Transition to turbulence in pipe flow for water and dilute solutions of polyethylene oxide

1972 ◽  
Vol 51 (1) ◽  
pp. 177-185 ◽  
Author(s):  
R. W. Paterson ◽  
F. H. Abernathy
Keyword(s):  
Turbulent Flow ◽  
Drag Reduction ◽  
Polyethylene Oxide ◽  
Transition To Turbulence ◽  
Small Scale ◽  
Outer Flow ◽  
Pure Solvent ◽  
Inlet Conditions ◽  
Scale Turbulence ◽  
Flow Drag

An experimental study of the transition from laminar to turbulent flow in a long 0·248in. I.D. pipe is reported for both water and dilute water solutions of polyethylene oxide which exhibit turbulent flow drag reduction (the Toms phenomenon). The drag-reducing solutions, ranging in effectiveness from near zero to the maximum attainable, are observed to undergo transition in a similar way to the Newtonian solvent in that the solutions exhibit intermittency and the growth rates of the turbulent patches are essentially equal to those of the pure solvent. The growth rate of turbulent patches indicates that drag reduction is associated with the small-scale structure of the turbulence near the pipe wall while patch growth is associated with the larger-scale turbulence in the outer flow. For low-disturbance pipe inlet conditions the strong drag-reducing solutions are observed to undergo transition at lower Reynolds numbers than the pure solvent.

Wavelet Analysis on Eddy Structure in Micro Bubble Two Phase Flow Using PIV

2004 ◽  
Author(s):  
Ling Zhen ◽  
Claudia del Carmen Gutierrez-Torres
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Large Scale ◽  
Operating Conditions ◽  
Small Scale ◽  
Turbulent Structures ◽  
Two Phase ◽  
Multi Scale ◽  
Eddy Structures

The question of “where and how the turbulent drag arises” is one of the most fundamental problems unsolved in fluid mechanics. However, the physical mechanism responsible for the friction drag reduction is still not well understood. Over decades, it is found that the turbulence production and self-containment in a boundary layer are organized phenomena and not random processes as the turbulence looks like. The further study in the boundary layer should be able to help us know more about the mechanisms of drag reduction. The wavelet-based vector multi-resolution technique was proposed and applied to the two dimensional PIV velocities for identifying the multi-scale turbulent structures. The intermediate and small scale vortices embedded within the large-scale vortices were separated and visualized. By analyzing the fluctuating velocities at different scales, coherent eddy structures were obtained and this help us obtain the important information on the multi-scale flow structures in the turbulent flow. By comparing the eddy structures in different operating conditions, the mechanism to explain the drag reduction caused by micro bubbles in turbulent flow was proposed.

Turbulent flow drag reduction and degradation with dilute polymer solutions

1970 ◽  
Vol 43 (4) ◽  
pp. 689-710 ◽  
Author(s):  
R. W. Paterson ◽  
F. H. Abernathy
Keyword(s):  
Molecular Weight ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Average Molecular Weight ◽  
Experimental Studies ◽  
Polymer Degradation ◽  
High Viscosity ◽  
Turbulent Pipe Flow ◽  
Shear Stresses ◽  
Flow Drag

Experimental studies of drag reduction and polymer degradation in turbulent pipe flow with dilute water solutions of unfractionated polyethylene oxide are described. Drag reduction results indicate that the magnitude of the reduction cannot be correlated on the basis of weight average molecular weight, rather the phenomenon depends strongly on the concentration of the highest molecular weight species present in the molecular weight distribution. Polymer degradation in turbulent flow is found to be severe for high molecular weight polymers causing appreciable changes in drag reduction and molecular weight with the duration of flow. Data indicates that drag reduction exists in the limit of infinite dilution suggesting that the phenomenon is due to the interaction of individual polymer molecules with the surrounding solvent and that the extent of reduction is relatively independent of pipe diameter when a comparison is carried out at equal solvent wall shear stresses. Consideration of the high viscosity obtained with solutions in an irrotational laminar flow field suggests this is due to polymer molecule deformation and that this phenomenon is central to the mechanism of turbulent flow drag reduction.

