sectional ◽  
Circular Pipe Flow ◽  
The Cross

Experimental investigation is carried out on the transition to turbulence in a transient circular pipe flow. The flow is accelerated from rest at a constant acceleration until its cross-sectional mean velocity reaches a constant value. Accordingly, the history of the flow thus generated consists of the initial stage of constant acceleration and the following stage of constant cross-sectional mean velocity. The final Reynolds number based on the constant cross-sectional mean velocity and the pipe diameter is chosen to be much greater than the transition Reynolds number of a steady pipe flow of about 3000. The transition to turbulence is judged from the output signal of the axial velocity component and its root-mean-square value measured with a hot-wire anemometer. A turbulent slug appears after the cross-sectional mean velocity of the flow reaches the predetermined constant value under every experimental condition. Turbulence production therefore is suppressed, while the flow is accelerated. The time lag for the appearance of the turbulent slug after the cross-sectional mean velocity of the flow reaches the constant value decreases with an increase in the constant acceleration value. An empirical equation is proposed for estimating the time lag. The propagation velocity of the leading edge of the turbulent slug is independent of the constant acceleration value under the present experimental conditions.

scholarly journals Subcritical versus supercritical transition to turbulence in curved pipes

2015 ◽  
Vol 770 ◽  
Author(s):  
J. Kühnen ◽  
P. Braunshier ◽  
M. Schwegel ◽  
H. C. Kuhlmann ◽  
B. Hof
Keyword(s):  
Reynolds Number ◽  
Hopf Bifurcation ◽  
Laser Doppler Velocimetry ◽  
Basic Flow ◽  
Transition To Turbulence ◽  
Doppler Velocimetry ◽  
Minimum Threshold ◽  
Curved Pipes ◽  
Friction Factors ◽  
Helical Pipe

Transition to turbulence in straight pipes occurs in spite of the linear stability of the laminar Hagen–Poiseuille flow if both the amplitude of flow perturbations and the Reynolds number $\mathit{Re}$ exceed a minimum threshold (subcritical transition). As the pipe curvature increases, centrifugal effects become important, modifying the basic flow as well as the most unstable linear modes. If the curvature (tube-to-coiling diameter $d/D$) is sufficiently large, a Hopf bifurcation (supercritical instability) is encountered before turbulence can be excited (subcritical instability). We trace the instability thresholds in the $\mathit{Re}-d/D$ parameter space in the range $0.01\leqslant d/D\leqslant 0.1$ by means of laser-Doppler velocimetry and determine the point where the subcritical and supercritical instabilities meet. Two different experimental set-ups are used: a closed system where the pipe forms an axisymmetric torus and an open system employing a helical pipe. Implications for the measurement of friction factors in curved pipes are discussed.

scholarly journals Experimental investigation of the kinetic energy correction factor in pipe flow

2018 ◽  
Vol 44 ◽  
pp. 00177 ◽  
Author(s):  
Tomasz Janusz Teleszewski
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Kinetic Energy ◽  
Correction Factor ◽  
Pipe Flow ◽  
Laser Doppler Velocimetry ◽  
Experimental Results ◽  
Doppler Velocimetry ◽  
Energy Correction ◽  
Smooth Pipe

In this study, an experimental investigation of the kinetic energy (Coriolis) correction factor in laminar, transitional and turbulent flow in a transparent smooth pipe with a Reynolds number up to 25000 is performed. The velocity profiles are obtained using a laser Doppler velocimetry (LDV). Based on the experimental results obtained for Re < 25000, generalized correlations for the kinetic energy correction factor as a function of the Reynolds number are presented. The results of the research are compared with experimental results reported by other authors. The predicted correlations for the kinetic energy correction factor can be a very useful resource for the hydraulic calculations of fluid through circular ducts.

Symmetric and Asymmetric Turbulent Flows in a Rectangular Duct With a Pair of Ribs

1988 ◽  
Vol 110 (4) ◽  
pp. 373-379 ◽  
Author(s):  
T.-M. Liou ◽  
C.-F. Kao
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Flows ◽  
Laser Doppler Velocimetry ◽  
Boundary Layer Thickness ◽  
Critical Reynolds Number ◽  
Doppler Velocimetry ◽  
Rectangular Duct ◽  
Reattachment Length ◽  
Mean Velocity

Laser-Doppler velocimetry (LDV) measurements are presented of mean velocity and turbulence intensity for turbulent flows past a pair of ribs in a rectangular duct of aspect ratio 2. The Reynolds number based on the duct hydraulic diameter was varied in the range of 2.0 × 103 to 7.6 × 104. The experiments cover ribs with rib height to duct height ratios from 0.13 to 0.33 and with rib width to height ratios from 1 to 10. The critical rib height above which and the critical Reynolds number below which the flow patterns become asymmetric were determined from the results. In addition, the effects of the rib width and boundary layer thickness on the formation and the size of the separation bubbles on the top surface of the ribs as well as on the reattachment length behind the ribs were documented. Furthermore, the degree of turbulence enhancement was compared between the asymmetric and the symmetric flows.

