Modeling Natural Hydrodynamic Systems with a Differential-Turbulence Column

Abstract

A differential-turbulence column (DTC) has been designed to simulate hydrodynamic and chemical processes associated with pollutant fate in aquatic environments. The reactor uses five vertically spaced oscillating grids to simulate turbulence in natural hydrodynamic systems. Measurements of hydrodynamic and chemical reactions can be obtained from supporting instruments. The homogeneous turbulent kinetic energy (TKE) field produced by the DTC when all grids operated identically was compared to established grid-stirred systems. Detailed mapping of the turbulence structure indicated that the system obeys standard scaling relations for grid-stirred turbulence and produces homogeneous, isotropic turbulence. The apparatus was used to simulate TKE and sediment-loading profiles for open-channel flow (OCF) and homogeneous turbulence. Through the appropriate selection of grid stroke and frequency, the apparatus can be made to mimic the exponential-decay law associated with turbulence intensity in OCF systems. Under homogeneous and OCF turbulent conditions, sediment profiles obtained in the DTC accurately followed conventional theory. These experiments suggest that a DTC reactor can be designed to quantitatively simulate turbulence intensity and sediment loading associated with aquatic systems.