A Fluid perspective on fish passage design and performanc

Turbulence is omnipresent in natural and man-made environments, having a range of impacts on the biota in aquatic systems, from positive to detrimental to neutral. Lessons learned from fish habitats choices and fish swimming are applied to the context of fish passage to look at the importance of turbulence on design and performance. Past studies have shown a strong correlation between fish performance and physical parameters. While a wide range of parameters (biological and physical) with various length and time scales are important in determining success of fish passage, we will focus on determining physical parameters responsible for the challenges fish encountered in fish passage structures and the type of measurements needed to refine the design of these structures. New developments such as selective fish passage will also be explored. A deeper understanding of the biology and physics, better numerical models and new sensor technology allow us to dream about new and exciting advances in fishways design and performance evaluation

A review of recent developments on turbulent entrainment in stratified flows

Stratified interfaces are present in many geophysical flow situations, and transport across such an interface is an essential factor for correctly evaluating the physical processes taking place at many spatial and temporal scales in such flows. In order to accurately evaluate vertical and lateral transport occurring when a turbulent flow impinges on a stratified interface, the turbulent entrainment and vorticity generation mechanisms near the interface must be understood and quantified. Laboratory experiments were performed for three flow configurations: a vertical thermal, a sloping gravity current and a vertical turbulent jet with various tilt angles and precession speeds. All three flows impinged on an interface separating a two-layer stably stratified environment. The entrainment rate is quantified for each flow using laser-induced fluorescence and compared to predictions of Cotel and Breidenthal (1997 Appl. Sci. Res. 57 349–66). The possible applications of transport across stratified interfaces include the contribution of hydrothermal plumes to the global ocean energy budget, turbidity currents on the ocean floor, the design of lake de-stratification systems, modeling gas leaks from storage reservoirs, weather forecasting and global climate change.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85428/1/2010_T142_014044.pd

Turbulence inside a vortex: Take two

In this paper, a modified theory based on earlier work on stratified entrainment is proposed to explain the persistence of trailing vortices in the far field. These vortices grow at a laminar rate even though the Reynolds number is high and in the turbulent regime. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71242/2/PHFLE6-14-8-2933-1.pd

Development, testing and demonstration of a portable submersible miniature particle imaging velocimetry device

A portable underwater particle image velocimetry (PIV) device has been developed, tested and demonstrated. The underwater PIV uses a 532 nm battery-powered 90 mW continuous laser. The laser beam is pulsed via a camera-synchronized chopper wheel. Images were recorded using a 1 megapixel black and white 10-bit CCD battery-powered camera controlled via a PCMCIA frame grabber card connected to a laptop computer. The system was validated against a standard laboratory PIV for average velocities up to 15 cm s−1 downstream from a 1.6 cm circular cylinder. The average vorticities calculated between the two systems were similar with a maximum difference of 3.6%. The average velocities were also similar with the largest difference occurring at the slowest flow recorded (difference of 0.5 cm s−1), resulting in a 9.4% difference. The maximum eddy size was comparable between the two systems with an average error of 4%. The system was field tested in the Huron River, Michigan downstream from a 1.2 cm diameter submerged limb. Mean velocities and standard deviations were comparable to acoustic Doppler velocimeter data. This paper presents the first published subsurface PIV data from a fluvial environment, demonstrating potential applications for a number of ecological and geomorphological studies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58132/2/mst7_8_031.pd

Characterization of the Impingement Dynamics of Pulsed Rocket Plumes with the Ground at Low Ambient Pressure

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76629/1/AIAA-2007-5707-681.pd

Temperature and velocity measurements of a rising thermal plume

Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 16 (2015): 579–599, doi:10.1002/2014GC005576.The three-dimensional velocity and temperature fields surrounding an isolated thermal plume in a fluid with temperature-dependent viscosity are measured using Particle-Image Velocimetry and thermochromatic liquid crystals, respectively. The experimental conditions are relevant to a plume rising through the mantle. It is shown that while the velocity and the isotherm surrounding the plume can be used to visualize the plume, they do not reveal the finer details of its structure. However, by computing the Finite-Time Lyapunov Exponent fields from the velocity measurements, the material lines of the flow can be found, which clearly identify the shape of the plume head and characterize the behavior of the flow along the plume stem. It is shown that the vast majority of the material in the plume head has undergone significant stretching and originates from a wide region very low in the fluid domain, which is proposed as a contributing factor to the small-scale isotopic variability observed in ocean-island basalt regions. Lastly, the Finite-Time Lyapunov Exponent fields are used to calculate the steady state rise velocity of the thermal plume, which is found to scale linearly with the Rayleigh number, in contrast to some previous work. The possible cause and the significance of these conflicting results are discussed, and it is suggested that the scaling relationship may be affected by the temperature-dependence of the fluid viscosity in the current work.This work was funded by the National Science Foundation (grant EAR-055199) and the MAPS Dean's Office at UCL.2015-09-0

