An investigation of possible mechanisms of heterogeneous drag reduction in pipe and channel flows

1993 ◽  
Vol 32 (2) ◽  
pp. 140-149 ◽  
Author(s):  
H. W. Bewersdorff ◽  
A. Gyr ◽  
K. Hoyer ◽  
A. Tsinober
Keyword(s):  
Drag Reduction ◽  
Channel Flows ◽  
Heterogeneous Drag Reduction

Drag reduction and turbulent structure in two-dimensional channel flows

1991 ◽  
Vol 336 (1640) ◽  
pp. 19-34 ◽  
Keyword(s):  
Shear Stress ◽  
Drag Reduction ◽  
Strain Rate ◽  
Reynolds Stress ◽  
Polymer Concentration ◽  
Turbulent Structure ◽  
Channel Flows ◽  
Channel Height ◽  
Normal Velocity ◽  
Two Dimensional

A two-component laser velocimeter has been used to determine the effect of wall strain rate, polymer concentration and channel height upon the drag reduction and turbulent structure in fully developed, low concentration, two-dimensional channel flows. Water flows at equal wall shear stress and with Reynolds numbers from 14430 to 34640 were measured for comparison. Drag reduction levels clearly depended upon wall strain rate, polymer concentration and channel height independently.However, most of the turbulent structure depended only upon the level of drag reduction. The slope of the logarithmic law of the wall increased as drag reduction increased. Similarly, the root-mean-square of the fluctuations in the streamwise velocity increased while the r.m.s. of the fluctuations in the wall-normal velocity decreased with drag reduction. The production of the streamwise normal Reynolds stress and the Reynolds shear stress decreased in the drag-reduced flows. Therefore it appears that the polymer solutions inhibit the transfer of energy from the streamwise to the wall-normal velocity fluctuations. This could occur through inhibiting the newtonian transfer mechanism provided by the pressure-strain correlation. In six drag-reducing flows, the sum of the Reynolds stress and the mean viscous stress was equal to the total shear stress. However, for the combination of highest concentration (5 p.p.m.), smallest channel height (25 mm) and highest wall strain rate (4000 s - 1 ), the sum of the Reynolds and viscous stresses was substantially lower than the total stress indicating the presence of a strong non-newtonian effect. In all drag-reducing flows the correlation coefficient for uv decreased as the axes of principal stress for the Reynolds stress rotated toward the streamwise and wall-normal directions.

scholarly journals Comparison of theory and direct numerical simulations of drag reduction by rodlike polymers in turbulent channel flows

2008 ◽  
Vol 77 (4) ◽  
Author(s):  
Roberto Benzi ◽  
Emily S. C. Ching ◽  
Elisabetta De Angelis ◽  
Itamar Procaccia
Keyword(s):  
Drag Reduction ◽  
Numerical Simulations ◽  
Direct Numerical Simulations ◽  
Channel Flows ◽  
Turbulent Channel Flows ◽  
Rodlike Polymers

A combined PIV/LIF-system for the measurement of heterogeneous drag reduction effects in a pipe-flow

1997 ◽  
Vol 22 (4) ◽  
pp. 292-299 ◽  
Author(s):  
M. Saadeh ◽  
K. Strauss ◽  
T. Schneider
Keyword(s):  
Drag Reduction ◽  
Pipe Flow ◽  
Heterogeneous Drag Reduction

On the maximum drag reduction due to added polymers in Poiseuille flow

2010 ◽  
Vol 659 ◽  
pp. 473-483 ◽  
Author(s):  
JAMES D. WOODCOCK ◽  
JOHN E. SADER ◽  
IVAN MARUSIC
Keyword(s):  
Lower Bound ◽  
Constitutive Equation ◽  
Drag Reduction ◽  
Poiseuille Flow ◽  
Channel Flows ◽  
Water Droplets ◽  
Flowing Liquid ◽  
Maximum Drag Reduction ◽  
Sand Particles

