| 91 | 91 | Early 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. |
