Flow and bubble statistics of turbulent bubble-laden downflow channel. (May 2020)

• Record Type: Journal Article
• Authors: Cifani, P.; Kuerten, J.G.M.; Geurts, B.J.
• Is Part Of: International journal of multiphase flow. Volume 126(2020)
• Publication Date: 2020-05
• Subjects: Bubbly flow -- Turbulent channel flow -- DNS -- Bubble statistics -- Kinetic energy spectra; Multiphase flow -- Periodicals; Écoulement polyphasique -- Périodiques; Multiphase flow; Periodicals; 620.1064
• DOI: 10.1016/j.ijmultiphaseflow.2020.103244
• Languages: English
• ISSNs: 0301-9322

Abstract

Highlights: Fully resolved turbulent channel flow (Re = 6300) for number of bubbles up to O(1000). Liquid statistics increase homogeneity of the bulk flow with the gas volume fraction. Found short separation bubble clustering independently of the gas volume fraction. Pdf of the bubble velocity fluctuations was found to be approximately Gaussian. Kinetic energy spectrum did not show a marked −3 scaling. Abstract: Direct numerical simulations of fully developed turbulent channel downflow at bulk Re equal to 6300, loaded with monodisperse bubbles at gas volume fractions α = 0.5 %, α = 2.5 % and α = 10 % have been carried out. Bubble deformability, surface tension, as well as discontinuity in the material properties across the bubble interfaces are explicitly accounted for. A full-scale channel of size 4 πH × 2 H × 4 πH /3 in terms of the channel half-width H containing a number of bubbles up to O ( 10 3 ) is considered. The statistical structure of the bubbles, the probability density function describing the bubble velocity and the liquid kinetic energy spectra have been determined. A close range preferential clustering of the bubbles was found with a maximum density independent of the gas volume fraction at a separation distance of about 2.2 R, with R the bubble radius. Preferential horizontal alignment and a general tendency to repulsion is shown for separation distances smaller than 3 R . At larger separation distances a close to random distribution is observed for α = 2.5 % and α = 10 %, while tendency to vertical alignment is observed for α = 0.5 % . The pdf of the bubble velocity fluctuations was found to be well approximated by a Gaussian distribution. The liquid kinetic energy spectra in the channel core do not show a marked − 3 scaling, which was previously reported for homogeneous isotropic turbulence and pseudo-turbulence.