Improvements in acoustic doppler velocimetery

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732Acoustic velocimeters have become popular for measuring turbulent and mean flows in fluid mechanics laboratories. A series of tests were conducted to evaluate the performance of several acoustic velocimeters at low signal to noise ratios (SNR) to assess the accuracy of mean flow estimates, and at typical SNR in response to tilting of the velocimeter head with respect to the flow. Tests were conducted in an open channel flow with Particle Imaging Velocimetery (PIV) measurements made for comparison and assessment of flow disturbance around the head. While limited in the scope of its assessment, this study shows large improvements have been made in the performance of acoustic velocimeters since their introduction in the early 1990s

Turbulence, instream wood and fish: ecohydraulic interactions under field conditions

This is the pre-peer reviewed version of the following article: Trinci, G, Harvey, GL, Henshaw, AJ, Bertoldi, W, Hölker, F. Turbulence, instream wood and fish: Ecohydraulic interactions under field conditions. Ecohydrology. 2020;e2211. https://doi.org/10.1002/eco.2211 , which has been published in final form at https://doi.org/10.1002/eco.2211. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions

Turbulence In Low Energy Lacustrine Environments At The Sediment-Water Interface

The sediment-water interface is an important region where biological, chemical, and physical processes occur. Fluid flow determines the ability of organisms to utilize the bottom sediments for food, shelter, and reproduction, the amount and rate of mass transfer between the sediment and bulk fluid, and the deposition, re-suspension and transport of sediment. Field experiments carried out in three medium sized basins, one a heavily polluted lake and the other two drinking water reservoirs, are used to describe typical turbulence levels during the mid to late stratified season (July through October) in a low energy lacustrine bottom boundary layer. Using these measurements, a turbulence chamber was developed for use in turbulent scalar flux studies. The chamber was characterized using particle image velocimetery (PIV), characterizing the near bed turbulence and dissipation levels. The chamber successfully reproduces the range of turbulent energy levels observed in the field, allowing a more direct comparison of results obtained in field and laboratory studies of scalar fluxes. Results from the two reservoirs were used in laboratory cohesive sediment erosion and resuspension tests of a mono-disperse kaolin clay and natural sediment cores obtained from various bottom and shore locations in one of the reservoirs. This testing showed the small bed stresses typical of the lacustrine bottom boundary layer were not sufficient to erode or resuspend significant quantities of sediment. Higher stress levels caused erosion and resuspension, but it was heterogeneous in nature and appeared to be tied to flow structures associated with the facility used to carry out the experiments. Even at higher stress levels, very short settling times (only 1-2 hours) were needed for observable erosion to occur. A method for estimating erosion utilizing images of the sediment-water interface and tracking the interface as an intensity peak over time was developed. Initial results show this is a reliable means to gauge the sediment-water interface position when optical access is available