Laser Doppler Velocimetry Measurment of Turbulent Bubbly Channel Flow

1
Laser Doppler Velocimetry Measurment of
Turbulent Bubbly Channel Flow

• S. So, H. Morikita, S. Takagi, Y. Matsumoto
• Department of Mechanical Engineering, The
  University of Tokyo,
• 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
• Experiments in Fluids 33 (2002) 135-142

Shailesh Ozarkar MEE 771
2
Outline

• Experimental conditions and apparatus
• Measuring system
• Experimental results and discussion
• Single-phase flow
• Air-water bubbly flow
• Summary and conclusions

3
Experimental conditions

• Mono-dispersed 1-mm-diameter bubbles
• Experiments were conducted for three different
  bulk Reynolds number (1350,4100,8200)
• Average void fraction was in range 0.3 1.2
• Small amounts of surfactant (inhibit coalescence)

Table 1. Experimental conditions
4
Experimental apparatus
5
Measuring system

• Bubble size was measured using image-processing.
• LDV was used to measure liquid-phase velocity.
• Seeding particles spherical mono-disperse
  polystyrene particles of diameter.
• The terminal velocity
• Relaxation time
• Estimated Kolmogorov length scale
• 
  time scale
• Seeding particles have sufficiently high
  response.

6
Experimental results and discussion
Distribution of bubble diameters

• Without surfactant
• Average diameter and standard
• deviation
• 20 ppm of 3-pentanol (surfactant) was injected
  into the flow.
• With surfactant
• Average diameter and standard
• deviation

Fig. 4a, b. Photos of the bubbles in the test
section at Re8,200 and fg0.60 a without
pentanol b with pentanol
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Effect of surfactant on turbulence properties of
single-phase flow
Mean velocity profiles
Rms velocity fluctuations normalized by the wall
friction velocity
Fig. 5a, b. Comparisons between the experiment
results with/without 3-pentanol and the DNS
results (single-phase flow) Re 4100
8
Experimental results and discussion
Air-water bubbly flow
Fig. 6ac. Mean velocity profiles of the
liquid-phase flow
9
Experimental results and discussion
Air-water bubbly flow
Fig. 7ac. Streamwise rms velocity fluctuations
of the liquid-phase flow
10
Experimental results and discussion
Air-water bubbly flow
Mean velocity profiles under different Reynolds
numbers (void fraction of 0.6)
Rms velocity fluctuations with the variations in
Reynolds number (void fraction of 0.6)
Reynolds stress of liquid phase normalized by the
wall friction velocity (Re 4,100)
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Summary and conclusions

• In all cases there was strong preferential
  accumulation of bubbles near the wall.
• The mean velocity profile of liquid phase becomes
  steeper near wall and flattened around channel
  center.
• Streamwise turbulent intensity in the vicinity of
  wall was enhanced.
• Turbulent fluctuations and Reynolds stress in
  the liquid phase are very much suppressed around
  channel centre.