ADV Measures Water Velocity Profiles Induced by Air Diffusers and Mixers*

An Acoustic Doppler Velocimeter (ADV) was used to collect water-velocity profiles in two water bodies during 1995-97. The U.S. Geological Survey (USGS) collected the data as part of a study with the U.S. Army Corps of Engineers (Corps) to aid in the verification and calibration of a 3-dimensional hydrodynamic model known as MAC-3D. Pilot-scale tests in a large tank, and field-scale tests in a reservoir, were conducted to determine the mixing patterns associated with various configurations of coarse-bubble air diffusers and mechanical mixers.

The pilot-scale tests were conducted in a test tank (Figure 1) at the Corps’ Waterways Experiment Station (WES) in Vicksburg, Mississippi, in a cylindrical tank at water depths ranging from about 3 to 10 m. Field-scale tests were done at Egan Quarry (Figure 2), a 14-m deep lake adjacent to the John E. Egan Water Reclamation Plant, operated by the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) in Schaumburg, Illinois. The data were collected during operation of coarse-bubble air diffusers, submersible mixers, and surface mixers.

The ADV used at both WES and Egan Quarry measures three-dimensional water velocities using a 10-MHz acoustic signal that measures flow in a 0.25 cm³ sampling point. The ADV measures at 25 Hz, or 25 times per second, and can measure velocities to +/- 2.5 m/s, and has a velocity resolution of 0.1 mm/s. Because the ADV measures velocity at a single point, the ADV was placed at several different depths to collect a complete profile of water velocities (from top to bottom in the water column).

The ADV used in this study was equipped with an internal compass and pitch/roll sensor. In the tank tests, these options were not used because of the magnetic interference introduced by the steel tank, so a mount was built that kept the ADV motionless during measurements and allowed the ADV to be moved both radially and vertically in the tank between measurements. This allowed reliable three-dimensional water velocities to be measured at different radial distances and water depths in the tank and reported in terms of x, y, and z coordinates.

For the Egan Quarry tests, the compass and tilt/roll sensor were used and velocities were reported in terms of east-west, north-south, and vertical components. The ADV was lowered vertically to the desired measurement depth on a moored cable from a stationary boat. This allowed three-dimensional water velocity measurements to be taken anywhere in the quarry. Figure 3 shows water velocity profiles during Test eg973S, which were taken 6.1 meters west (top graph) and 32 meters west (bottom graph) of the submersible mixer at Egan Quarry during the summer of 1997.

Figure 3. Velocity Profiles from Egan Quarry

*Material for this article is courtesy of Gary P. Johnson of the USGS. All data are provisional and subject to revision.

• ADV