TY - JOUR

T1 - Flow and bubble statistics of turbulent bubble-laden downflow channel

AU - Cifani, P.

AU - Kuerten, J. G.M.

AU - Geurts, B. J.

PY - 2020/5

Y1 - 2020/5

N2 - 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 4πH × 2H × 4πH/3 in terms of the channel half-width H containing a number of bubbles up to O(103) 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 2.2R, with R the bubble radius. Preferential horizontal alignment and a general tendency to repulsion is shown for separation distances smaller than 3R. 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.

AB - 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 4πH × 2H × 4πH/3 in terms of the channel half-width H containing a number of bubbles up to O(103) 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 2.2R, with R the bubble radius. Preferential horizontal alignment and a general tendency to repulsion is shown for separation distances smaller than 3R. 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.

KW - Bubble statistics

KW - Bubbly flow

KW - DNS

KW - Kinetic energy spectra

KW - Turbulent channel flow

UR - http://www.scopus.com/inward/record.url?scp=85079840649&partnerID=8YFLogxK

U2 - 10.1016/j.ijmultiphaseflow.2020.103244

DO - 10.1016/j.ijmultiphaseflow.2020.103244

M3 - Article

AN - SCOPUS:85079840649

VL - 126

JO - International Journal of Multiphase Flow

JF - International Journal of Multiphase Flow

SN - 0301-9322

M1 - 103244

ER -