Abstract
Grid turbulence is one of most fundamental turbulence phenomena because it dose not have a velocity distribution in the main flow. This paper describes the computations of grid turbulence in shallow flows in open channels. Since the shallow grid turbulence is bounded by a solid bottom and a free surface, its fundamental turbulence structures are completely different from the three-dimensional grid turbulence. The vertical confinement of the flow suppresses the three-dimensionality and attains strongly two-dimensional features with inverse cascade of turbulence energy from small scale toward large-scale structures due to vortex merging. 2D depth averaged models and 3D models with linear and non-linear constitutive equations are applied to a shallow grid turbulence and the results are discussed through the comparison with the results of laboratory tests performed by Uijttewaal and Jirka (2003). In 2D computations, a modified non-linear 0-equation model could capture the fundamental aspects of flow phenomena including inverse cascading. In 3D models, an artificial disturbance at inlet boundary is necessary to generate inverse cascade.
