Effects of Aeration on the Performance of an ADV

Using acoustic Doppler velocity meters (ADV's) to collect field data can be hampered by the air-water flow mixtures that are often present in and around the vicinity of many hydraulic structures. The flow fields near weirs, spillways, gate structures, fish screens, fish ladders, pumping plants and powerplants are just a few examples where significant air entrainment can and does occur. ADV manufacturers warn their users of the detrimental effects of attempting measurements in bubbly flows. However, no significant data exists for evaluating how much air is too much or what the relative drop in accuracy is with increase in air concentration. Experience using the probes has shown that air bubbles in the flow causes a drop in the reported correlation value and general increases in noise level. A simple study evaluating the effect of air concentration on ADV performance was conducted in Reclamation's Water Resources Research Laboratory (WRRL). In the study, a porous stone attached to a compressed air supply was used to generate bubbles in a channel of flowing water. Simultaneous measurements by the ADV probe and an air concentration probe were collected. Data were collected for a single velocity and variable air concentration. ADV performance was evaluated using standard parameters reported by the ADV during the measurement process.