Author(s): Shinjiro Miyawaki; George Constantinescu; Gokhan Kirkil; Bruce Rhoads; Alexander Sukhodolov
Linked Author(s): Gokhan Kirkil, George Constantinescu
Keywords: No Keywords
Abstract: Detached Eddy Simulation (DES) is performed to investigate the 3-D flow dynamics and the role of the large-scale coherent structures at an asymmetrical river confluence with concordant bed. The mean flow predictions are validated using data from a field study. The geometry of the confluence induces strong flow convergence and large-scale secondary circulation. DES is conducted at field conditions (average channel Reynolds number is 160,000). DES accurately predicts most of the largescale features of the mean streamwise velocity distributions in cross-sections situated downstream of the junction. The present study demonstrates the important role played by the large-scale streamwise oriented vortices and associated helical motion in the momentum exchange processes between the two streams. It is shown the presence of these vortical cells on both sides of the shallow mixing layer developing downstream of the junction is responsible for some of the large-scale characteristics of the streamwise velocity distributions. DES results indicate that at the cross section within the scour hole downstream of the junction the streamwise-oriented vortical cell on the inner side of the mixing layer is larger and stronger than the one on the outer side of this layer. This effect is mainly due to the secondary circulation induced by the inner bank curvature and the realignment of the flow from the lateral tributaryas within the confluence region. The poor agreement of streamwise velocity distributions predicted by RANS with the field data is due to the underprediction of the strength of these cells of helical motion. Large-scale helical structures probably play an important role in shaping the bed in the downstream channel, as the bed friction velocity values beneath these cells are comparable to or higher than values below the mixing layer eddies.
Year: 2009