Design and Characterization of a Turbulence Chamber for Scalar Flux Measurements at a Sediment-Water Interface

A turbulence chamber designed specifically for the laboratory study of environmental scalar fluxes at sediment-water interfaces was developed and fully characterized. The turbulent flow field was documented using particle image velocimetry (PIV), with particular emphasis on turbulence characterization. The chamber is capable of reproducing a wide range of turbulence levels covering 6 orders of magnitude of the dissipation rate of turbulent kinetic energy (10-10-10-4m2s-3). Its performance range includes conditions similar to low energy environments such as lake and reservoir bottom boundary layers (BBLs), verified by comparison to field data. The chamber is forced by three peristaltic pumps plumbed to six equispaced orifices on the top cap of the chamber, forming a closed system. The pumps drive either a momentum source (a jet) in the vertical direction or a momentum sink. The pumps operate continuously, but randomly change direction to generate a horizontally homogeneous turbulent region near the sediment-water interface. Measured turbulence intensities show a quadratic relationship with pump speed (rpm), with typical environmental BBL turbulence intensities seen at low pump speeds (approximate to 10rpm). Dissipation shows a log-linear relationship to pump speed. A field experiment in Onondaga Lake was used to characterize typical lacustrine BBL turbulence, allowing the turbulence chamber design objective of reproducing the observed range of conditions to be met. The presented chamber design is adaptable and readily optimizable by users to the specific system under study. This flexible, self-contained design was motivated by the need to handle mercury-contaminated sediments from Onondaga Lake, the initial system it was used to study. Compared to similar facilities, the presented chamber provides well-characterized turbulence which is calibrated against environmental conditions with a direct correspondence between chamber and field turbulence levels in the form of turbulence intensity and turbulent dissipation values.