scholarly journals Study on the Law of Pseudo-Cavitation on Superhydrophobic Surface in Turbulent Flow Field of Backward-Facing Step

Fluids ◽  
2021 ◽  
Vol 6 (6) ◽  
pp. 200
Author(s):  
Xuecheng Lv ◽  
Wei-Tao Wu ◽  
Jizu Lv ◽  
Ke Mao ◽  
Linsong Gao ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Superhydrophobic Surface ◽  
Large Bubble ◽  
Backward Facing Step ◽  
Bubble Generation ◽  
Turbulent Flow Field ◽  
Flow Drag

Superhydrophobic surface is regarded as important topic in the field of thermal fluids today due to its unique features on flow drag reduction and heat transfer enhancement. In this study, the pseudo-cavitation phenomenon on the superhydrophobic surface in the backward-facing step turbulent flow field is observed through experiments. The underlying reason for this phenomenon is studied with experimental observation and analysis, and the time variant mechanisms of this phenomenon with various Reynolds number is summarized. The research results indicate that the superhydrophobic surface and the backward-facing step provide the material basis and dynamic condition for the generation of pseudo-cavitation. The pseudo-cavitation induces a large bubble on the superhydrophobic surface below the backward-facing step. The size, position, shape, oscillation amplitude, detachment, and splitting of the large bubble show regularity with the changes of Reynolds number. Meanwhile, the bubble growth, oscillation, detachment, split, and regeneration over time also show regularity. The study of bubble generation and development laws can be used to better control the perturbation of the flow field. Importantly, the present study has meaning in better understanding the flow mechanisms and gas coverage of superhydrophobic surface under condition of backward-facing step, paving the way for studying the flow drag reduction effect of superhydrophobic surface.

scholarly journals A note to further explain the mechanism of turbulent flow drag reduction by polymer from chemistry view

2021 ◽  
Author(s):  
Xin Zhang ◽  
Xiaodong Dai ◽  
Jishi Zhao ◽  
Dengwei Jing ◽  
Fei Liu ◽  
...  
Keyword(s):  
Fourier Series ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Phase Angle ◽  
Linear Polymers ◽  
Flexible Polymers ◽  
Viscoelastic Theory ◽  
Maximum Drag Reduction ◽  
Flow Drag ◽  
Drag Reducing Polymer

In our previous work regarding the mechanism of drag reduction and degradation by flexible linear polymers, we proposed a correlation based on the Fourier series to predict the drag reduction and its degradation, where a phase angle was involved, but the physical meaning for the correlation especially of the employed phase angle was not clear, which is however important for reasonable explanation of the drag reduction mechanism over flexible linear polymers. This letter aims to clarify this issue. We use several steps of deduction from the viscoelastic theory, and conclude that the Fourier series employed to predict the drag reduction and its degradation is due to viscoelastic property of drag-reducing polymer solution, and the phase angle represents the hysteresis of polymer in turbulent flow. Besides, our new view of drag reduction by flexible polymers can also explain why a maximum drag reduction in rotational flow appears before degradation happens.

Turbulent Flow of Drag Reducing Fluids Between Concentric Rotating Cylinders

1972 ◽  
Vol 1 (1) ◽  
pp. 25-30 ◽  
Author(s):  
E. Bilgen ◽  
R. Boulos
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Polyethylene Oxide ◽  
Guar Gum ◽  
Rotating Cylinder ◽  
Large Reynolds Number ◽  
Reduction Mechanism ◽  
Dilute Solutions ◽  
Concentric Cylinders

The turbulent flow of drag reducing fluids between concentric cylinders, the inner cylinder rotating and the outer one at rest, has been studied experimentally. The drag reducing fluids were dilute solutions of polyethylene oxide, polyacrylamide and guar gum. The torques exerted by the inner rotating cylinder have been measured for various gap widths and over a relatively large Reynolds number. The results have been reduced in dimensionless parameters and correlated. The velocity profiles between the cylinders have also been measured and the drag reduction mechanism has been discussed briefly.

