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 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.

Analytical Upper Limit of Drag Reduction With Polymer Additives in Turbulent Pipe Flow

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Xin Zhang ◽  
Xili Duan ◽  
Yuri Muzychka
Keyword(s):  
Mathematical Model ◽  
Drag Reduction ◽  
Pipe Flow ◽  
Critical Concentration ◽  
Turbulent Pipe Flow ◽  
Chemical Additives ◽  
Upper Limit ◽  
Maximum Drag Reduction ◽  
Flow Drag ◽  
Nonlinear Elastic

Flow drag reduction induced by chemical additives, more commonly called drag-reducing agents (DRAs), has been studied for many years, but few studies can manifest the mechanism of this phenomenon. In this paper, a new mathematical model is proposed to predict the upper limit of drag reduction with polymer DRAs in a turbulent pipe flow. The model is based on the classic finitely extensible nonlinear elastic-Peterlin (FENE-P) theory, with the assumption that all vortex structures disappear in the turbulent flow, i.e., complete laminarization is achieved. With this model, the maximum drag reduction by a DRA at a given concentration can be predicted directly with several parameters, i.e., bulk velocity of the fluid, pipe size, and relaxation time of the DRA. Besides, this model indicates that both viscosity and elasticity contribute to the drag reduction: before a critical concentration, both viscosity and elasticity affect the drag reduction positively; after this critical concentration, elasticity still works as before but viscosity affects drag reduction negatively. This study also proposes a correlation format between drag reduction measured in a rheometer and that estimated in a pipeline. This provides a convenient way of pipeline drag reduction estimation with viscosity and modulus of the fluids that can be easily measured in a rheometer.

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.

Shark-skin surfaces for fluid-drag reduction in turbulent flow: a review

2010 ◽  
Vol 368 (1929) ◽  
pp. 4775-4806 ◽  
Author(s):  
Brian Dean ◽  
Bharat Bhushan
Keyword(s):  
Turbulent Flow ◽  
Drag Reduction ◽  
Performance Studies ◽  
Flow Characteristics ◽  
Shark Skin ◽  
Turbulent Flow Regime ◽  
Fluid Drag ◽  
Maximum Drag Reduction ◽  
Manufacturing Techniques ◽  
Fluid Flow Characteristics

The skin of fast-swimming sharks exhibits riblet structures aligned in the direction of flow that are known to reduce skin friction drag in the turbulent-flow regime. Structures have been fabricated for study and application that replicate and improve upon the natural shape of the shark-skin riblets, providing a maximum drag reduction of nearly 10 per cent. Mechanisms of fluid drag in turbulent flow and riblet-drag reduction theories from experiment and simulation are discussed. A review of riblet-performance studies is given, and optimal riblet geometries are defined. A survey of studies experimenting with riblet-topped shark-scale replicas is also given. A method for selecting optimal riblet dimensions based on fluid-flow characteristics is detailed, and current manufacturing techniques are outlined. Due to the presence of small amounts of mucus on the skin of a shark, it is expected that the localized application of hydrophobic materials will alter the flow field around the riblets in some way beneficial to the goals of increased drag reduction.

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.

Sign in / Sign up

Export Citation Format

Share Document