Observational and numerical methods for quantifying and modeling of turbulence in a stratified reservoir

Abstract

The interplay between stratification and shear in lakes controls the vertical mixing, which is the mostimportant mechanism affecting the transport of heat, salt, momentum and suspended and dissolvedsubstances. This study attempts to quantify and characterize the turbulence from direct measurementsconducted in a reservoir. A 3D numerical model is used to investigate the water column hydrodynamics forthe duration of measurements and the performance of various turbulence models used in the CFD model areinvestigated via simulation of mixing in the reservoir. The drawdown curves produced by the turbulencemodels are formulized through linear equations. Although, use of different turbulence models do not havesignificant effects on the flow hydrodynamics away from the intake structure; significant effects especially onturbulence kinetic energy production are observed at the orifice. Therefore, for simulation of withdrawalflow, either use of shear stress transport (SST) k-omega models solving equations all the way to the wall or kepsilonmodels with the nonequilibrium wall function is recommended to account for the changes in thepressure gradient. In this study, the methods using quantified turbulent characteristics of the flow toreformulate the Stokes' settling velocity to be applied in turbulent flows are also investigated. An approach topredict setting velocity in turbulent flows that utilizes acoustic Doppler instruments for quantification ofturbulent characteristics is presented. Modification of the Stokes' settling velocity with thenondimensionalized turbulent kinetic energy production profiles lead better results than other turbulencecharacteristics (buoyancy flux and by Richardson number flux) widely used in characterizing turbulentmixing.