scholarly journals Turbulence Measurements in Pipe Flow With Drag Reducing Polymer Additives

2016 ◽  
Author(s):  
L. Marylin Pumisacho ◽  
Luis Fernando A. Azevedo
Keyword(s):  
Reynolds Number ◽  
Pipe Flow ◽  
Velocity Fields ◽  
Instantaneous Velocity ◽  
Shear Stresses ◽  
Normal Velocity ◽  
Reynolds Stresses ◽  
Velocity Fluctuations ◽  
Turbulent Reynolds Number ◽  
Viscous Shear

Pressure drop and instantaneous velocity fields were measured for fully developed turbulent pipe flow of water and a solution of water and long chain polymer at low concentration. Two-dimensional Particle Image Velocimetry technique — PIV, coupled with a particle tracking technique was employed to yield velocity fields with high spatial resolution. Turbulence statistics were obtained from a series of approximately 2500 instantaneous velocity fields measured for each flow configuration characterized by the turbulent Reynolds number and the polymer concentration. Tests were conducted for a turbulent Reynolds number range from Reτ≈1764 to Reτ≈3154, and for 20 wppm of Superfloc A110 polymer in water. Time-averaged, rms velocity fluctuations and turbulent shear stresses profiles were measured. Drag reductions of the order of 50% were measured. Changes in the axial and wall-normal velocity fluctuations were measured and linked to the presence of the polymer. Reynolds stresses were also shown to decrease in the buffer layer of polymer solution flows as a result of a decrease in the correlation of axial and wall normal fluctuations. A deficit of the viscous shear stress and Reynolds stresses in relation to the total stress was measured close to the wall and attributed to the polymer stresses exerted on the fluid. All the results obtained were in agreement with the available literature, which serve to validate the procedures and test section employed in the experiments.

scholarly journals Turbulence, entrainment and low-order description of a transitional variable-density jet

2017 ◽  
Vol 836 ◽  
pp. 1009-1049 ◽  
Author(s):  
B. Viggiano ◽  
T. Dib ◽  
N. Ali ◽  
L. G. Mastin ◽  
R. B. Cal ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Turbulent Jets ◽  
Reynolds Numbers ◽  
Variable Density ◽  
Quadrant Analysis ◽  
Shear Stresses ◽  
Reynolds Stresses ◽  
Buoyant Jet ◽  
Entrainment Ratio ◽  
Turbulent Reynolds Number

Geophysical flows occur over a large range of scales, with Reynolds numbers and Richardson numbers varying over several orders of magnitude. For this study, jets of different densities were ejected vertically into a large ambient region, considering conditions relevant to some geophysical phenomena. Using particle image velocimetry, the velocity fields were measured for three different gases exhausting into air – specifically helium, air and argon. Measurements focused on both the jet core and the entrained ambient. Experiments considered relatively low Reynolds numbers from approximately 1500 to 10 000 with Richardson numbers near 0.001 in magnitude. These included a variety of flow responses, notably a nearly laminar jet, turbulent jets and a transitioning jet in between. Several features were studied, including the jet development, the local entrainment ratio, the turbulent Reynolds stresses and the eddy strength. Compared to a fully turbulent jet, the transitioning jet showed up to 50 % higher local entrainment and more significant turbulent fluctuations. For this condition, the eddies were non-axisymmetric and larger than the exit radius. For turbulent jets, the eddies were initially smaller and axisymmetric while growing with the shear layer. At lower turbulent Reynolds number, the turbulent stresses were more than 50 % higher than at higher turbulent Reynolds number. In either case, the low-density jet developed faster than a comparable non-buoyant jet. Quadrant analysis and proper orthogonal decomposition were also utilized for insight into the entrainment of the jet, as well as to assess the energy distribution with respect to the number of eigenmodes. Reynolds shear stresses were dominant in Q1 and Q3 and exhibited negligible contributions from the remaining two quadrants. Both analysis techniques showed that the development of stresses downstream was dependent on the Reynolds number while the spanwise location of the stresses depended on the Richardson number.

Turbulent structure in free-surface jet flows

1995 ◽  
Vol 291 ◽  
pp. 223-261 ◽  
Author(s):  
D. T. Walker ◽  
C.-Y. Chen ◽  
W. W. Willmarth
Keyword(s):  
Reynolds Number ◽  
Free Surface ◽  
Froude Number ◽  
Tangential Velocity ◽  
Rate Of Change ◽  
Normal Velocity ◽  
Reynolds Stresses ◽  
Velocity Fluctuations ◽  
Surface Normal ◽  
Surface Disturbances

