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 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.

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

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.

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.

Numerical Simulation of High Drag Reduction Regime in Polymer Solutions (Keynote)

2003 ◽  
Author(s):  
Yves Dubief ◽  
Christopher M. White ◽  
Vincent E. Terrapon ◽  
Eric S. G. Shaqfeh ◽  
Sanjiva K. Lele ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Drag Reduction ◽  
Polymer Solutions ◽  
Domain Size ◽  
Channel Flows ◽  
Vortical Structures ◽  
Convergence And Stability ◽  
Subsequent Modification ◽  
Stability Of The Solution

The simulation of drag reduced channel flows has to rely on consitituve models such as FENE-P. Their implementation is not straightforward to achieve convergence and stability of the solution. This paper discusses the problem of advection embedded in the FENE-P equation and the issue of the domain size. Finally we present results of simulations for High Drag Reduction regime, and show the subsequent modification of the vortical structures.

scholarly journals Effect of finite Weissenberg number on turbulent channel flows of an elastoviscoplastic fluid

2021 ◽  
Vol 927 ◽  
Author(s):  
Daulet Izbassarov ◽  
Marco E. Rosti ◽  
Luca Brandt ◽  
Outi Tammisola
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Weissenberg Number ◽  
Channel Flows ◽  
Viscoplastic Flow ◽  
Turbulent Structures ◽  
Turbulent Dissipation ◽  
Flow Equations ◽  
Turbulent Channel Flows ◽  
Nonlinear Elastic

Direct numerical simulations are carried out to study the effect of finite Weissenberg number up to $Wi=16$ on laminar and turbulent channel flows of an elastoviscoplastic (EVP) fluid, at a fixed bulk Reynolds number of $2800$ . The incompressible flow equations are coupled with the evolution equation for the EVP stress tensor by a modified Saramito model that extends both the Bingham viscoplastic and the finite extensible nonlinear elastic-Peterlin (FENE-P) viscoelastic models. In turbulent flow, we find that drag decreases with both the Bingham and Weissenberg numbers, until the flow laminarises at high enough elastic and yield stresses. Hence, a higher drag reduction is achieved than in the viscoelastic flow at the same Weissenberg number. The drag reduction persists at Bingham numbers up to 20, in contrast to viscoplastic flow, where the drag increases in the laminar regime compared with a Newtonian flow. Moreover, elasticity affects the laminarisation of an EVP flow in a non-monotonic fashion, delaying it at lower and promoting it at higher Weissenberg numbers. A hibernation phenomenon is observed in the EVP flow, leading to large changes in the unyielded regions. Finally, plasticity is observed to affect both low- and high-speed streaks equally, attenuating the turbulent dissipation and the fragmentation of turbulent structures.

Frictional drag reduction promoted by generating void waves in high-speed turbulent channel flows

2019 ◽  
Vol 2019.24 (0) ◽  
pp. A122
Author(s):  
Taiji TANAKA ◽  
Hyun Jin PARK ◽  
Yuji TASAKA ◽  
Yuichi MURAI ◽  
Chiharu KAWAKITA
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Channel Flows ◽  
Frictional Drag ◽  
Turbulent Channel Flows

scholarly journals Polymer drag reduction in surfactant-contaminated turbulent bubbly channel flows

2021 ◽  
Vol 6 (10) ◽  
Author(s):  
Daulet Izbassarov ◽  
Zaheer Ahmed ◽  
Pedro Costa ◽  
Ville Vuorinen ◽  
Outi Tammisola ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Channel Flows ◽  
Polymer Drag Reduction
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