Search

The present study aims to understand the process of turbulent entrainment into a jet, as affected by background turbulence, using scalar statistics. Planar laser-induced fluorescence was employed to capture the orthogonal cross sections of the jet at a fixed downstream station with varying background turbulence intensities and length scales. The conditional scalar profiles revealed that the thickness of the scalar turbulent/turbulent interface is greater than that of the traditional turbulent/non-turbulent interface, and the interfacial thickness is an increasing function of the background turbulence intensity. Although nibbling remains the primary entrainment mechanism in the far field, increased occurrence of concentration "holes" within the interfacial layer in the presence of ambient turbulence suggests a more significant role of large-scale engulfment in the turbulent/turbulent entrainment process (although still below 1% of the total mass flux). Enhanced contribution of the area of detached jet patches (i.e., "islands") to that of the main jet is hypothesized to be evidence of intense detrainment events in the background turbulence. This can potentially contribute to a reduced net entrainment into the jet, which manifests as less negative values of scalar skewness within the jet core. [ABSTRACT FROM AUTHOR]

Planar laser-induced fluorescence is employed to investigate the concentration field in the developing region of a coaxial jet with an annular to inner jet velocity of one. Seeding the annular flow with a scalar shows that prior to the erosion of the inner scalar core, an inner interface exists, across which the scalar quantities exhibit sharp gradients akin to the traditional outer interface. Coarse grain filtering revealed that the outer interface establishes the universal fractal scaling before the onset of self-similarity, while the inner interface does not develop sufficient scale separation to do so due to the lack of shear. [ABSTRACT FROM AUTHOR]

Uganda's Vision 2040 aims to modernize rural water supply through a transition from community-managed point sources to professionally managed piped water services. At the start of the transition period, a learning alliance established in Kabarole District participated in action research to develop scenarios predicting possible future development trajectories. The diversity of its membership, whose formal institutional roles spanned national, district and niche levels, increased the robustness of the strategies proposed for the adaptively managed transition of the public water service. The learning alliance has been facilitated by a non-governmental organization providing funding and expert advice; the effectiveness of this approach is demonstrated. [ABSTRACT FROM AUTHOR]

We consider the scalar concentration field in the proximity of the turbulent/non-turbulent interface (TNTI) of a round momentum-driven turbulent jet at Re = 10 600. Orthogonal cross sections of the jet are taken at 50 nozzle diameters from the nozzle exit using planar laser-induced fluorescence. The conditional scalar concentration is evaluated along the interface-normal direction, identifying the thickness of the TNTI region as 0.64λ (where λ is the Taylor microscale). Conditioning the scalar concentration within the TNTI revealed higher values of the passive scalar in the vicinity of the boundary elements shaped by large vorticity structures, i.e., isosurface points with low curvature (flat regions), small interface angle, and large radial distance from the jet centerline. In contrast, small vorticity structures near the boundary manifesting with high interface curvature, high interface angle, and small radial distance are associated with lower concentration values. Using the current experimental resolution, we find that high concentrations near the far boundary points persist up to a distance of 0.40λ–0.48λ into the TNTI region, after which boundary points closer to the jet centerline exhibit larger concentration values along the interface-normal direction, similar to the fully turbulent region. The cross correlation analysis showed that in regions characterized by low streamwise momentum, there are positive, albeit small, scalar correlations between the non-turbulent and the TNTI regions. The latter may imply local detrainment of the fluid particles containing the scalar at far radial positions. [ABSTRACT FROM AUTHOR]

The impact of turbulent coflows on the dynamics of turbulent twin round jets is investigated experimentally. Parallel twin jets, at three jet spacing values and two Reynolds number/jet-to-coflow velocity ratios, were released into turbulent coflows with two distinct levels of turbulence intensity. Velocity measurements were made using acoustic Doppler velocimetry. An increase in the coflow turbulence intensity leads to an earlier merging and combining of the jets and also accelerates the rate of decay with downstream distance of the mean centerline excess velocity of the jets. The mean velocity on the symmetry line, for different values of jet spacing, ratios of jet exit velocity to coflow mean velocity, and coflow turbulence intensity, is self-similar when scaled by the maximum mean velocity on the symmetry line and the corresponding streamwise distance. Moreover, as the turbulence level of the coflow intensifies, the turbulence intensity along the symmetry line of the jets increases. The longitudinal integral length scale on the symmetry line of the twin jets decreases as the coflow turbulence intensity increases. The energy spectra of the coflowing twin jets show that the turbulence in the coflow transfers the energy contained by the larger scales to the smaller scales at a greater rate than that which occurs for jets in a quiescent background. However, as the jet spacing increases, less energy is transferred to the smaller scales. [ABSTRACT FROM AUTHOR]

