We address the phenomenon of drag reduction by a dilute polymeric additive to turbulent flows, using direct numerical simulations (DNS) of the FENE-P model of viscoelastic flows. It had been amply demonstrated that these model equations reproduce the phenomenon, but the results of DNS were not analyzed so far with the goal of interpreting the phenomenon. In order to construct a useful framework for the understanding of drag reduction we initiate in this paper an investigation of the most important modes that are sustained in the viscoelastic and Newtonian turbulent flows, respectively. The modes are obtained empirically using the Karhunen-Loéve decomposition, allowing us to compare the most energetic modes in the viscoelastic and Newtonian flows. The main finding of the present study is that the spatial profile of the most energetic modes is hardly changed between the two flows. What changes is the energy associated with these modes, and their relative ordering in the decreasing order from the most energetic to the least. Modes that are highly excited in one flow can be strongly suppressed in the other, and vice versa. This dramatic energy redistribution is an important clue to the mechanism of drag reduction as is proposed in this paper. In particular, there is an enhancement of the energy containing modes in the viscoelastic flow compared to the Newtonian one; drag reduction is seen in the energy containing modes rather than the dissipative modes, as proposed in some previous theories.
Download full-text PDF |
Source |
|---|---|
| http://dx.doi.org/10.1103/PhysRevE.67.056312 | DOI Listing |
Publication Analysis
Top Keywords
Similar Publications
Analysis of the interaction mechanism between straw soil rotary tillage blade during rotary tillage process.
Sci Rep
January 2025
College of Mechanical and Electrical Engineering, Shihezi University, Shihezi, 832003, China.
In response to the rotary ploughing equipment in the stubble land to implement protective operations, the stubble is large in number and strong in toughness, not easy to crush, resulting in rotary ploughing equipment to produce entanglement and increased resistance to rotary ploughing and other issues. In this study, researchers designed a bionic rotary tillage blade (B-RTB) based on the bionic structural equations of the Marmota claw. A straw-soil complex shear performance test was conducted to investigate the effect of straw on soil shear strength.
View Article and Find Full Text PDFExperimental study on the drag reduction performance of sodium alginate in saline solutions.
Sci Rep
December 2024
Institute for Sustainable Industries and Liveable Cities, Victoria University, Footscray Park Campus Ballarat Road, Footscray, Melbourne, 8001, Australia.
Since the discovery of the turbulence drag reduction phenomenon over 70 years ago, it has been recognized that the addition of small quantities of drag-reducing agents to fluids can significantly decrease wall shear stress, thereby enhancing fluid pumpability. In many applications, the fluids often contain salts, such as those used in fracturing processes within the petroleum sector. The aim of this study is to experimentally investigate the effects of salinity, flow rate, and polymer concentration on the drag reduction performance of sodium alginate in circular pipes.
View Article and Find Full Text PDFImpact of ontogeny and spines on the hydrodynamic performance of the Cambrian arthropod .
R Soc Open Sci
December 2024
Shaanxi Key Laboratory of Early Life and Environments, State Key Laboratory of Continental Dynamics, and Department of Geology, Northwest University, Xi'an 710069, People's Republic of China.
A metazoan-dominated biological pump was established early in the Phanerozoic, a time that saw the evolution of the first pelagic euarthropod zooplankton such as some species of the Cambrian bivalved euarthropod . Pelagic groups evolved from benthic stock, in many cases through neoteny and retention of characteristics from planktic larval stages. However, brooded eggs and did not have a planktic larval stage, precluding this route into the pelagic realm.
View Article and Find Full Text PDFBiomechanics and ontogeny of gliding in wingless stick insect nymphs (Extatosoma tiaratum).
J Exp Biol
December 2024
Department of Integrative Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
Many wingless arboreal arthropods can glide back to tree trunks following free falls. However, little is known about the behaviors and aerodynamics underlying such aerial performance, and how this may be influenced by body size. Here, we studied gliding performance by nymphs of the stick insect Extatosoma tiaratum, focusing on the dynamics of J-shaped trajectories and how gliding capability changes during ontogeny.
View Article and Find Full Text PDFOn-demand zero-drag hydrodynamic cloaks resolve D'Alembert paradox in viscous potential flows.
Microsyst Nanoeng
December 2024
School of Mechanical and Power Engineering, East China University of Science and Technology, Shanghai, 200237, China.
Article Synopsis
- Manipulating fluid flow is crucial for advances in microfluidics, nanoengineering, and biomedicine, and can help address the global energy crisis by achieving zero-drag hydrodynamics.
- The research tackles challenges posed by the D'Alembert paradox and unresolved Navier-Stokes equations, introducing a new type of hydrodynamic cloak that operates with isotropic and homogeneous viscosity.
- Key findings highlight the importance of controlling vorticity for achieving zero-drag and hydrodynamic cloaking, challenging the notion that zero drag is impossible and offering insights beneficial for various technologies, including drug delivery systems.
Want AI Summaries of new PubMed Abstracts delivered to your In-box?
Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!