Impacts of desalination plant discharges on the marine environment: A critical review of published studies

Planar laser-induced fluorescence (PLIF) is a non-intrusive technique for measuring scalar concentrations in fluid flows. A fluorescent dye is used as a scalar proxy, and local fluorescence caused by excitation from a thin laser sheet can be related to dye concentration. This review covers quantitative PLIF in aqueous flows, with discussions of fluorescence theory, experimental methods and equipment, image processing and calibration, and applications of the technique.

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Planar laser induced fluorescence in aqueous flows

In a laboratory study, we quantified the temporal energy flux associated with the degeneration of basin-scale internal waves in closed basins. The system is two-layer stratified and subjected to a single forcing event creating available potential energy at time zero. A downscale energy transfer was observed from the wind-forced basin-scale motions to the turbulent motions, where energy was lost due to high-frequency internal wave breaking along sloping topography. Under moderate forcing conditions, steepening of nonlinear basin-scale wave components was found to produce a high-frequency solitary wave packet that contained as much as 20% of the available potential energy introduced by the initial condition. The characteristic lengthscale of a particular solitary wave was less than the characteristic slope length, leading to wave breaking along the sloping boundary. The ratio of the steepening timescale required for the evolution of the solitary waves to the travel time until the waves shoaled controlled their development and degeneration within the domain. The energy loss along the slope, the mixing efficiency, and the breaker type were modeled using appropriate forms of an internal Iribarren number, defined as the ratio of the boundary slope to the wave slope (amplitude/wavelength). This parameter allows generalization to the oceanographic context. Analysis of field data shows the portion of the internal wave spectrum for lakes, between motions at the basin and buoyancy scales, to be composed of progressive waves: both weakly nonlinear waves (sinusoidal profile with frequencies near 10 24 Hz) and strongly nonlinear waves (hyperbolic‐secant-squared profile with frequencies near 10 23 Hz). The results suggest that a periodically forced system may sustain a quasi-steady flux of 20% of the potential energy introduced by the surface wind stress to the benthic boundary layer at the depth of the pycnocline.

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The degeneration of internal waves in lakes with sloping topography

Experiments were performed using laser-induced fluorescence (LIF) and a microconductivity probe on turbulent dense jets inclined upwards at an angle of 60° into stationary environments. Such jets are frequently used to discharge industrial wastewaters. Time-averaged LIF images show concentration profiles that vary smoothly in space but instantaneous images show considerable patchiness. Dilution at the jet impact point was found to be higher than previously reported. Downstream from the impact point, the flow becomes predominantly horizontal with a complex additional mixing process that results in ultimate dilutions considerably higher than the impact dilution. The flow is highly turbulent in the vicinity of the falling jet with large concentration fluctuations. These fluctuations decay with distance due to turbulence collapse under the influence of density stratification. The end of the mixing zone is defined as the location where the intensity of the concentration fluctuations falls to 0.05 (i.e. 5%) of ...

Mixing in Inclined Dense Jets

The characteristics of chemical odor plumes released into a turbulent open channel flow are evaluated in the context of chemical plume tracking. The objective is to assess the availability and usefulness of chemosensory cues to animals, such as benthic crustaceans, attempting to orient in the plume. Releasing fluorescent dye into the fully developed turbulent boundary layer of a large laboratory-scale flume created turbulent odor plumes. Flow visualization of odor fields created with varying release velocity, release distance from the bed, and nozzle diameter indicated that chemosensory cues in plumes depend on the release characteristics as well as the ambient flow conditions. Thus, to understand animal behavior, it is important to quantify the plume release properties and characteristics. We chose to quantify concentration fields for the case of isokinetic release using the planar laser-induced fluorescence technique. These measurements indicate that the time-averaged concentration converges far too slowly to be useful to a foraging animal. Similarly, resolving the rise slope of a concentration burst requires sampling rates unattainable by animals, and the spatial variation of rise slope is too mild to follow without lengthy sampling periods. In addition, only mild variation with distance from the source is observed in the concentration burst magnitude and duration. Thus, the time-averaged concentration, rise slope, and burst shape all appear to have limited usefulness for plume orientation for animals known to orient effectively to these types of odor sources.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.2001.46.5.1034

Adrian Ferrier

Papers

Mixing in Inclined Dense Jets

Application of optical techniques to the study of plumes in stratified fluids

Discussion and Closure: Mixing in Inclined Dense Jets

Closure to “Mixing in Inclined Dense Jets” by Philip J. W. Roberts, Adrian Ferrier, and Greg Daviero