Characterization of a Bubble Curtain for PIV Measurements - Selected Topics of Computational and Experimental Fluid Mechanics - page 258

Fig. 9 Left bubble density against pressure for three holes, compared with the results of one hole.
Right oscillation frequency of the waves compared with the frequency of the bubbles
4.3 Results Obtained When Waves Were Introduced
The right side of Fig. 8 shows speeds of bubbles in the upward direction at a pressure
of 15.6 cmHg, when controlled waves with different frequencies were introduced
in the flume. The speed remains close to 25 cm/s, which indicates that the average
ascending velocity of the bubbles is maintained.
The air pressure is controlled and the flow is steady. The left panel of Fig. 9
shows that the particle density generated by each hole is retained even with all holes
uncovered.
The periods of the waves produced were compared with the periods measured
from the bubbles. The results are depicted in the right panel of Fig. 9 . It can be seen
that the frequency of the bubbles matches the frequency of the waves.
5 Conclusions
The results show that bubbles are able to trace the flow behavior. Their horizontal
variation has a well defined period. The amplitude of oscillation increases as the
bubble rises. Measurements can be made in an area where both phenomena are
small and can be easily taken into account. The upward velocity of the bubbles was
not affected when waves with frequencies above 0.5Hz were created. However, for
waves of longer period the slower motion between peaks and valleys provide almost
a 10% difference.