Topic
Pipe flow
About: Pipe flow is a research topic. Over the lifetime, 13826 publications have been published within this topic receiving 351605 citations.
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TL;DR: In this paper, two simple feedback control laws for drag reduction were derived by applying a suboptimal control theory to a turbulent channel flow, which requires pressure or shear-stress information only at the wall.
Abstract: 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 Re τ = 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
193 citations
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TL;DR: A non-orthogonal helical co-ordinate system is introduced and it is found that both curvature and torsion induce non-negligible effects when the Reynolds number is less than about 40.
Abstract: A non-orthogonal helical co-ordinate system is introduced to study the effect of curvature and torsion on the flow in a helical pipe. It is found that both curvature and torsion induce non-negligible effects when the Reynolds number is less than about 40. When the Reynolds number is of order unity, torsion induces a secondary flow consisting of one single recirculating cell while curvature causes an increased flow rate. These effects are quite different from the two recirculating cells and decreased flow rate at high Reynolds numbers.
192 citations
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TL;DR: In this article, the authors quantify the delay in transition from laminar to turbulent flow caused by shear-thinning, suppression of turbulent fluctuations particularly in the radial and tangential components of normal stress, and the drag reduction at the higher Reynolds numbers.
Abstract: Measurements of mean axial velocity and of the three normal stresses have been obtained in fully developed pipe-flow with four concentrations of a polymer (sodium carboxymethyl cellulose) in aqueous solution and with water and viscous Newtonian fluids encompassing a range of Reynolds numbers from 240 to 111,000. The results quantify the delay in transition from laminar to turbulent flow caused by shear-thinning, the suppression of turbulent fluctuations particularly in the radial and tangential components of normal stress, and the drag reduction at the higher Reynolds numbers. They also confirm that the maximum drag reduction asymptote is appropriate to these shear-thinning solutions.
191 citations
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TL;DR: In this article, the authors used the lattice-Boltzmann scheme for the discretization of the Navier-Stokes equations of turbulent flows in a baffled stirred tank reactor.
191 citations
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TL;DR: In this article, a simplified model focusing particularly on the radial gas volume fraction distribution, the bubble size distribution and the radial residence of bubbles dependent on their size were determined for different distances from the gas injection.
191 citations