Turbulent drag reduction by polymer‐fiber mixtures

Malhotra, J. P.; Deshmukh, S. R.; Singh, R. P.

doi:10.1002/app.1987.070330716

Cited by 11 publications

(3 citation statements)

References 12 publications

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“…They also were able to exceed the maximum drag reduction asymptote of Virk, Mickley & Smith (1970). This effect was also observed by other investigators using both polymer-fibre mixtures (Malhotra, Deshmukh & Singh 1987) and mixtures of rigid and flexible polymers (Dingilian & Ruckenstein 1974;Reddy & Singh 1985). This synergy led Metzner (Kale & Metzner 1976;Metzner 1977) to speculate that fibres and polymers reduced turbulent drag by different mechanisms and that the action of fibres was related to extensional resistance in near-wall turbulent structures, which were poorly characterized at that time.…”

Section: Introductionsupporting

confidence: 74%

Numerical simulation of turbulent drag reduction using rigid fibres

et al. 2004

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We present a study of the drag reduction induced by rigid fibres in a turbulent channel flow using direct numerical simulation. The extra stresses due to the fibres are calculated with the well-known constitutive equation involving the moments of the orientation vector. Drag reductions of up to 26% are calculated, with the largest drag reductions observed using non-Brownian fibres and semi-dilute concentrations. These findings suggest that elasticity is not necessary to achieve turbulent drag reduction. Flow statistics show trends similar to those observed in simulation of polymeric drag reduction: Reynolds stresses are reduced, velocity fluctuations in the wall-normal and spanwise directions are reduced while streamwise fluctuations are increased, and streamwise vorticity is reduced. We observe strong correlations between the fibre stresses and inter-vortex extensional flow regions. Based on these correlations and instantaneous visualizations of the flow field, we propose a mechanism for turbulent drag reduction by rigid fibre additives.

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Section: Introductionsupporting

confidence: 74%

Numerical simulation of turbulent drag reduction using rigid fibres

et al. 2004

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“…The product, BC, is a polymer, and a synergistic effect of drag reduction by BC is expected (22,23). However the main production stage of BC was after the logarithmic growth phase and the effect mentioned above is not primarily important for BC production.…”

Section: Discussionmentioning

confidence: 99%

Effect of Addition of Water-Soluble Polysaccharides on Bacterial Cellulose Production in a 50-L Airlift Reactor

et al. 2001

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Bacterial cellulose (BC) production was carried out in a batch cultivation of Acetobacter xylinum in a 50-L internal loop airlift reactor by addition of water-soluble polysaccharides into the medium. When 0.1% (w/w) agar was added, BC production reached 8.7 g/L compared with 6.3 g/L in the control, and duration of the cultivation period to reach the maximum concentration of BC was almost half of that without addition of polysaccharides. During cultivation, BC was formed into pellets whose size was smaller when the productivity of BC was higher, indicating that increase in the relative viscosity by addition of polysaccharides hindered formation of large clumps of BC and increase in the volumetric oxygen transfer coefficient at high flow rate led to increase in BC productivity.

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“…Fiber additives are more resistant to shear degradation than flexible polymers. This robustness has led to some studies of mixtures of fibers and polymers in an attempt to develop an additive blend that is more shearresistant than flexible polymers alone (Lee et al, 1974;Metzner, 1977;Malhotra et al, 1987). These mixtures not only exhibit greater shear resistance but also dramatically increase the amount of drag-reduction.…”

Section: Introductionmentioning

confidence: 99%

Polymer induced drag reduction in exact coherent structures of plane Poiseuille flow

Graham

2007

Physics of Fluids

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Nonlinear traveling waves that are precursors to laminar-turbulent transition and capture the main structures of the turbulent buffer layer have recently been found to exist in all the canonical parallel flow geometries. The present work examines the effect of polymer additives on these "exact coherent states" (ECS) in the plane Poiseuille geometry, using the FENE-P constitutive model for polymer solutions. In experiments with a given fluid, Reynolds and Weissenberg numbers are linearly related (i.e. Wi/Re = const).In this situation, we study the effects of viscoelasticity on velocity field and polymer stress field along some experimental paths, which represent different flow behaviors as Re (and Wi) increases. The changes to the velocity field for the viscoelastic nonlinear traveling waves qualitatively capture many of those experimentally observed in fully turbulent flows of polymer solutions at low to moderate levels of drag reduction: drag is reduced, streamwise velocity fluctuations increase, wall-normal and spanwise velocity fluctuations decrease. The mechanism underlying these observations is the suppression of streamwise vortices by the polymer forces exerted on the fluid. Specifically, at sufficiently high wall shear rates, viscoelasticity completely suppress these streamwise vortices in the near-wall region, as is found in experiments in the maximum drag reduction (MDR) regime. The mean shear stress balance for the nonlinear traveling waves show that Reynolds shear stress decreases and polymer stress increases monotonically with the increase of viscoelasticity, as are found in full turbulence. The study of the influence of the viscoelasticity on the turbulent kinetic energy and Reynolds stress budgets shows that as Re (and Wi) increases, there is a consistent decrease in the production, diffusion and dissipation of turbulent kinetic energy. The decrease in the velocity pressure gradient term leads to a redistribution of the turbulent kinetic energy among the streamwise, iii wall-normal and spanwise directions. The influence of the rheological parameters on the viscoelastic ECS is analyzed. It is found that the degree of drag reduction is determined primarily by the extensional viscosity and Weissenberg number. The optimum wavelength conditions under which the viscoelastic ECS first come into existence are also investigated. The wavelengths in streamwise and spanwise directions and the wallnormal extent of the ECS all increase monotonically with the increase of viscoelasticity, as is found in experiments. Examination of the parameter space (Re, Wi) in which ECS exist indicates that at least at the Reynolds number considered here, the transition behaviors from laminar to turbulent flow, from no drag reduction to drag reduction, and from moderate drag reduction to MDR can be connected to the birth, evolution and death of these ECS, respectively.In order to test the scenario that we infer from these results, we next implement direct numerical simulation (DNS), studying the transient and statistical...

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Turbulent drag reduction by polymer‐fiber mixtures

Cited by 11 publications

References 12 publications

Numerical simulation of turbulent drag reduction using rigid fibres

Numerical simulation of turbulent drag reduction using rigid fibres

Effect of Addition of Water-Soluble Polysaccharides on Bacterial Cellulose Production in a 50-L Airlift Reactor

Polymer induced drag reduction in exact coherent structures of plane Poiseuille flow

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