3D Flow Velocity Pattern in a Circular Section Within River Reach: An Experimental Study

Circular sections utilize vortex flow within the chamber to separate sediment particles from the river flow. The structure of flow inside the circular basins is complicated and fully three-dimensional. In this paper, three-dimensional flow velocity was measured to understand the flow structure and to distinguish secondary currents above and below a deflector which was installed inside the basin. Within the vortex extractor, the variation of sediment concentration is greatly affected by variation in the velocity components, in vertical, radial and tangential directions of flow inside the basin. The three-dimensional flow velocity was measured using an Acoustic Doppler Velocity meter. The velocity of flow was measured at 448 different nodal points, at eight different layers within the flow depth. Of these 448 nodal points, 336 nodal points were below the deflector and 112 nodal points were above it. The measurements were taken at eight different degrees. From this study, it was found that the tangential velocity under a deflector decreases, compared to the tangential velocity in a vortex basin without a deflector, and as a result the secondary currents under a deflector also decrease. Furthermore, as the secondary currents under a deflector decrease, these currents approach the central orifice. Secondary currents under a deflector are useful to impinge deposited sediment particles towards the flushing orifice.