A Study of the Effect of Polymer Solution in Promoting Friction Reduction in Turbulent Channel Flow

2007 ◽  
Vol 129 (4) ◽  
pp. 491 ◽  
Author(s):  
F. R. Cunha ◽  
M. Andreotti
Keyword(s):  
Polymer Solution ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Friction Reduction

Experimental Study of Polymer Drag Reduction in a Turbulent Channel Flow

2003 ◽  
Author(s):  
Xiaochun Shen ◽  
Kihyun Kim ◽  
Jamison L. Miller ◽  
Ryan Sun-Chee-Fore ◽  
Ana I. Sirviente
Keyword(s):  
Experimental Study ◽  
Polymer Solution ◽  
Channel Flow ◽  
Water Channel ◽  
Turbulent Channel Flow ◽  
Turbulence Characteristics ◽  
Polymer Injection ◽  
Turbulent Channel Flows ◽  
Polymer Drag Reduction ◽  
Turbulent Water

The effect of polymer injection on the turbulence characteristics of a fully developed turbulent water channel flow was studied. The main focus of this study was to assess the influence of the polymer solution injection concentration and consequent mixing. This study was conducted by measuring the turbulence characteristics of two fully developed turbulent channel flows for a Reynolds number of 5×104, with different injection concentrations of the same polymer solution but with the same homogeneous concentration at the test section. These measurements were complemented by visualizations of the flow, which revealed the presence of supra-molecular polymer structures. The development of such structures seems to enhance the drag reducing abilities of the polymer solution.

Drag reduction by linear viscosity model in turbulent channel flow of polymer solution

2008 ◽  
Vol 15 (S1) ◽  
pp. 243-246
Author(s):  
Gui-fen Wu ◽  
Chang-feng Li ◽  
Dong-sheng Huang ◽  
Zuo-guang Zhao ◽  
Xiao-dong Feng ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Polymer Solution ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Viscosity Model

Measurements for Turbulent Channel Flow Containing Microbubbles Using PIV/LIF Technique

2002 ◽  
Author(s):  
Shigeki Nagaya ◽  
Koichi Hishida ◽  
Yoshiaki Kodama ◽  
Akira Kakugawa
Keyword(s):  
Skin Friction ◽  
Channel Flow ◽  
Experimental Approach ◽  
Turbulent Channel Flow ◽  
Friction Reduction ◽  
Wall Turbulence ◽  
Local Skin ◽  
Local Skin Friction ◽  
Turbulent Flow Field ◽  
Skin Friction Reduction

It is known that local skin friction can be reduced by injecting microbubbles into a trubulent boundary layer. However, so far the mechanism of the reduction has never been understood. In the present study, the objective is to understand the characteristics of a turbulent flow field containing microbubbles with an experimental approach in order that the mechanism for the skin friction reduction is clearly elucidated. In order to measure the flow with the microbubbles, a combination of PIV and LIF methods is developed. Measurements are carried out for a horizontal channel flow with microbubbles by which the skin friction is reduced. Modifications of the wall turbulence due to the injection of the microbubbles are discussed.

Linear proportional–integral control for skin-friction reduction in a turbulent channel flow

2017 ◽  
Vol 814 ◽  
pp. 430-451 ◽  
Author(s):  
Euiyoung Kim ◽  
Haecheon Choi
Keyword(s):  
Skin Friction ◽  
Channel Flow ◽  
Flow Model ◽  
Turbulent Channel Flow ◽  
Friction Reduction ◽  
Normal Velocity ◽  
Integral Control ◽  
Velocity Fluctuations ◽  
Proportional Integral ◽  
Skin Friction Reduction

In the present study, we apply a proportional (P)–integral (I) feedback control to a turbulent channel flow for skin-friction reduction. The instantaneous wall-normal velocity at a sensing plane above the wall is measured as a sensing parameter, and blowing/suction is provided at the wall based on the PI control. The performance of PI controls is estimated by the change in the skin friction while varying the sensing plane location $y_{s}$ and the proportional and integral feedback gains ($\unicode[STIX]{x1D6FC}$ and $\unicode[STIX]{x1D6FD}$ respectively). The opposition control proposed by Choi et al. (J. Fluid Mech., vol. 262, 1994, pp. 75–110) corresponds to a P control with $\unicode[STIX]{x1D6FC}=1$. When the sensing plane is located close to the wall ($y_{s}^{+}\lesssim 10$), PI controls result in greater skin-friction reductions than corresponding P controls. The root-mean-square (r.m.s.) sensing velocity fluctuations, considered as the control error, approach zero with successful PI controls, but do not with P controls. Successful PI controls reduce the strength of near-wall coherent structures and the r.m.s. velocity fluctuations above the wall apart from those near the wall due to the control input. The frequency spectra of the sensing velocity show that the I component of PI controls significantly reduces the energy at low frequencies, much more than P controls do. Proportional–integral controls are also applied to a linearized flow model having transient growth of disturbances. The performance of PI controls for a linearized flow model is very similar to that for a turbulent channel flow, i.e. the low-frequency components of disturbances are significantly reduced by the I component of PI controls, and the transient energy growth is suppressed more than by P controls.

scholarly journals Self-sustaining process of minimal attached eddies in turbulent channel flow

2016 ◽  
Vol 795 ◽  
pp. 708-738 ◽  
Author(s):  
Yongyun Hwang ◽  
Yacine Bengana
Keyword(s):  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Turnover Time ◽  
The Self ◽  
Friction Reduction ◽  
Length Scale ◽  
Wall Region ◽  
Streamwise Vortices ◽  
Temporal Oscillation ◽  
Attached Eddies