Community-based projects play an important role in developing countries' efforts to meet the Millennium Development Goal of halving the population without access to improved water sources. Often associated with rural communities, they are increasingly being implemented in urban areas, where rural community-based management practices may be unsuitable. This research examines a small community-managed water supply scheme in Buea, a rapidly growing urban area in Cameroon. Stakeholder interviews and household questionnaires were used to better understand the implications of urbanization on community-managed water supply projects. The urban context adds management and planning pressures because of larger, more diverse, populations and rapid population growth. Urban community-managed schemes require an institutional framework to encourage participation, which is at an increased risk of failure due to the urban context. Finally, urban community-managed schemes need to be implemented in an institutional context, where they have legitimacy in the urban water supply framework, thereby allowing them to have access to the institutional and technical support they require to function sustainably. The consequence of failure is a return to ‘unimproved’ water sources. [ABSTRACT FROM PUBLISHER]

Engineers frequently use physical scale models of hydropower intakes to assess and minimize the occurrence of harmful free surface vortices. The impact of surface tension, viscosity and turbulence on the scaling behaviour of the vortices is examined here using an analytical free surface vortex model developed from measurements in a laboratory-scale hydropower intake. First, the effect of surface tension on the free surface depression is computed using a finite-difference model over a wide range of depression scales and shapes. The impact and scaling behaviour of surface tension are found to be qualitatively different depending on whether the depression is dimple- or funnel-shaped. The influence of viscosity on scaling predicted by the analytical vortex model contradicts trends recorded by previous authors, which suggests that additional processes such as turbulent diffusion may play a significant role at larger scales. Scale effects due to the interplay of viscosity and turbulence require further investigation, whereas those due to surface tension are fairly easily quantified and predicted. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Trinidad and Tobago's 1.3 million residents are provided water supply and sewerage services by a national utility whose service levels have been inadequate and deteriorating through the recent past, largely due to a lack of investment in utility infrastructure. A “willingness to pay” study assessed the degree of coverage and quality of service and the residents' willingness to accept water tariff increases for an increase in service level. Willingness to pay for change is low, below current tariffs, due to scepticism about the likelihood of change and due to the ability to cope with bad service through the pervasive use of local storage. [ABSTRACT FROM AUTHOR]

Wilson's disease (WD) is a hereditary disorder of copper metabolism, producing abnormally high levels of non-ceruloplasmin-bound copper, the determinant of the pathogenic process causing brain and hepatic damage and dysfunction. Although the disease is invariably fatal without medication, it is treatable and many of its adverse effects are reversible. Diagnosis is difficult due to the large range and severity of symptoms. A high index of suspicion is required as patients may have only a few of the many possible biomarkers. The genetic prevalence of ATP7B variants indicates higher rates in the population than are currently diagnosed. Treatments have evolved from chelators that reduce stored copper to zinc, which reduces the toxic levels of circulating non-ceruloplasmin-bound copper. Zinc induces intestinal metallothionein, which blocks copper absorption and increases excretion in the stools, resulting in an improvement in symptoms. Two meta-analyses and several large retrospective studies indicate that zinc is equally effective as chelators for the treatment of WD, with the advantages of a very low level of toxicity and only the minor side effect of gastric disturbance. Zinc is recommended as a first-line treatment for neurological presentations and is gaining acceptance for hepatic presentations. It is universally recommended for lifelong maintenance therapy and for presymptomatic WD. [ABSTRACT FROM AUTHOR]

The effect of approximately homogeneous isotropic turbulence on the dynamics of an axisymmetric turbulent jet (Re = 10 600 and 5800) in an ambient with a negligible mean flow is interpreted from the statistics of the passive scalar field. The ambient turbulence is generated by a random jet array and scalar concentrations are measured in orthogonal cross sections of the jet using planar laser-induced fluorescence. Statistics of the scalar field of the jet in a turbulent ambient are compared to those in a quiescent ambient, using classical Eulerian averages and those conditioned on the jet centroid. A two-region model for the jet structure in ambient turbulence is proposed based on the centroidal statistics. Following the developing region of the jet, the ambient turbulence disrupts the jet structure, due to modulation of the jet interface, meandering of the jet by large eddies, and entrainment of the turbulent ambient fluid, resulting in a faster concentration decay and reduced entrainment compared to the quiescent ambient. Further downstream, once the ambient turbulence has destroyed the jet, only molecular and turbulent diffusion modify the scalar concentrations. The regions' relative lengths depend primarily on the relative turbulence intensity (ξ) between the ambient and the jet, as assessed using centroidal analysis, which removes the effect of the relative length scale (l) on the jet behavior in the turbulent ambient. The centroidal scalar statistics reveal self-similarity and self-preservation in mean scalar properties before jet breakup, which occurs abruptly once ξ > 0.5. The smaller scales of ambient turbulence modulate the jet boundary and, when entrained, lead to a wider range of centerline concentrations and root mean square concentrations, which are hypothesized to increase local concentration gradients within the jet and reduce jet mixing. [ABSTRACT FROM AUTHOR]