Results of an experimental study of the interaction of a turbulent jet with a free surface when the jet issues parallel to the free surface are presented. Three different jets, with different exit velocities and jet-exit diameters, all located two jet-exit diameters below the free surface were studied. At this depth the jet flow, in each case, is fully turbulent before significant interaction with the free surface occurs. The effects of the Froude number (Fr) and the Reynolds number (Re) were investigated by varying the jet-exit velocity and jet-exit diameter. Froude-number effects were identified by increasing the Froude number from Fr = 1 to 8 at Re = 12700. Reynolds-number effects were identified by increasing the Reynolds number from Re = 12700 to 102000 at Fr = 1. Qualitative features of the subsurface flow and free-surface disturbances were examined using flow visualization. Measurements of all six Reynolds stresses and the three mean velocity components were obtained in two planes 16 and 32 jet diameters downstream using a three-component laser velocimeter. For all the jets, the interaction of vorticity tangential to the surface with its ‘image’ above the surface contributes to an outward flow near the free surface. This interaction is also shown to be directly related to the observed decrease in the surface-normal velocity fluctuations and the corresponding increase in the tangential velocity fluctuations near the free surface. At high Froude number, the larger surface disturbances diminish the interaction of the tangential vorticity with its image, resulting in a smaller outward flow and less energy transfer from the surface-normal to tangential velocity fluctuations near the surface. Energy is transferred instead to free-surface disturbances (waves) with the result that the turbulence kinetic energy is 20% lower and the Reynolds stresses are reduced. At high Reynolds number, the rate of evolution of the interaction of the jet with the free surface was reduced as shown by comparison of the rate of change with distance downstream of the local Reynolds and Froude numbers. In addition, the decay of tangential vorticity near the surface is slower than for low Reynolds number so that vortex filaments have time to undergo multiple reconnections to the free surface before they eventually decay.

scholarly journals Sound radiation in turbulent channel flows

2003 ◽  
Vol 475 ◽  
pp. 269-302 ◽  
Author(s):  
ZHIWEI HU ◽  
CHRISTOPHER L. MORFEY ◽  
NEIL D. SANDHAM
Keyword(s):  
Mach Number ◽  
Sound Radiation ◽  
Fourth Power ◽  
Shear Stresses ◽  
Far Field ◽  
Good Resolution ◽  
Reynolds Stresses ◽  
Rigid Boundary ◽  
Frequency Spectra ◽  
Viscous Shear

Lighthill’s acoustic analogy is formulated for turbulent channel flow with pressure as the acoustic variable, and integrated over the channel width to produce a two-dimensional inhomogeneous wave equation. The equivalent sources consist of a dipole distribution related to the sum of the viscous shear stresses on the two walls, together with monopole and quadrupole distributions related to the unsteady turbulent dissipation and Reynolds stresses respectively. Using a rigid-boundary Green function, an expression is found for the power spectrum of the far-field pressure radiated per unit channel area. Direct numerical simulations (DNS) of turbulent plane Poiseuille and Couette flow have been performed in large computational domains in order to obtain good resolution of the low-wavenumber source behaviour. Analysis of the DNS databases for all sound radiation sources shows that their wavenumber–frequency spectra have non-zero limits at low wavenumber. The sound power per unit channel area radiated by the dipole distribution is proportional to Mach number squared, while the monopole and quadrupole contributions are proportional to the fourth power of Mach number. Below a particular Mach number determined by the frequency and radiation direction, the dipole radiation due to the wall shear stress dominates the far field. The quadrupole takes over at Mach numbers above about 0.1, while the monopole is always the smallest term. The resultant acoustic field at any point in the channel consists of a statistically diffuse assembly of plane waves, with spectrum limited by damping to a value that is independent of Mach number in the low-M limit.

Prediction and investigation of the turbulent flow over a rotating disk

2000 ◽  
Vol 418 ◽  
pp. 231-264 ◽  
Author(s):  
XIAOHUA WU ◽  
KYLE D. SQUIRES
Keyword(s):  
Boundary Layer ◽  
Rotating Disk ◽  
Shear Stresses ◽  
Normal Velocity ◽  
Streamwise Vortices ◽  
Streamwise Vorticity ◽  
Velocity Fluctuations ◽  
Buffer Region ◽  
The Mean ◽  
Good Agreement

Large-eddy simulation (LES) has been used to predict the statistically three-dimensional turbulent boundary layer (3DTBL) over a rotating disk. LES predictions for six parameter cases were compared to the experimental measurements of Littell & Eaton (1994), obtained at a momentum thickness Reynolds number of 2660. A signal-decomposition scheme was developed by modifying the method of Spalart (1988) to prescribe time-dependent boundary conditions along the radial direction, entrainment towards the disk surface was prescribed by satisfying global mass conservation. Predictions of the mean velocities and r.m.s. fluctuations are in good agreement with data, with the largest discrepancy occurring in the prediction of the wall-normal intensities. The primary and two secondary shear stresses are also in good agreement with the measurements and one-dimensional energy spectra of the velocity fluctuations agree well with established laws, i.e. a −1 slope in the buffer region and −5/3 slope near the edge of the boundary layer.Conditionally averaged velocities provide new evidence in support of the structural model of Littell & Eaton (1994) concerning the interaction of mean-flow three-dimensionality and shear-stress producing structures. Inside the buffer region under strong ejections, the conditionally averaged crossflow (radial) velocity is larger than the unconditioned mean, and the profile conditioned on strong sweeps is smaller than the mean. This is consistent with the notion that streamwise vortices having the same sign as the mean streamwise vorticity, and beneath the peak crossflow location, are mostly responsible for strong sweep events; streamwise vortices with opposite sign as the mean streamwise vorticity promote strong ejections. Comparison of two-point spatial correlations with previous measurements in two-dimensional turbulent boundary layers (2DTBLs) indicates interesting structural similarities, e.g. the correlation of wall pressure and surface-normal velocity fluctuations is an odd function of streamwise separation, being positive downstream and negative upstream. These similarities offer quantitative indirect support to the hypothesis advanced by Littell & Eaton (1994) and Johnston & Flack (1996) that structural models describing 2DTBLs may be employed as a baseline in (equilibrium) 3DTBL structural studies.

