Two-dimensional dynamics of elasto-inertial turbulence and its role in polymer drag reduction

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.

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Comparison of Turbulent Boundary Layer Profiles Modified With Injection or Uniform Concentration of Drag-Reducing Polymer Solution

Volume 2: Fluid Mechanics; Multiphase Flows ◽

10.1115/fedsm2020-20317 ◽

2020 ◽

Author(s):

Brian R. Elbing

Keyword(s):

Boundary Layer ◽

Turbulent Boundary Layer ◽

Drag Reduction ◽

Polymer Concentration ◽

Weissenberg Number ◽

Polymer Injection ◽

Von Karman ◽

Polymer Properties ◽

Polymer Drag Reduction ◽

Von Kármán

Abstract The current study explores the influence of polymer drag reduction on the near-wall velocity distribution in a turbulent boundary layer. The classical view is that the polymers modify the intercept constant within the log-region without impacting the von Kármán coefficient, which results in the log-region being unaltered though shifted outward from the wall. However, it has been recently shown that this is not accurate, especially at high drag reduction (> 40%). Past work examining the von Kármán coefficient and intercept constant has shown that polymer properties must impact the deviations, but without any quantification of the dependence. This work reviews the literature to make estimates of the local polymer properties and then demonstrates that the scatter at HDR can be attributed to variations in the Weissenberg number. In addition, new polymer ocean results are incorporated and shown to be quite consistent with polymer injection results using the maximum polymer concentration to define the polymer properties.

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Direct Numerical Simulation of Flow around a Circular Cylinder Controlled Using Plasma Actuators

Mathematical Problems in Engineering ◽

10.1155/2014/591807 ◽

2014 ◽

Vol 2014 ◽

pp. 1-13 ◽

Cited By ~ 5

Author(s):

Taichi Igarashi ◽

Hiroshi Naito ◽

Koji Fukagata

Keyword(s):

Numerical Simulation ◽

Circular Cylinder ◽

Direct Numerical Simulation ◽

Drag Reduction ◽

Three Dimensional ◽

Reduction Rate ◽

Plasma Actuators ◽

Two Dimensional ◽

Freestream Velocity ◽

The Mean

Flow around a circular cylinder controlled using plasma actuators is investigated by means of direct numerical simulation (DNS). The Reynolds number based on the freestream velocity and the cylinder diameter is set atReD=1000. The plasma actuators are placed at±90° from the front stagnation point. Two types of forcing, that is, two-dimensional forcing and three-dimensional forcing, are examined and the effects of the forcing amplitude and the arrangement of plasma actuators are studied. The simulation results suggest that the two-dimensional forcing is primarily effective in drag reduction. When the forcing amplitude is higher, the mean drag and the lift fluctuations are suppressed more significantly. In contrast, the three-dimensional forcing is found to be quite effective in reduction of the lift fluctuations too. This is mainly due to a desynchronization of vortex shedding. Although the drag reduction rate of the three-dimensional forcing is slightly lower than that of the two-dimensional forcing, considering the power required for the forcing, the three-dimensional forcing is about twice more efficient.

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A winwin mechanism for low-drag transients in controlled two-dimensional channel flow and its implications for sustained drag reduction

Journal of Fluid Mechanics ◽

10.1017/s0022112003006852 ◽

2004 ◽

Vol 499 ◽

pp. 183-196 ◽

Cited By ~ 23

Author(s):

THOMAS R. BEWLEY ◽

OLE MORTEN AAMO

Keyword(s):

Drag Reduction ◽

Channel Flow ◽

Two Dimensional

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Numerical Simulation of Fluid Slip at a Hydrophobic Surface

Volume 4 ◽

10.1115/ht-fed2004-56046 ◽

2004 ◽

Author(s):

Takao Fujita ◽

Keizo Watanabe

Keyword(s):

Boundary Condition ◽

Laminar Flow ◽

Circular Cylinder ◽

Drag Reduction ◽

Hydrophobic Surface ◽

Friction Reduction ◽

Water Repellent ◽

Two Dimensional ◽

Hydrophobic Property ◽

Flow Past

Laminar drag reduction is achieved by using a hydrophobic surface. In this method, fluid slip is applied at the hydrophobic surface. An initial experiment to clarify for a laminar skin friction reduction was conducted using ducts with a highly water-repellent surface. The surface has a fractal-type structure with many fine grooves. Fluid slip at a hydrophobic surface has been analyzed by applying a new wet boundary condition. In this simulation, an internal flow is assumed to be a two-dimensional laminar flow in a rectangular duct and an external flow is assumed to be a two-dimensional laminar flow past a circular cylinder. The VOF technique has been used as the method for tracking gas-liquid interfaces, and the CSF model has been used as the method for modeling surface tension effects. The wet boundary condition for the hydrophobic property on the surface has been determined from the volume ratio in contact with water near the surface. The model with a stable gas-liquid interface and the experimental results of flow past a circular cylinder at Re = 250 without growing the Karman vortex street are made, and these results show that laminar drag reduction occurring due to fluid slip can be explained in this model.

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