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.

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.

scholarly journals On the structure of streamwise wall-shear stress fluctuations in turbulent channel flows

2020 ◽  
Vol 1522 ◽  
pp. 012010
Author(s):  
Cheng Cheng ◽  
Weipeng Li ◽  
Adrián Lozano-Durán ◽  
Yitong Fan ◽  
Hong Liu
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Channel Flows ◽  
Turbulent Channel Flows ◽  
Wall Shear

Numerical and theoretical investigation of pulsatile turbulent channel flows

2016 ◽  
Vol 792 ◽  
pp. 98-133 ◽  
Author(s):  
Chenyang Weng ◽  
Susann Boij ◽  
Ardeshir Hanifi
Keyword(s):  
Shear Stress ◽  
Reynolds Shear Stress ◽  
Nonlinear Effects ◽  
Turbulent Channel Flow ◽  
Theoretical Models ◽  
Phase Lag ◽  
Reynolds Stresses ◽  
Turbulent Eddies ◽  
Turbulent Channel Flows ◽  
Physical Features

A turbulent channel flow subjected to imposed harmonic oscillations is studied by direct numerical simulation (DNS) and theoretical models. Simulations have been performed for different pulsation frequencies. The time- and phase-averaged data have been used to analyse the flow. The onset of nonlinear effects during the production of the perturbation Reynolds stresses is discussed based on the DNS data, and new physical features observed in the DNS are reported. A linear model proposed earlier by the present authors for the coherent perturbation Reynolds shear stress is reviewed and discussed in depth. The model includes the non-equilibrium effects during the response of the Reynolds stress to the imposed periodic shear straining, where a phase lag exists between the stress and the strain. To validate the model, the perturbation velocity and Reynolds shear stress from the model are compared with the DNS data. The performance of the model is found to be good in the frequency range where quasi-static assumptions are invalid. The viscoelastic characteristics of the turbulent eddies implied by the model are supported by the DNS data. Attempts to improve the model are also made by incorporating the DNS data in the model.

Suboptimal control of turbulent channel flow for drag reduction

1998 ◽  
Vol 358 ◽  
pp. 245-258 ◽  
Author(s):  
CHANGHOON LEE ◽  
JOHN KIM ◽  
HAECHEON CHOI
Keyword(s):  
Shear Stress ◽  
Feedback Control ◽  
Drag Reduction ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Suboptimal Control ◽  
Local Distribution ◽  
Friction Drag ◽  
Control Laws ◽  
Simple Feedback

Two simple feedback control laws for drag reduction are derived by applying a suboptimal control theory to a turbulent channel flow. These new feedback control laws require pressure or shear-stress information only at the wall, and when applied to a turbulent channel flow at Reτ=110, they result in 16–22% reduction in the skin-friction drag. More practical control laws requiring only the local distribution of the wall pressure or one component of the wall shear stress are also derived and are shown to work equally well.

DNS of Drag-Reducing Turbulent Channel Flow With Coexisting Newtonian and Non-Newtonian Fluid

2005 ◽  
Vol 127 (5) ◽  
pp. 929-935 ◽  
Author(s):  
Bo Yu ◽  
Yasuo Kawaguchi
Keyword(s):  
Shear Stress ◽  
Reynolds Shear Stress ◽  
Flow Region ◽  
Turbulent Channel Flow ◽  
Turbulent Convection ◽  
Turbulent Channel Flows ◽  
Entire Flow ◽  
Shear Induced Structure ◽  
Induced Structure ◽  
And Diffusion

In the present study, we numerically investigated drag-reducing turbulent channel flows by surfactant additives. Surfactant additives were assumed to be uniformly distributed in the entire flow region by turbulent convection and diffusion, etc., but it was assumed that the shear-induced structure (SIS) (network of rod-like micelles) could form either in the region next to the walls or in the center region of the channel, making the fluid viscoelastic. In other regions surfactant additives were assumed to be incapable of building a network structure, and to exist in the form of molecules or micelles that do not affect the Newtonian properties of the fluid. With these assumptions, we studied the drag-reducing phenomenon with coexisting Newtonian and non-Newtonian fluids. From the study we identified the effectiveness of the network structures at different flow regions, and showed that the phenomenon of drag-reduction (DR) by surfactant additives is not only closely associated with the reduction of Reynolds shear stress but also related to the induced viscoelastic shear stress.

Novel and Enviromentaly Friendly Mechanical Technique to Improve the Flow in Water Pipelienes

2011 ◽  
Vol 347-353 ◽  
pp. 3029-3035
Author(s):  
Hayder A. Abdulbari ◽  
Rosli Bin Mohd Yunus ◽  
Zulkafli Bin Hassan ◽  
Wafaa Kamil Mahmood ◽  
C Hooi
Keyword(s):  
Experimental Investigation ◽  
Stainless Steel ◽  
Shear Stress ◽  
Fluid Flow ◽  
Drag Reduction ◽  
Stress Reduction ◽  
Aqueous Media ◽  
Turbulent Channel Flow ◽  
Friction Drag ◽  
Set Up

The paper is concerned with an experimental investigation of the drag reduction in turbulent channel flow over the mechanical chain. A circulating loop for the fluid flow with 0.0381 inside diameter of pipe is set up. The testing length of the system is 1.5m.Wall shear stress reduction performance has been investigated experimentally for various design geometry surfaces including a replica of bent consisting of stainless steel model scales. Attempts to optimize the net drag reduction by varying the design geometry and alignment are also discussed. The study indicated that the mechanical chain taken in water flow is capable to decrease the friction drag of a turbulent flow up to 40%. The maximum percentage was achieved in 39.37L/D at RE equal to 56733. The results show that a substantial drag reduction can be achieved by this mechanical chain in aqueous media.

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