Susan Gaskin

The Basin of Mexico Hydrogeological Database (BMHDB): Implementation, queries and interaction with open source software

Integrated Water Management at the Basin level is a concept that was introduced in the 1990s and is a goal in every national and local water management plan. Unfortunately this goal has not been achieved mainly due to a lack of both tools and data management, as data must be gathered from different sources and in different formats. Compounding this problem is the fact that in some regions different water agencies are in charge of water supply as is the case in the Basin of Mexico, in which Mexico City and its Metropolitan Zone are located. The inhabitants of the Basin of Mexico, which comprises five different political entities and in which different agencies are in charge of water supply rely on the Basins aquifer system as its main water supply source. However, a regional hydrogeological database in this area does not exist which is why the use of both a Relational Database Management System (RDMBS) and a Geographic Information System (GIS) is proposed in order to improve regional data management in the study area. Data stored in this new database, the Basin of Mexico Hydrogeological Database (BMHDB) comprise data on climatological, borehole and run-off variables, readily providing information for the development of hydrogeological models. A simple example is used to show how geostatistical analysis can be done using the data directly from the BMHDB. The structure of the BMHDB allows easy maintenance and updating, representing a valuable tool for the development of regional studies.

Characteristics of Free Surface Vortices at Low-Head Hydropower Intakes

AbstractTools for engineers who assess and optimize hydropower intakes are provided to help them measure and quantify the characteristics of free surface vortices (characteristic radius, bulk circulation, tip depth, nominal depression slope) that form at the intakes. Accessible methods are proposed for measuring and modelling vortex characteristics and the processes that affect their generation and strength. Common mechanisms that produce and strengthen the vortices (flow separation, shear, asymmetric approach flow) are discussed. An analytical model, based on Burgers’s vortex model and laboratory measurements, is described that incorporates the effect of the approach flow and intake geometry on vortex characteristics. Simple measurement techniques (acoustic Doppler velocimetry and surface particle tracking velocimetry) are presented by which the flow and vortex characteristics can be documented, allowing the model to be adjusted to the particularities of the specific intake under consideration. The analy...

The effect of background turbulence on jet entrainment: an experimental study of a plane jet in a shallow coflow

Many effluents are released into water bodies or into the atmosphere, and dilution is relied on to minimize the toxic effects of the pollutants on the environment. Dilution occurs due to entrainment and subsequent mixing of the “clean” (or cleaner) ambient fluid and the effluent stream. In the near field, dilution occurs due to momentum or buoyancy driven entrainment into the effluent stream, which is proportional to a characteristic velocity of the jet or plume. Whereas in the far field, dilution occurs due to turbulent diffusion at a rate dependent on the level of turbulence in the receiving fluid. In order to predict the expected dilution of an effluent stream, it is necessary to answer the question, at what point does the dilution mechanism change and how does it affect dilution rates. An experimental study examining the velocity and concentration decay of plane jets released into shallow coflows with increasing levels of external turbulence, indicated that levels of external turbulence just large enough to disrupt the jet structure reduced dilution rates significantly. This indicates that models, in which the jet dilution and turbulent diffusion are superimposed, will not always give a conservative estimate of effluent dilution.

Noise in Turbulence Measurements Using Acoustic Doppler Velocimetry

AbstractTo validate the use of acoustic Doppler velocimeters (ADVs) for the measurement of turbulent flows, experiments were conducted in an axisymmetric turbulent jet and in approximately homogenous isotropic turbulence with zero mean flow. The jet experiments show that the horizontal RMS velocities measured by the ADV were overestimated when compared to both flying hot-film anemometry measurements and the accepted values in the literature. However, the vertical component of the RMS velocity agrees well with those of other studies. This was furthermore confirmed by the ADV measurements in the isotropic turbulence with zero mean flow. Given that the overestimated RMS velocities in the horizontal directions may be caused by Doppler noise and spikes, two postprocessing filters and a Doppler noise–reduction method were applied to the jet data in an attempt to correct the data. Although the RMS velocities decreased, they remained erroneously higher than the accepted values. A noise-reduction method for axisym...

Free surface intake vortices: theoretical model and measurements

ABSTRACT Axially stretched free-surface vortices occur at low-head hydropower intakes under specific flow and geometric conditions. When they are sufficiently strong, they can harm performance or cause premature failure of mechanical components such as turbine blades or guide vanes. Laboratory-scale experimental models are currently used to assess the risk of vortex formation during the design phase, but uncertainty remains as to how vortex characteristics translate from the laboratory scale to the much larger scale of an actual hydropower plant. This paper proposes a semi-empirical model that roughly predicts how the approach flow and intake geometry determine the key vortex characteristics (the core radius, bulk circulation and the depth of the free surface depression). The model is developed using detailed velocity measurements of the approach flow and the flow inside the vortex in a laboratory-scale physical model, using analytical models and insights drawn from previous work.