The addition of elastic polymers to turbulent liquids is known to produce significant drag reduction. In this study, we prove that the drag in pipe and channel flows of an unforced laminar fluid constitutes a lower bound for the drag of a fluid containing dilute elastic polymers. Further, the addition of elastic polymers to laminar fluids invariably increases drag. This proof does not rely on the adoption of a particular constitutive equation for the polymer force, and would also be applicable to other similar methods of drag reduction, which are also achieved by the addition of certain particles to a flow. Examples of such methods include the addition of surfactants to a flowing liquid and the presence of sand particles in sandstorms and water droplets in cyclones.

Comparison of superhydrophobic drag reduction between turbulent pipe and channel flows

2017 ◽  
Vol 29 (9) ◽  
pp. 095101 ◽  
Author(s):  
Hyung Jae Im ◽  
Jae Hwa Lee
Keyword(s):  
Drag Reduction ◽  
Channel Flows

Drag Reduction Due to Streamwise Grooves in Turbulent Channel Flow

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
C. T. DeGroot ◽  
C. Wang ◽  
J. M. Floryan
Keyword(s):  
Shear Stress ◽  
Drag Reduction ◽  
Turbulent Channel Flow ◽  
Surface Modifications ◽  
Channel Flows ◽  
Wave Number ◽  
Stress Profile ◽  
Bulk Fluid ◽  
Geometry Model ◽  
Turbulent Channel Flows

Drag reduction in turbulent channel flows has significant practical relevance for energy savings. Various methods have been proposed to reduce turbulent skin friction, including microscale surface modifications such as riblets or superhydrophobic surfaces. More recently, macroscale surface modifications in the form of longitudinal grooves have been shown to reduce drag in laminar channel flows. The purpose of this study is to show that these grooves also reduce drag in turbulent channel flows and to quantify the drag reduction as a function of the groove parameters. Results are obtained using computational fluid dynamics (CFD) simulations with turbulence modeled by the k–ω shear-stress transport (SST) model, which is first validated with direct numerical simulations (DNS). Based on the CFD results, a reduced geometry model is proposed which shows that the approximate drag reduction can be quantified by evaluating the drag reduction of the geometry given by the first Fourier mode of an arbitrary groove geometry. Results are presented to show the drag reducing potential of grooves as a function of Reynolds number as well as groove wave number, amplitude, and shape. The mechanism of drag reduction is discussed, which is found to be due to a rearrangement of the bulk fluid motion into high-velocity streamtubes in the widest portion of the channel opening, resulting in a change in the wall shear stress profile.

Use of particle image velocimetry to study heterogeneous drag reduction

2005 ◽  
Vol 39 (4) ◽  
pp. 637-650 ◽  
Author(s):  
S. Baik ◽  
M. Vlachogiannis ◽  
T.J. Hanratty
Keyword(s):  
Particle Image Velocimetry ◽  
Drag Reduction ◽  
Particle Image ◽  
Image Velocimetry ◽  
Heterogeneous Drag Reduction

Heterogeneous Drag Reduction Concepts and Consequences

1998 ◽  
Vol 120 (4) ◽  
pp. 818-823 ◽  
Author(s):  
Klaus W. Hoyer ◽  
Albert Gyr
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Polymer Solution ◽  
Large Scale ◽  
Scale Interaction ◽  
Polymer Molecules ◽  
Pipe Flows ◽  
Heterogeneous Drag Reduction ◽  
Turbulent Flow Field

This paper deals with the nature of the heterogeneous drag reduction which occurs in turbulent pipe flows when a concentrated polymer solution is injected into the pipe center. According to earlier concepts, the achieved drag reduction is due to a direct, large-scale interaction of the viscoelastic polymer thread with the turbulent flow field. The authors prove that the heterogeneous drag reduction originates exclusively from agglomerates of dissolved polymer molecules present in the flow.

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