Journal ArticleDOI
Numerical simulation of turbulent drag reduction using micro-bubbles
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In this paper, a series of numerical simulations of small spherical bubbles seeded in a turbulent channel flow at average volume fractions of up to 8% were performed and it was shown that even for relatively large bubbles, an initial transient drag reduction can occur as bubbles disperse into the flow.Abstract:
While turbulent drag reduction through the injection of micro-bubbles into a turbulent boundary layer is well established in experiments, there is a lack of corresponding supporting evidence from direct numerical simulations. Here we report on a series of numerical simulations of small bubbles seeded in a turbulent channel flow at average volume fractions of up to 8%. These results show that even for relatively large bubbles, an initial transient drag reduction can occur as bubbles disperse into the flow. Relatively small spherical bubbles will produce a sustained level of drag reduction over time.read more
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Direct Numerical Simulations of Gas-Liquid Multiphase Flows
TL;DR: In this paper, a review of the state-of-the-art numerical methods used for direct numerical simulations of multiphase flows, with a particular emphasis on methods that use the so-called "one-field" formulation of the governing equations, is presented.
Journal ArticleDOI
Friction Drag Reduction of External Flows with Bubble and Gas Injection
TL;DR: In this article, the use of partial and supercavities for drag reduction of axisymmetric objects moving within a liquid is reviewed, and the current applications of these techniques to underwater vehicles and surface ships are discussed.
Journal ArticleDOI
On the physical mechanisms of drag reduction in a spatially developing turbulent boundary layer laden with microbubbles
TL;DR: In this paper, the physical mechanisms responsible for the reduction of skin friction in a microbubble-laden spatially developing turbulent boundary layer over a flat plate are explained, and the location of peak Reynolds stress production is moved away from the wall to a zone of a smaller transverse gradient of the mean streamwise velocity.
Journal ArticleDOI
Bubble friction drag reduction in a high-Reynolds-number flat-plate turbulent boundary layer
TL;DR: In this article, the authors showed that at the lowest test speed and highest air injection rate, buoyancy pushed the air bubbles to the plate surface where they coalesced to form a nearly continuous gas film that persisted to the end of the plate with near-100% skin-friction drag reduction.
Journal ArticleDOI
The effect of bubbles on the wall drag in a turbulent channel flow
TL;DR: In this article, the effect of a few relatively large bubbles injected near the walls on the wall drag in the minimum turbulent channel was examined by direct numerical simulations, and the results showed that deformable bubbles can lead to significant reduction of the wall drifts by suppression of streamwise vorticity.
References
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Journal ArticleDOI
Equation of motion for a small rigid sphere in a nonuniform flow
Martin R. Maxey,James J. Riley +1 more
TL;DR: In this paper, the forces on a small rigid sphere in a nonuniform flow are considered from first prinicples in order to resolve the errors in Tchen's equation and the subsequent modified versions that have since appeared.
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Spectral/hp Element Methods for CFD
TL;DR: In this article, Jacobi polynomials Gauss-type integration Collocation differentiation Co discontinuous expansion bases are used to simulate incompressible flows in one-dimensional expansion bases.
Journal ArticleDOI
The Motion of High-Reynolds-Number Bubbles in Inhomogeneous Flows
Jacques Magnaudet,Ian Eames +1 more
TL;DR: In this article, a trident approach consisting of experimental, analytical, and numerical work has given a clearer description of the hydrodynamic forces experienced by isolated bubbles moving either in inviscid flows or in slightly viscous laminar flows, and a significant part of the paper is devoted to a discussion of drag, added mass force, and shear-induced lift experienced by spheroidal bubbles moving in inertially dominated, time-dependent, rotational, nonuniform flows.
Journal ArticleDOI
Drag reduction of a submersible hull by electrolysis
TL;DR: In this article, the authors show that the amount of drag reduction depends on the ratio of the mass flow of water in the wake to the time-rate of hydrogen mass produced beneath the boundary layer.