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.

The effect of rigid rotation on the finite-amplitude stability of pipe flow at high Reynolds number

1984 ◽  
Vol 148 ◽  
pp. 193-205 ◽  
Author(s):  
T. R. Akylas ◽  
J.-P. Demurger
Keyword(s):  
Reynolds Number ◽  
Pipe Flow ◽  
High Reynolds Number ◽  
Finite Amplitude ◽  
Linear Instability ◽  
Rigid Rotation ◽  
Transition To Turbulence ◽  
Neutral Stability ◽  
Axisymmetric Mode ◽  
High Reynolds

A theoretical study is made of the stability of pipe flow with superimposed rigid rotation to finite-amplitude disturbances at high Reynolds number. The non-axisymmetric mode that requires the least amount of rotation for linear instability is considered. An amplitude expansion is developed close to the corresponding neutral stability curve; the appropriate Landau constant is calculated. It is demonstrated that the flow exhibits nonlinear subcritical instability, the nonlinear effects being particularly strong owing to the large magnitude of the Landau constant. These findings support the view that a small amount of extraneous rotation could play a significant role in the transition to turbulence of pipe flow.

Fluid Dynamic Characteristics of the Flow Over an Array of Large Roughness Elements

1991 ◽  
Vol 113 (4) ◽  
pp. 367-373 ◽  
Author(s):  
S. V. Garimella ◽  
P. A. Eibeck
Keyword(s):  
Reynolds Number ◽  
Laser Doppler Velocimetry ◽  
Fluid Dynamic ◽  
Water Channel ◽  
Leading Edge ◽  
Channel Height ◽  
Doppler Velocimetry ◽  
Reattachment Length ◽  
Roughness Elements ◽  
Large Roughness

Flow visualization and measurements of velocity and turbulence intensity using laser Doppler velocimetry are used to investigate separation and reattachment processes in the flow over an array of protruding elements mounted on the bottom wall of a rectangular water channel. The concept of an array shear layer is introduced to demarcate the region of influence over which the resistance of the array retards the flow. Flow separation at the leading edge of the elements is documented. The confined or interacting nature of the flow in the cavities between elements is established as a function of element spacing. The reattachment length downstream of the element varies from 4 to 1.5 element heights, decreasing both with an increase in Reynolds number and a decrease in channel height.

Experiments on transition to turbulence in an oscillatory pipe flow

1976 ◽  
Vol 75 (2) ◽  
pp. 193-207 ◽  
Author(s):  
Mikio Hino ◽  
Masaki Sawamoto ◽  
Shuji Takasu
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Pipe Flow ◽  
Stokes Parameter ◽  
Angular Frequency ◽  
Transition To Turbulence ◽  
Mean Velocity ◽  
Cross Sectional ◽  
Velocity Amplitude ◽  
Turbulent Flow Regime

Experiments on transition to turbulence in a purely oscillatory pipe flow were performed for values of the Reynolds number Rδ, defined using the Stokes-layer thickness δ = (2ν/ω)½ and the cross-sectional mean velocity amplitude Û, from 19 to 1530 (or for values of the Reynolds number Re, defined using the pipe diameter d and Û, from 105 to 5830) and for values of the Stokes parameter λ = ½d(ω/2ν)½ (ν = kinematic viscosity and ω = angular frequency) from 1·35 to 6·19. Three types of turbulent flow regime have been detected: weakly turbulent flow, conditionally turbulent flow and fully turbulent flow. Demarcation of the flow regimes is possible on Rλ, λ or Re, λ diagrams. The critical Reynolds number of the first transition decreases as the Stokes parameter increases. In the conditionally turbulent flow, turbulence is generated suddenly in the decelerating phase and the profile of the velocity distribution changes drastically. In the accelerating phase, the flow recovers to laminar. This type of partially turbulent flow persists even at Reynolds numbers as high as Re = 5830 if the value of the Stokes parameter is high.

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