Changes between Version 181 and Version 182 of WikiStart

Oct 17, 2016, 5:22:25 PM (7 years ago)



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    9090'''Profiling Acoustic Doppler Velocimetry (ADV)'''
    9191Two profiling Acoustic Doppler probes will be used for mapping three-component flow velocities within the channel. These probes come in two types, 1 is a stem probe with additional shielding, and one is a flexible probe that allows closer deployment. Both 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. These probes are co-mounted on the traverse in order to collectively measure over a height of approximately 6 cm. Movement of these probes on the traverse in the y and z planes allows detailed vertical profiles and flow mapping to be undertaken. The dwell time at each point is 60 seconds. The basal probe is numbered 1, and the upper probe is 2, and are at heights of xx, and yy cm respectively. Lateral offset in the x-direction is ?? cm between probe 1 (most downstream probe) and 2. The traverse positions for each cross-section are based on probe 2 being positioned directly above the cross-section. ADV collection is 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.
     93'''Siphon rig'''
     94The siphon rig consists of 12 siphon tubes, each with a nominal internal diameter of 1.6 mm (3.2. mm external diameter), and 15 m in length. The siphons are held in place by a plastic holder which is in turn connected to a rod attached to the channel. The siphon rig is positioned 80 mm downstream of the inflection downstream of bend 2, offset laterally 78 mm off-axis from the position of the UVP (on the right hand side as looking downstream). The siphons are positioned at heights of 10, 25, 50, 75, 100, 125, 150, 175, 200, 250, 350 and 450 mm above the bed. The siphon tubes are connected to a 12 head peristaltic pump. Samples are taken when the traverse (with ADVs and conductivity probe) is positioned upstream measuring the straight section. Samples are collected in an array of 12 plastic containers over a 60 second period, starting at 5, 10, 15, 20, 25, 30 and 35 minutes into the experiment (the start of the experiment is defined as that point where the input is steady). Samples are subsequently measured for conductivity using an Anton Paar DMA35 Portable Density Meter.