Different driving algorithms for a large random jet array (RJA) were tested and their performance characterized by comparing the statistics of the turbulence generated downstream of the RJA. Of particular interest was the spatial configuration of the jets operating at any given instant (an aspect that has not been documented in previous RJAs studies), as well as the statistics of their respective on/off times. All algorithms generated flows with nonzero skewnesses of the velocity fluctuation normal to the plane of the RJA (identified as an inherent limitation of the system resulting from the unidirectional forcing imposed from only one side of the RJA), and slightly super-Gaussian kurtoses of the velocity fluctuations in all directions. It was observed that algorithms imposing spatial configurations generated the most isotropic flows; however, they suffered from high mean flows and low turbulent kinetic energies. The algorithm identified as RANDOM (also referred to as the "sunbathing algorithm") generated the flow that, on an overall basis, most closely approximated zero-mean-flow homogeneous isotropic turbulence, with variations in horizontal and vertical homogeneities of RMS velocities of no more than ±6 %, deviations from isotropy ( w/ u) in the range of 0.62-0.77, and mean flows on the order of 7 % of the RMS velocities (determined by averaging their absolute values over the three velocity components and three downstream distances). A relatively high turbulent Reynolds number ( Re = u ℓ/ ν = 2360, where ℓ is the integral length scale of the flow and u is a characteristic RMS velocity) was achieved using the RANDOM algorithm and the integral length scale ( ℓ = 11.5 cm) is the largest reported to date. The quality of the turbulence in our large facility demonstrates the ability of RJAs to be scaled-up and to be the laboratory system most capable of generating the largest quasi-homogeneous isotropic turbulent regions with zero mean flow. [ABSTRACT FROM AUTHOR]

A meshless method is used to simulate free-surface fluid flows containing solid particles, motivated by the need to simulate river ice dynamics problems. A smoothed particle hydrodynamics model (SPH), with an arbitrary Lagrangian–Eulerian formulation for the fluid phase, is two-way coupled with the discrete element method (DEM) for the solid phase. Validation test cases include a bouncing sphere on a level surface, a collapse of a granular column, wedge entry into still water and solids of different densities falling into still water. The computed results using the SPH-DEM model agree quantitatively with the expected behaviour in the test cases. Numerical convergence is demonstrated for the wedge entry validation case. The SPH-DEM model is then used to simulate the stability of floating ice blocks approaching a stationary cover and ice accumulation upstream of an obstruction. The results show promise to serve as a useful quantitative engineering tool. [ABSTRACT FROM PUBLISHER]

To 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 axisymmetric flows that corrects the RMS velocities to within the range of acceptable values is presented. Lastly, because the Doppler noise is thought to depend on the mean velocity, a series of laboratory experiments were undertaken to relate Doppler noise to the mean velocity. The results showed no clear relationship between the Doppler noise and the mean flow. In addition, subtracting the Doppler noise (measured for a given mean velocity) from the measured RMS velocities (at the same mean velocity) did not significantly decrease the RMS velocities. [ABSTRACT FROM AUTHOR]

Schemes to restore fish habitat in rivers often involve installing instream structures such as current deflectors to create and maintain riffle-pool sequences. However, there is a lack of field studies on the impact of these structures on flow dynamics and bed topography. The objective of this research is to characterize flow dynamics and sediment transport around paired deflectors used to enhance fish habitat in the Nicolet River, Quebec. Bed and bank topography surveys were taken with a total station, and velocity and bed shear stress estimates were obtained from an acoustic doppler velocimeter. Bedload sediment transport was assessed by two methods: tracer rocks (painted "particles" and passive integrated transponder tags) and sediment traps. Results show marked differences in bedload sediment transport patterns between the left bank and the right bank downstream of the deflectors. This is surprising considering that paired deflectors should produce a relatively symmetrical disruption to the flow field on each side. More high-flow dynamics data during overtopping conditions are required to understand the complex interactions between these instream structures and bedload transport. [ABSTRACT FROM AUTHOR]

The efficient use of water is necessary in water scarce regions like Barbados. This study provides an insight into the impact of two water demand management measures, water pricing and metering, on residential water use in Barbados. Econometric demand models of residential water use are developed to assess the potential of pricing policies to conserve water. The models are used as policy tools to investigate the impact of future increases in water price on water use and revenue generation, considering also the equity of price increases. Metering must be accompanied by a substantial increase in price to encourage water conservation. [ABSTRACT FROM AUTHOR]

A free-surface vortex is a mass of water rotating around an axis perpendicular to the free surface. It can occur when withdrawing water from reservoirs or rivers at hydropower intakes with low submergence. Existing vortex models provide general information about the symmetric vortex structure. The vortex structure occurring in an approach flow at the critical submergence condition is examined in detail. In the laboratory, a steady air-core vortex over a bottom intake was created in a wide recirculating flume, in which the water depth, mean velocity of the approach flow and intake discharge could be adjusted. Flow visualization shows that the approach flow results in a non-symmetrical velocity distribution in the vortex throughout the flow depth. The detailed set of high-speed particle image velocimetry data in a series of horizontal and vertical planes was used to observe the formation and evolution of the three-dimensional flow structure of the strong air-core vortex and determine the origin of the vortex. Analysis of these data revealed a complex three-dimensional vortex structure due to the approach flow interacting with the air-core vortex forming a secondary vortex originating at the mixing zone upstream of the vortex, identified by a zero downstream velocity component, and feeding into the upstream side of the intake. [ABSTRACT FROM AUTHOR]