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.

scholarly journals Flow instabilities in a graft anastomosis: A study of the instantaneous velocity fields

2001 ◽  
Vol 215 (6) ◽  
pp. 579-587 ◽  
Author(s):  
C J Bates ◽  
D M O'Doherty ◽  
D Williams
Keyword(s):  
Intimal Hyperplasia ◽  
Bypass Graft ◽  
Reynolds Numbers ◽  
Velocity Fields ◽  
Instantaneous Velocity ◽  
Working Fluid ◽  
Shear Stresses ◽  
Complex Flow ◽  
Image Velocimetry ◽  
Arterial Bypass Graft

The major cause of arterial bypass graft failure is intimal hyperplasia. Fluctuating wall shear stresses in the graft, which are associated with disturbed flow, are believed to be important factors in the development and localization of intimal hyperplasia. This study, based upon water as the working fluid, has investigated the flow structure inside a 30° Y-junction with different fillet radii at the intersection between the graft and the host artery at various Reynolds numbers and distal outlet segment (DOS) to proximal outlet segment (POS) flow ratios. The structure of the flow has been investigated experimentally using particle image velocimetry (PIV). The two-dimensional instantaneous velocity fields confirm the existence of a very complex flow, especially in the toe and heel regions for the different fillet radii and clearly identify features such as sinks, sources, vortices and strong time dependency.

Reynolds Number Dependence of Zero Pressure Gradient Turbulent Boundary Layers Including Third-Order Moments and Spatial Correlations

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Ralph J. Volino
Keyword(s):  
Reynolds Number ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Field Measurements ◽  
Turbulent Boundary Layers ◽  
Quadrant Analysis ◽  
Shear Stresses ◽  
Reynolds Stresses ◽  
Spatial Correlations ◽  
Mean Velocity

Abstract Measurements were made in zero pressure gradient turbulent boundary layers on a smooth wall, at momentum thickness Reynolds numbers, ranging from 800 to 6340. The experiments were conducted in a recirculating water tunnel. Two-component velocity profiles were acquired using laser Doppler velocimetry at five streamwise stations and three different freestream velocities. Velocity field measurements were acquired using particle image velocimetry in streamwise-wall normal and streamwise–spanwise planes. Profiles of mean velocity and turbulence statistics including the Reynolds normal and shear stresses, and triple products of the velocity fluctuations are presented in both inner and outer coordinates. Variations in the profiles at representative distances from the wall are presented and quantified as functions of Reynolds number. The triple products are explained in terms of transport of Reynolds stresses though motions associated with quadrant analysis, and variation with Reynolds number is consistent with that of Reynolds stresses. The structure of turbulence was considered through two-point correlations of the fluctuations in velocity fields. In general, the shape and inclination angles of the structures did not change with Reynolds number, but some streamwise and spanwise growth was observed as Reynolds number increased.

REYNOLDS STRESSES IN CONFINED VORTEX FLOWS

1999 ◽  
Vol 23 (2) ◽  
pp. 287-305
Author(s):  
L. Yan ◽  
S. Lin ◽  
G.H. Vatistas
Keyword(s):  
Reynolds Number ◽  
Vortex Flow ◽  
Laser Doppler Anemometry ◽  
Vortex Chamber ◽  
Shear Stresses ◽  
Vortex Flows ◽  
Reynolds Stresses ◽  
Unknown Parameters ◽  
Contraction Ratio ◽  
Energy Equations

Reynolds stresses in confined vortex flows have been studied analytically and experimentally. Equations for the Reynolds shear stresses are derived based on the kinetic energy equations and experimental observations. The Reynolds shear stresses are obtained by solving the equations analytically. The unknown parameters appearing in the analytical solutions are determined from experimental data. The Reynolds normal stresses are obtained directly from the experiments which are performed by means of Laser Doppler Anemometry (LDA). The effects of the contraction ratio and the inlet Reynolds number on the Reynolds stresses in the vortex flow from the main section to the exit section of the vortex chamber are analyzed. It is found that the contraction ratio affects the behaviour of the Reynolds stresses, and that a higher inlet Reynolds number results in a higher level of the Reynolds stresses.

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