Mechanism of Flow Drag Reduction on Non-Smooth Surface

2013 ◽  
Author(s):  
Beibei Feng ◽  
Darong Chen ◽  
Jiadao Wang ◽  
Xingtuan Yang
Keyword(s):  
Drag Reduction ◽  
Smooth Surface ◽  
Reynolds Shear Stress ◽  
Dominant Factor ◽  
Adjacent Area ◽  
Flow Shear ◽  
Outer Flow ◽  
Flow Alteration ◽  
Pressure Drag ◽  
Flow Drag

Numerical simulations of air flow were carried out on non-smooth surface where microriblets were distributed uniformly at only one of the walls. An accurate numerical treatment based on k-ε turbulence model was adopted to study flow alteration and to analyze drag reduction and increasing mechanism on non-smooth surface. A modified calculation unit was used to estimate characteristics of flow at the reformed cells. With the microriblets aligned on the surface, the Reynolds shear stress was significantly decreased which was considered the dominant factor resulting in drag reduction. An additional force generating from the deviation of static pressure on the front and rear end of the riblet grooves caused pressure drag increasing exhibiting exponential growth with the flow rate, which was closely related to vortices induced by momentum transfer at the adjacent area of flow inside the grooves and the outer flow. Shear action at groove walls was greatly degraded due to the gradually variational velocity of vortices. Flow alteration on non-smooth surface compared with smooth surface was also analyzed in detail.

scholarly journals Flexible conformable hydrophobized surfaces for turbulent flow drag reduction

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
Joseph C Brennan ◽  
Nicasio R Geraldi ◽  
Robert H Morris ◽  
David J Fairhurst ◽  
Glen McHale ◽  
...  
Keyword(s):  
Turbulent Flow ◽  
Drag Reduction ◽  
Flow Drag

Characterization of superhydrophobic surfaces for drag reduction in turbulent flow

2018 ◽  
Vol 845 ◽  
pp. 560-580 ◽  
Author(s):  
James W. Gose ◽  
Kevin Golovin ◽  
Mathew Boban ◽  
Joseph M. Mabry ◽  
Anish Tuteja ◽  
...  
Keyword(s):  
Contact Angle ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Rational Design ◽  
Ambient Pressure ◽  
Contact Angle Hysteresis ◽  
Superhydrophobic Surfaces ◽  
Small Scale ◽  
Flow Conditions ◽  
Number Range

A significant amount of the fuel consumed by marine vehicles is expended to overcome skin-friction drag resulting from turbulent boundary layer flows. Hence, a substantial reduction in this frictional drag would notably reduce cost and environmental impact. Superhydrophobic surfaces (SHSs), which entrap a layer of air underwater, have shown promise in reducing drag in small-scale applications and/or in laminar flow conditions. Recently, the efficacy of these surfaces in reducing drag resulting from turbulent flows has been shown. In this work we examine four different, mechanically durable, large-scale SHSs. When evaluated in fully developed turbulent flow, in the height-based Reynolds number range of 10 000 to 30 000, significant drag reduction was observed on some of the surfaces, dependent on their exact morphology. We then discuss how neither the roughness of the SHSs, nor the conventional contact angle goniometry method of evaluating the non-wettability of SHSs at ambient pressure, can predict their drag reduction under turbulent flow conditions. Instead, we propose a new characterization parameter, based on the contact angle hysteresis at higher pressure, which aids in the rational design of randomly rough, friction-reducing SHSs. Overall, we find that both the contact angle hysteresis at higher pressure, and the non-dimensionalized surface roughness, must be minimized to achieve meaningful turbulent drag reduction. Further, we show that even SHSs that are considered hydrodynamically smooth can cause significant drag increase if these two parameters are not sufficiently minimized.

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