Changes between Version 195 and Version 196 of WikiStart

Oct 18, 2016, 11:31:17 AM (4 years ago)



  • WikiStart

    v195 v196  
    9090'''Profiling Acoustic Doppler Velocimetry (ADV)'''
    9191Early experiments used 3 co-mounted Nortek Vectrino Profiler Acoustic Doppler Velocimetry (ADV) probes ADVs for mapping three-dimensional flow velocities, whilst later experiments including the main experiments used 2 ADVs to minimize side lobe interference, and because of the loss of one probe. The ADVs were run at 100Hz in all experiments, both in the initial tests and in the actual experiments. The ADV probes measure three component velocities over a depth range of around 30 mm (up to 34 mm), with this zone starting 40 mm below the probe head. Bottom tracking by the instruments enables this depth to be precisely known and controlled, provided sufficient seeding is present in the flow. ADV collection was fully synchronised with the traverse through sending of the required voltage offset signal to them, thus enabling individual velocity files to be collected for each probe at each traverse. Movement of these probes on the traverse in the y and z planes allows detailed vertical profiles and flow mapping to be undertaken. Initial test experiments used the 3 probes, 1 was a stem probe with additional shielding, and 2 were flexible probes. The basal probe was numbered 1, middle 2, and upper probe 3, and were at heights of 7.2, 10 and 13 cm respectively. Lateral offset in the x-direction was 8.5 cm between probes 1 (most downstream probe) and 2, and 7.5 cm between probes 2 and 3 (most upstream). The traverse positions for each cross-section were based on probe 2 being positioned directly above the cross-section. These 3 probes were co-mounted on the traverse in order to collectively measure over a height of approximately 6 cm. ADV dwell times varied between 30 and 60 seconds.
    92 [[BR]]
    9395In the actual data collection experiments, two ADV probes were used. The basal probe is numbered 1, and the upper probe is numbered 3 [keeping with the earlier experimental protocol]. The traverse positions are based on the position of ADV1, the basal and most downstream ADV. The offset in the x-direction is 11 cm between probe 1 (most downstream probe) and probe 3 (most upstream) [i.e. when the traverse is positioned in the zero position (56 cm upstream of the end of the straight channel section) then ADV1 is in the zero position, and ADV3 is at -11 cm]. The dwell time at each point is 60 seconds. In the initial position the ADVs start 15 cm from the sidewall. Note that in these experiments the conductivity probe is located 7.3 cm downstream from ADV1, and is offset by 5.5 cm such that its initial position is 20.5 cm from the wall. The ADVs are positioned at the following positions from the floor: