Author(s): W. S. J. Uijttewaal; G. H. Jirka
Linked Author(s):
Keywords: Shallow flows; Quasi two-dimensional turbulence; Experiments
Abstract: In this paper the results of experiments on shallow flow turbulence are presented. The shallowness of many flows in the natural environment affects its turbulence properties. Due to the vertical confinement large-scale structures with two-dimensional characteristics emerge. The consequences for transport of mass and momentum in such flows can be large and a proper prediction is therefore important. The essential features of shallow-flow turbulence are investigated in a relatively simple laboratory experiment. In a wide, straight shallow channel the flow is directed through a grid. Downstream of the grid the velocity components in the horizontal plane are measured using laser Doppler anemometry and particle image velocimetry. Depending on the parameter settings the turbulence induced by the grid exhibits quasi two-dimensional behaviour. Turbulence structures moving in the horizontal plane grow to a size much larger than the water depth. Energy-density spectra of the velocity components show two-dimensional characteristics for the large scales whereas the small-scale three-dimensional turbulence can be interpreted as an effective eddy viscosity acting on those large scale two-dimensional motions. The experimental data are of use for the development and validation of numerical models that are used in the practice of civil engineering and have to deal with the highly anisotropic turbulence properties as occurring in shallow flows.
Year: 2001