30

average of 25 readings from the water pressure transducer using the UP 34970A DAQ unit are recorded for each v, and each traverse positions near the floor. The resulting velocity profiles are shown in the plot in Figure 3-8. Large uncertainties are observed, particularly at high speeds and probe positions, because of vibration experienced by the probe due to the air-water interface.

    For both air and water streams, more accurate measurements like particle image velocimetry and Laser Doppler velocimetry are required to determine the basic flow pattern. The resulting velocity profiles can be used to develop analytical models of the air-water interface.



                       ----------- -------  -------  -------  -------0.8                  --TT I --0
           > 0.4

              0. 2

                01
                0         1       2        3        4        5        6
                Floor              Tunnel profile (inches)         Interface


  Figure 3-8 Velocity profiles (with uncertainty estimates) of water tunnel for velocity increasing from 0. 15 m/s to 0. 86 m/s in seven steps (corresponding to motor input voltage increasing from I V to 8 V in steps of I V). Table 3-2 summarizes the results of the velocity profile measurements for the water tunnel. The mean, maximum absolute deviation and standard deviations are tabulated as with the air measurements. The maximum absolute deviation is found to fluctuate