抄録
The laser doppler velocimeter (LDV) using an optical fiber probe is advantageous to avoid hydraulic interactions between a bubble and the probe, compared with other probe-based methods. The typical response of the LDV probe was investigated by measuring the velocity of an air plug rising in water in a vertical pipe (I.D. 10 mm). Measured data was compared with the air plug velocity measured from VTR images taken at 13500 frame/s. The doppler signal analysis by using the Wavelet-transformation clearly indicated that the measured velocity tended to decrease steeply as the bubble came into contact with the probe, after showing a constant velocity. This finding indicates that it is necessary to discard the data obtained in the proximity of the probe in order to obtain the true velocity.
