The rotating annular flume (RAF) is widely used to simulate the flow characteristics in rivers and lake environments. However, there is a secondary flow which cannot be eliminated but can be reduced by rotating the top and bottom rings of the flume in contrary directions. In this study, a physical model and a numerical model of RAF was used to study the optimal rotating ratio of the top ring to the flume channel. The numerical model was verified from the measured data. It was founded that the optimal rotating ratio obtained by the sand tracing experiment method is limited and the optimal rotating ratio is not fixed. For different experimental purposes, we need different rotating ratio of the RAF.
In earlier times the straight flume are commonly used in experiments of non-cohesive sediments such as sand and gravel. However, it is not suitable to study the transportation of the cohesive sediments because the cohesive sediments are usually transported in a flocculated form in which flocs are fragile and susceptible to break by the impellers of the recirculation pumps in the straight flume. Furthermore, the length of the straight flume is limited, so that the sediment eroded into suspension is lost and disappears at the end of the flume. Therefore, continuous supply of water and sediment during measurement are needed but it is not practical.
The rotating annular flume (RAF) can solve those problems. It consists of two components: a circular channel and a top ring that fits inside the channel. The flow is generated by moving the top ring or channel rather than the fluid. These are effectively infinitely long channels, in which there is no loss of water and sediment.