scholarly journals Reynolds number dependence of drag reduction by rodlike polymers

2008 ◽  
Vol 20 (6) ◽  
pp. 065108 ◽  
Author(s):  
Yacine Amarouchene ◽  
Daniel Bonn ◽  
Hamid Kellay ◽  
Ting-Shek Lo ◽  
Victor S. L’vov ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Drag Reduction ◽  
Rodlike Polymers ◽  
Reynolds Number Dependence

scholarly journals Microbubbly drag reduction in Taylor–Couette flow in the wavy vortex regime

2008 ◽  
Vol 608 ◽  
pp. 21-41 ◽  
Author(s):  
KAZUYASU SUGIYAMA ◽  
ENRICO CALZAVARINI ◽  
DETLEF LOHSE
Keyword(s):  
Reynolds Number ◽  
Drag Reduction ◽  
Couette Flow ◽  
Physical Mechanism ◽  
Dilute Suspensions ◽  
Fluid Coupling ◽  
Taylor Couette ◽  
The Individual ◽  
Reynolds Number Dependence ◽  
Taylor Couette Flow

We investigate the effect of microbubbles on Taylor–Couette flow by means of direct numerical simulations. We employ an Eulerian–Lagrangian approach with a gas–fluid coupling based on the point-force approximation. Added mass, drag, lift and gravity are taken into account in the modelling of the motion of the individual bubble. We find that very dilute suspensions of small non-deformable bubbles (volume void fraction below 1%, zero Weber number and bubble Reynolds number ≲10) induce a robust statistically steady drag reduction (up to 20%) in the wavy vortex flow regime (Re=600–2500). The Reynolds number dependence of the normalized torque (the so-called torque reduction ratio (TRR) which corresponds to the drag reduction) is consistent with a recent series of experimental measurements performed by Murai et al. (J. Phys. Conf. Ser. vol. 14, 2005, p. 143). Our analysis suggests that the physical mechanism for the torque reduction in this regime is due to the local axial forcing, induced by rising bubbles, that is able to break the highly dissipative Taylor wavy vortices in the system. We finally show that the lift force acting on the bubble is crucial in this process. When it is neglected, the bubbles preferentially accumulate near the inner cylinder and the bulk flow is less efficiently modified. Movies are available with the online version of the paper.

scholarly journals Investigation of a drag reduction on a circular cylinder in rotary oscillation

2001 ◽  
Vol 431 ◽  
pp. 297-322 ◽  
Author(s):  
D. SHIELS ◽  
A. LEONARD
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Drag Reduction ◽  
Vortex Method ◽  
Reynolds Numbers ◽  
Reduction Procedure ◽  
Two Dimensional Flow ◽  
The Impact ◽  
Reynolds Number Dependence ◽  
Cylinder Rotation

Drag reduction in two-dimensional flow over a circular cylinder, achieved using rotary oscillation, was investigated with computational simulations. In the experiments of Tokumaru & Dimotakis (1991), this mechanism was observed to yield up to 80% drag reduction at Re = 15 000 for certain ranges of frequency and amplitude of sinusoidal rotary oscillation. Simulations with a high-resolution viscous vortex method were carried out over a range of Reynolds numbers (150–15 000) to explore the effects of oscillatory rotational forcing. Significant drag reduction was observed for a rotational forcing which had been very effective in the experiments. The impact of the forcing is strongly Reynolds number dependent. The cylinder oscillation appears to trigger a distinctive shedding pattern which is related to the Reynolds number dependence of the drag reduction. It appears that the source of this unusual shedding pattern and associated drag reduction is vortex dynamics in the boundary layer initiated by the oscillatory cylinder rotation. The practical efficiency of the drag reduction procedure is also discussed.

High Reynolds Number Micro-Bubble and Polymer Drag Reduction Experiments

2008 ◽  
Author(s):  
Steven L. Ceccio ◽  
David R. Dowling ◽  
Marc Perlin ◽  
Michael Solomon
Keyword(s):  
Reynolds Number ◽  
Drag Reduction ◽  
High Reynolds Number ◽  
Polymer Drag Reduction ◽  
Micro Bubble ◽  
High Reynolds

scholarly journals Noise Reduction Effect of Superhydrophobic Surfaces with Streamwise Strip of Channel Flow

2021 ◽  
Vol 11 (9) ◽  
pp. 3869
Author(s):  
Chen Niu ◽  
Yongwei Liu ◽  
Dejiang Shang ◽  
Chao Zhang
Keyword(s):  
Reynolds Number ◽  
Drag Reduction ◽  
Noise Reduction ◽  
Channel Flow ◽  
Superhydrophobic Surface ◽  
Sound Field ◽  
Flow Noise ◽  
Slip Boundary ◽  
Eddy Simulation ◽  
Reduction Effect

Superhydrophobic surface is a promising technology, but the effect of superhydrophobic surface on flow noise is still unclear. Therefore, we used alternating free-slip and no-slip boundary conditions to study the flow noise of superhydrophobic channel flows with streamwise strips. The numerical calculations of the flow and the sound field have been carried out by the methods of large eddy simulation (LES) and Lighthill analogy, respectively. Under a constant pressure gradient (CPG) condition, the average Reynolds number and the friction Reynolds number are approximately set to 4200 and 180, respectively. The influence on noise of different gas fractions (GF) and strip number in a spanwise period on channel flow have been studied. Our results show that the superhydrophobic surface has noise reduction effect in some cases. Under CPG conditions, the increase in GF increases the bulk velocity and weakens the noise reduction effect. Otherwise, the increase in strip number enhances the lateral energy exchange of the superhydrophobic surface, and results in more transverse vortices and attenuates the noise reduction effect. In our results, the best noise reduction effect is obtained as 10.7 dB under the scenario of the strip number is 4 and GF is 0.5. The best drag reduction effect is 32%, and the result is obtained under the scenario of GF is 0.8 and strip number is 1. In summary, the choice of GF and the number of strips is comprehensively considered to guarantee the performance of drag reduction and noise reduction in this work.

scholarly journals Reynolds number dependence of Lyapunov exponents of turbulence and fluid particles

2021 ◽  
Vol 103 (3) ◽  
Author(s):  
Itzhak Fouxon ◽  
Joshua Feinberg ◽  
Petri Käpylä ◽  
Michael Mond
Keyword(s):  
Reynolds Number ◽  
Lyapunov Exponents ◽  
Fluid Particles ◽  
Reynolds Number Dependence

Effect of Reynolds number on drag reduction in turbulent boundary layer flow over liquid–gas interface

2020 ◽  
Vol 32 (12) ◽  
pp. 122111
Author(s):  
Hongyuan Li ◽  
SongSong Ji ◽  
Xiangkui Tan ◽  
Zexiang Li ◽  
Yaolei Xiang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Drag Reduction ◽  
Boundary Layer Flow ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

scholarly journals Fibre-induced drag reduction

2008 ◽  
Vol 602 ◽  
pp. 209-218 ◽  
Author(s):  
J. J. J. GILLISSEN ◽  
B. J. BOERSMA ◽  
P. H. MORTENSEN ◽  
H. I. ANDERSSON
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Drag Reduction ◽  
Elastic Layer ◽  
Turbulent Drag Reduction ◽  
Rigid Polymer ◽  
Fibre Concentration ◽  
Induced Drag ◽  
Turbulent Drag

We use direct numerical simulation to study turbulent drag reduction by rigid polymer additives, referred to as fibres. The simulations agree with experimental data from the literature in terms of friction factor dependence on Reynolds number and fibre concentration. An expression for drag reduction is derived by adopting the concept of the elastic layer.

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