Particle Image Velocimetry (PIV) and pressure measurement techniques were
performed to investigate the drag reduction due to microbubble injection in the boundary
layer of a fully developed turbulent channel flow. Two-dimensional full-field velocity
components in streamwise-near-wall normal plane of a turbulent channel flow at
Reynolds number of 5128 based on the half height of the channel were measured. The
influence of the presence of microbubbles in the boundary layer was assessed and
compared with single phase channel flow characteristics. A drag reduction of 38.4% was
achieved with void fraction of 4.9%.
The measurements were analyzed by studying the turbulence characteristics utilizing
wavelet techniques. The wavelet cross-correlation and auto-correlation maps with and
without microbubbles were studied and compared. The two-dimensional and threedimensional
wavelet maps were used to interpret the results.
The following observations were deduced from this study:
1. The microbubble injection within the boundary layer increases the turbulent
energy of the streamwise velocity components of the large scale (large eddy size, low
frequency) range and decreases the energy of the small scale (small eddy size, high
frequency) range.
2. The wavelet cross-correlation maps of the normal velocities indicate that the
microbubble presence decrease the turbulent energy of normal velocity components for
both the large scale (large eddy size, low frequency) and the small scale (small eddy size,
high frequency) ranges.
3. The wavelet auto-correlation maps of streamwise velocity shows that the
intensities at low frequency range were increased with microbubble presence and the
intensities at high frequency range were decreased.
4. The turbulent intensities for the normal fluctuating velocities at both low
frequency and high frequency range were decreased with microbubble injection.
This study presents the modifications in the characteristics of the boundary layer of
channel flow which are attributed to the presence of microbubbles. Drag reduction
studies with microbubble injections utilizing wavelet techniques are promising and are
needed to understand the drag reduction phenomena.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/3200 |
| Date | 12 April 2006 |
| Creators | Zhen, Ling |
| Contributors | Hassan, Yassin A. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 8092090 bytes, electronic, application/pdf, born digital |
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