There are four annular flumes, modeled after one at Delft University of Technology in the Netherlands. These flumes are ideal for long-term, replicated experiments on the effects of flow on biological and chemical processes, ecosystem processes and sediment transport or distribution studies. Each of the four annular flumes has an outside diameter of 399 cm and a cross-channel width of 30 cm. The flume area is approximately 18,095 cm2. The maximum water depth is 40 cm. The volume of the flume with a 20-cm water depth is 362 liters. As for the racetrack flume, the annular flumes are constructed of seawater-resistant materials. The floors are PVC. The sidewalls are constructed of optical quality glass, with the exception of two flat acrylic panels spaced around the circumference. These acrylic panels facilitate access of measurement sensors and sampling devices to the interior of the flume, which otherwise is nearly completely enclosed by a titanium plate mounted to the PVC top which drives the flow. The titanium plate serves as a heat exchanger (maintaining desired temperatures in the range of 10-20 oC with a precision of ± 0.3 oC).
The flow is driven by rotation of the titanium top plate and the simultaneous counter-rotation of the main flume channel. This counter-rotation minimizes the cross-channel (radial, or v component) flow caused by water moving continuously in a circle. Flow speeds ranging from 0 to 74 cm sec-1 (mid-water column) have been achieved. The annular flumes can be programmed to run various flow speeds for different periods of time and also to reverse the direction of flow. This capability enables experiments where flow reversal is important (e.g., mimic tidal flows).
Flow characteristics are measured with a 2-axis laser Doppler velocimeter (LDV) mounted on a 2-axis traverse to measure the flow fields throughout the water column at a given location along the circumference of the flume. The 2-axis LDV measures flow speeds in the horizontal (tangential) and vertical directions. Radial (cross-stream) velocity can be derived based of the continuity equation for incompressible flow.
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