Constraining the source of mantle plumes

© The Author(s), 2016. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Earth and Planetary Science Letters 453 (2016): 55-63, doi:10.1016/j.epsl.2015.12.008.In order to link the geochemical signature of hot spot basalts to Earth’s deep interior, it is first necessary to understand how plumes sample different regions of the mantle. Here, we investigate the relative amounts of deep and shallow mantle material that are entrained by an ascending plume and constrain its source region. The plumes are generated in a viscous syrup using an isolated heater for a range of Rayleigh numbers. The velocity fields are measured using stereoscopic Particle-Image Velocimetry, and the concept of the ‘vortex ring bubble’ is used to provide an objective definition of the plume geometry. Using this plume geometry, the plume composition can be analysed in terms of the proportion of material that has been entrained from different depths. We show that the plume composition can be well described using a simple empirical relationship, which depends only on a single parameter, the sampling coefficient, Sc. High-Sc plumes are composed of material which originated from very deep in the fluid domain, while low-Sc plumes contain material entrained from a range of depths. The analysis is also used to show that the geometry of the plume can be described using a similarity solution, in agreement with previous studies. Finally, numerical simulations are used to vary both the Rayleigh number and viscosity contrast independently. The simulations allow us to predict the value of the sampling coefficient for mantle plumes; we find that as a plume reaches the lithosphere, 90% of its composition has been derived from the lowermost 260−750 km in the mantle, and negligible amounts are derived from the shallow half of the lower mantle. This result implies that isotope geochemistry cannot provide direct information about this un-sampled region, and that the various known geochemical reservoirs must lie in the deepest few hundred kilometres of the mantle.This work was funded by the National Science Foundation (grant EAR-055199), the MAPS Dean’s Office at UCL and the CIDER workshop (EAR-1135452).2016-12-2

A Case Study of Laser Wind Sensor Performance Validation by Comparison to an Existing Gage

A case study concerning validation of wind speed measurements made by a laser wind sensor mounted on a 190 square foot floating platform in Muskegon Lake through comparison with measurements made by pre-existing cup anemometers mounted on a met tower on the shore line is presented. The comparison strategy is to examine the difference in measurements over time using the paired-t statistical method to identify intervals when the measurements were equivalent and to provide explanatory information for the intervals when the measurements were not equivalent. The data was partitioned into three sets: not windy (average wind speed measured by the cup anemometers ≤ 6.7m/s) windy but no enhanced turbulence (average wind speed measured by the cup anemometers \u3e 6.7m/s), and windy with enhanced turbulence associated with storm periods. For the not windy data set, the difference in the average wind speeds was equal in absolute value to the precision of the gages and not statistically significant. Similar results were obtained for the windy with no enhanced turbulence data set and the average difference was not statistically significant (α=0.01). The windy with enhanced turbulence data set showed significant differences between the buoy mounted laser wind sensor and the on-shore mast mounted cup anemometers. The sign of the average difference depended on the direction of the winds. Overall, validation evidence is obtained in the absence of enhanced turbulence. In addition, differences in wind speed during enhanced turbulence were isolated in time, studied and explained

Laser Wind Sensor Performance Validation with an Existing Gage

A new approach to laser wind sensor measurement validation is described and demonstrated. The new approach relies on the paired-t statistical method to generate a time series of differences between two sets of measurements. This series of differences is studied to help identify and explain time intervals of operationally significant differences, which is not possible with the traditional approach of relying on the squared coefficient of variation as the primary metric. The new approach includes estimating a confidence interval for the mean difference and establishing a level of meaningful difference for the mean difference, and partitioning the data set based on wind speed. To demonstrate the utility of the new approach, measurements made by a laser wind sensor mounted on a floating buoy are compared first with those made by a second laser wind sensor mounted on a nearby small island for which the co-efficient of variation is high (\u3e 99%). It was found that time intervals when high differences in wind speed occurred corresponded to high differences in wind direction supporting a hypothesis that the two laser wind sensor units are not always observing the same wind resource. Furthermore, the average difference for the 100m range gate is positive, statistically significant (α=0.01) and slightly larger than the precision of the gages, 0.1m/s. One possible cause of this difference is that the surface roughness over land is slowing the wind at 100m slightly. A second comparison was made with previously existing cup anemometers mounted on a metrological mast located on-shore. The cup anemometers are about 8m lower than the center of the lowest range gate on the laser wind sensor. The data was partitioned into three sets: not windy (average wind speed at the cup anemometers ≤ 6.7m/s) windy but no enhanced turbulence (average wind speed at the cup anemometers \u3e 6.7m/s), and windy with enhanced turbulence. Periods of enhanced turbulence are associated with the passage of a cold frontal boundary. The paired-t analysis for the not windy data set showed a difference in the average wind speeds of -0.096m/s, less in absolute value than the precision of the gages. The negative sign indicates slower wind speed over land as well as at a lower height, which is expected. Similar results were obtained for the windy with no enhanced turbulence data set. In addition, the average difference was not statistically significant (α=0.01). The windy with enhanced turbulence data set showed significant differences between the buoy mounted laser wind sensor and the on-shore mast mounted cup anemometers. The sign of the average difference depended on the direction of the winds in the periods of enhanced turbulence. Mean turbulent kinetic energy was measured to be greater when air flow into Muskegon Lake was predominantly from over land versus when air flow was predominantly from Lake Michigan. The higher mean turbulent kinetic energy for flow originating over land would likely be due to greater surface roughness experienced by the overland flow. Overall, the value of the new approach in obtaining validation evidence has been demonstrated. In this case, validation evidence is obtained in periods of no enhanced turbulence. Differences in wind speed during periods of enhanced turbulence are isolated in time, studied and are correlated in time with differences in wind direction