Author(s): Jianmin Ma; J. J. R. Williams
Linked Author(s): John J.R. Williams
Keywords: Large coherent structures; Large Eddy Simulation; Open-channel flow
Abstract: Large Eddy Simulation (LES) is carried out to investigate the large scale coherent structures in the open channel flow. The rough bed is represented by a hexagonal arrangement of spheres, with a diameter of a quarter of flow depth. We perform the simulation with two computational boxes of different sizes; one is four times of the other. The coherent structures are composed of quasistreamwise and asymmetric hairpin vortices, which are visualised by Q method. The development of the large structures due to the increase of domain is clearly observed. The arrangement of the structures in the large box is more complex than in the small box. In the streamwise direction, the structures are connected to be longer ones; whilst in the spanwise direction, the width of parallel structures keeps constant. The contributions of the large structures to Reynolds Stress (RS) and Turbulent Kinetic Energy (TKE) are explored. The difference between two boxes suggests that the size of the computational domain does determine the development of coherent structures and thus the physical properties of the flow field.
Year: 2010