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TECHNICAL PAPERS

# Investigation of Microbubble Boundary Layer Using Particle Tracking Velocimetry

[+] Author and Article Information
Javier Ortiz-Villafuerte1

Department of Nuclear Engineering, Texas A&M University, College Station, TX 77843-3133

Yassin A Hassan2

Department of Nuclear Engineering, Texas A&M University, College Station, TX 77843-3133y-hassan@tamu.edu

www.pivchallenge.org

1

Currently at Department of Nuclear Systems, National Institute for Nuclear Research, Ocoyoacac, Mexico 52045.

2

Corresponding author.

J. Fluids Eng 128(3), 507-519 (Oct 11, 2005) (13 pages) doi:10.1115/1.2174062 History: Received March 31, 2004; Revised October 11, 2005

## Abstract

Particle tracking velocimetry has been used to measure the velocity fields of both continuous phase and dispersed microbubble phase, in a turbulent boundary layer, of a channel flow. Hydrogen and oxygen microbubbles were generated by electrolysis. The average size of the microbubbles was $15μm$ in radius. Drag reductions up to 40% were obtained, when the accumulation of microbubbles took place in a critical zone within the buffer layer. It is confirmed that a combination of concentration and distribution of microbubbles in the boundary layer can achieve high drag reduction values. Microbubble distribution across the boundary layer and their influence on the profile of the components of the liquid mean velocity vector are presented. The spanwise component of the mean vorticity field was inferred from the measured velocity fields. A decrease in the magnitude of the vorticity is found, leading to an increase of the viscous sublayer thickness. This behavior is similar to the observation of drag reduction by polymer and surfactant injection into liquid flows. The results obtained indicate that drag reduction by microbubble injection is not a simple consequence of density effects, but is an active and dynamic interaction between the turbulence structure in the buffer zone and the distribution of the microbubbles.

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## Figures

Figure 1

Sketch of the PIV setup

Figure 2

Typical image from a two phase boundary layer measurement

Figure 3

Overlay of the velocity vectors from 40 consecutive instantaneous fields, and final velocity profile after dividing the velocity field into multiregions for optimum tracking

Figure 4

Comparison of the mean velocity profile in the single phase boundary layer, using the three different methods shown to compute the wall friction velocity

Figure 5

Microbubble size distribution at a liquid velocity of 10mm∕s

Figure 6

Distribution of the freely moving microbubbles in the boundary layer, for five different drag reduction values

Figure 7

Modification of the profiles of the streamwise component of the liquid mean velocity vector across the two phase boundary layer, for five different drag reductions, in physical coordinates

Figure 8

Modification of the profiles of the streamwise component of the liquid mean velocity vector across the two phase boundary layer, for five different drag reductions, in wall coordinates

Figure 9

Modification of the profiles of the normal component of the liquid mean velocity vector across the two phase boundary layer, for the highest and lowest cases of drag reduction, in physical coordinates

Figure 10

z component of the mean vorticity field for the drag reduction of 10.1% case

Figure 11

z component of the mean vorticity field for the drag reduction of 27.5% case

Figure 12

z component of the mean vorticity field for the drag reduction of 41.9% case

## Errata

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