It has been recently shown that the energy-containing motions (i.e. coherent structures) in turbulent channel flow exist in the form of Townsend’s attached eddies by a numerical experiment which simulates the energy-containing motions only at a prescribed spanwise length scale using their self-sustaining nature (Hwang, J. Fluid Mech., vol. 767, 2015, pp. 254–289). In the present study, a detailed investigation of the self-sustaining process of the energy-containing motions at each spanwise length scale (i.e. the attached eddies) in the logarithmic and outer regions is carried out with an emphasis on its relevance to ‘bursting’, which refers to an energetic temporal oscillation of the motions (Flores & Jiménez, Phys. Fluids, vol. 22, 2010, 071704). It is shown that the attached eddies in the logarithmic and outer regions, composed of streaks and quasi-streamwise vortical structures, bear the self-sustaining process remarkably similar to that in the near-wall region: i.e. the streaks are significantly amplified by the quasi-streamwise vortices via the lift-up effect; the amplified streaks subsequently undergo a ‘rapid streamwise meandering motion’, reminiscent of streak instability or transient growth, which eventually results in breakdown of the streaks and regeneration of new quasi-streamwise vortices. For the attached eddies at a given spanwise length scale ${\it\lambda}_{z}$ between ${\it\lambda}_{z}^{+}\simeq 100$ and ${\it\lambda}_{z}\simeq 1.5h$, the single turnover time period of the self-sustaining process is found to be $Tu_{{\it\tau}}/{\it\lambda}_{z}\simeq 2$ ($u_{{\it\tau}}$ is the friction velocity), which corresponds well to the time scale of the bursting. Two additional numerical experiments, designed to artificially suppress the lift-up effect and the streak meandering motions, respectively, reveal that these processes are essential ingredients of the self-sustaining process of the attached eddies in the logarithmic and outer regions, consistent with several previous theoretical studies. It is also shown that the artificial suppression of the lift-up effect of the attached eddies in the logarithmic and outer regions leads to substantial amounts of turbulent skin-friction reduction.

scholarly journals Turbulent drag reduction through oscillating discs

2014 ◽  
Vol 746 ◽  
pp. 536-564 ◽  
Author(s):  
Daniel J. Wise ◽  
Pierre Ricco
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Oscillation Period ◽  
Friction Reduction ◽  
Wall Turbulence ◽  
Reynolds Stresses ◽  
Disc Diameter ◽  
Tip Velocity

AbstractThe changes in a turbulent channel flow subjected to sinusoidal oscillations of wall flush-mounted rigid discs are studied by means of direct numerical simulations (DNS). The Reynolds number is ${Re}_{\tau }=180$, based on the friction velocity of the stationary-wall case and the half-channel height. The primary effect of the wall forcing is the sustained reduction of wall-shear stress, which reaches a maximum of 20 %. A parametric study on the disc diameter, maximum tip velocity, and oscillation period is presented, with the aim of identifying the optimal parameters which guarantee maximum drag reduction and maximum net energy saving, the latter computed by taking into account the power spent to actuate the discs. This may be positive and reaches 6 %. The Rosenblat viscous pump flow, namely the laminar flow induced by sinusoidal in-plane oscillations of an infinite disc beneath a quiescent fluid, is used to predict accurately the power spent for disc motion in the fully developed turbulent channel flow case and to estimate localized and transient regions over the disc surface subjected to the turbulent regenerative braking effect, for which the wall turbulence exerts work on the discs. The Fukagata–Iwamoto–Kasagi identity is employed effectively to show that the wall-friction reduction is due to two distinguished effects. One effect is linked to the direct shearing action of the near-wall oscillating-disc boundary layer on the wall turbulence, which causes the attenuation of the turbulent Reynolds stresses. The other effect is due to the additional disc-flow Reynolds stresses produced by the streamwise-elongated structures which form between discs and modulate slowly in time. The contribution to drag reduction due to turbulent Reynolds stress attenuation depends on the penetration thickness of the disc-flow boundary layer, while the contribution due to the elongated structures scales linearly with a simple function of the maximum tip velocity and oscillation period for the largest disc diameter tested, a result suggested by the Rosenblat flow solution. A brief discussion on the future applicability of the oscillating-disc technique is also presented.

scholarly journals Prediction of Drag Reduction Rate in Turbulent Channel Flow Based on BP Neural Network

2020 ◽  
Vol 194 ◽  
pp. 05049
Author(s):  
Yuchen Cao ◽  
Yongwen Yang
Keyword(s):  
Neural Network ◽  
Drag Reduction ◽  
Polymer Solution ◽  
Channel Flow ◽  
Bp Neural Network ◽  
Reduction Rate ◽  
Turbulent Channel Flow ◽  
Solution Concentration ◽  
Turbulent Drag Reduction ◽  
Turbulent Drag

The technology of turbulent drag reduction by viscoelastic additives cannot be widely applied in practical engineering due to the difficulty in judging the effect of drag reduction. To solve this problem, the experiment of drag-reducing channel flow of polymer solution was carried out based on the comprehensive analysis of the factors affecting the drag reduction rate. Abundant drag reduction rate data were obtained. A three-layer BP neural network prediction model was established with polymer solution concentration, Reynolds number and injection flow rate as input parameters. Based on the test results, the prediction accuracy on drag reduction rate of the model was analysed. The prediction and model validation of drag reduction rate are carried out further according to the historical data in literature. The results show that the predicted drag reduction rate of BP neural network is close to the real drag reduction rate in the drag-reducing flow of polymer solution. The prediction is with high accuracy and with good generalization ability. It is expected to be applied to practical projects and to promote the development of turbulent drag reduction technology by additives.

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