A study of a buoyant axisymmetric jet in a small co-flow

This paper deals with measurements of and an integral model for a buoyant axisymmetric jet in a very small co-flow. The integral model is based on the insights gained from the measurements presented here and other recent experiments, which suggest that the turbulent flow is simply advected and the entrainment is that normal for a jet or plume in a still ambient fluid. General equations for the turbulent flow trajectories are also developed. The predictions of the theory are verilied for the no cross-flow case and the cases where the jet or plume is ejected vertically or horizontally into a very small cross-flow. The results of experiments in which a buoyant jet is released in the same direction as the horizontal ambient flow, show that outside the turbulent region the entrainment velocities can be represented with uniform flow and the appropriate sink. Direct measurement of the strength of the sink allows the transition from weakly- to strongly-advected behaviour to be determined. The departure of the trajectory measurements from the theory also provides information about the transition. The transition location is then compared with recent measurements in which the jets and plumes are ejected vertically into a very small cross-flow.

The axisymmetric and the plane jet in a coflow

The approximate variation of the mean properties in an axisymmetric jet and a two dimensional jet with an ambient coflow in an infinite duct have been determined using the excess momentum equation and an entrainment function. The turbulent velocity flux, consisting of a portion due to the excess jet velocity and a portion due to the turbulent coflow velocity, is carried by a velocity approximately equal to the top hat velocity. The entrainment into this flow is driven by the excess jet velocity and the entrainment function varies to allow for the change in entrainment from the strong jet to the weak jet. The entrainment constant is determined from the data of Nickels and Perry [14] for the axisymmetric case and the data of Bradbury and Riley [6] for the two dimensional case. All coflow experiments are in ducts and the effect of the duct is explored for the axisymmetric case. This paper is a prelude to the study of a buoyant jet in a coflow and a buoyant jet in a crossflow.

Modelling the long-term evolution of worst-case Arctic oil spills

We present worst-case assessments of contamination in sea ice and surface waters resulting from hypothetical well blowout oil spills at ten sites in the Arctic Ocean basin. Spill extents are estimated by considering Eulerian passive tracers in the surface ocean of the MITgcm (a hydrostatic, coupled ice-ocean model). Oil in sea ice, and contamination resulting from melting of oiled ice, is tracked using an offline Lagrangian scheme. Spills are initialized on November 1st 1980-2010 and tracked for one year. An average spill was transported 1100km and potentially affected 1.1 million km2. The direction and magnitude of simulated oil trajectories are consistent with known large-scale current and sea ice circulation patterns, and trajectories frequently cross international boundaries. The simulated trajectories of oil in sea ice match observed ice drift trajectories well. During the winter oil transport by drifting sea ice is more significant than transport with surface currents.

Differential diffusion of high-Schmidt-number passive scalars in a turbulent jet

The separate evolution, or differential diffusion, of high-Schmidt-number passive scalars in a turbulent jet is studied experimentally. The two scalars under consideration are disodium fluorescein (Sc≡ ν/D = 2000) and sulforhodamine 101 (Sc= 5000). The objectives of the research are twofold: to determine (i) the Reynolds-numberdependence, and (ii) the radial distribution of differential diffusion effects in the selfsimilar region of the jet. Punctual laser-induced fluorescence (LIF) measurements were obtained 50 jet diameters downstream of the nozzle exit for five Reynolds numbers (Re ≡ uod/ν = 900, 2100, 4300, 6700 and 10 600, where u0 is the jet exit velocity, d is the jet diameter, and ν is the kinematic viscosity) and for radial positions extending from the centreline to the edges of the jet cross-section (0 r/d 7.5). Statistics of the normalized concentration difference, Z, were used to quantify the differential diffusion. The latter were found to decay slowly with increasing Reynolds number, with the root mean square of Z scaling as Zrms ≡� Z 2 � 1/2 ∝ Re −0.1 , (or alternatively � Z 2 �∝ Re −0.2 ). Regardless of Reynolds number, differential diffusion effects were found to increase away from the centreline. The increase in differential diffusion effects with radial position, along with their increase with decreasing Reynolds number, support the hypothesis of increased differential diffusion at interfaces between the jet and ambient fluids. Power spectral densities of Z were also studied. These spectra decreased with increasing wavenumber – an observation attributed to the decay of the scalar fluctuations in a turbulent jet. Furthermore, these spectra showed that significant differential diffusion effects persist at scales larger than the Kolmogorov scale, even for moderately high Reynolds numbers.

Ecosystem biomimetics for resource use optimization in buildings

An ecomimetic method is developed as an innovative and transdisciplinary design approach rooted in the field of biomimetics. This new method emulates the interrelated complexity of the parts of an ecosystem with the intent to design buildings that are more efficient, effective and holistic. Ecomimetics refers to the design of buildings that mimic ecosystem processes and functions. This approach provides potential opportunities for climate change adaptation and mitigation by optimizing the use of resources in buildings. One challenge to the application of ecomimetics in architecture is the lack of systematic methods supported by scientific research, which may prevent development in this field. A theoretical basis and the initial development of an ecomimetic design method is presented, with a description of each step of the design process. Ecological systems are selected for functional properties that match architectural design goals, and then design tools are used to abstract and transfer those properties to architectural systems. The design tools integrated in the method are from the fields of ecological engineering, systems dynamics and architecture. The case of the Eastgate Center in Harare, Zimbabwe, is used to illustrate the method.