Advanced Post-Processing and Correlation Analyses in High-Velocity Air-Water Flows. 2- Microscopic Properties

The on-going interest in air-water flows is accompanied sometimes by citations of outdated articles and some ignorance of key contributions. A basic issue is the inadequate, incomplete interpretation of air-water flow instrumentation by hydraulic engineers and researchers. This article focus on the bubbly flow structure of high-velocity air-water flow based upon measurements by means of intrusive phase detection probes. It is shown that some advanced post-processing techniques may yield expanded information on the air-water structures and particle clustering

Turbulence Characterisation of High-Velocity Free-Surface Flows

In high-velocity free-surface flows, air is continuously being trapped and released through the free-surface. Such high-velocity highly-aerated flows cannot be studied numerically because of the large number of relevant equations and parameters. Herein an advanced signal processing of traditional single- and dual-tip conductivity probes provides some new information on the air-water turbulent time and length scales. The technique is applied to turbulent open channel flows in a large-size facility. The auto- and cross-correlation analyses yield some characterisation of the large eddies advecting the bubbles. The transverse integral turbulent length and time scales are related to the step height: i.e., Lxy/h ~ 0.02 to 0.2, and T.sqrt(g/h) ~ 0.004 to 0.04. The results are irrespective of the Reynolds numbers. The present findings emphasise that turbulent dissipation by large-scale vortices is a significant process in the intermediate zone between the spray and bubbly flow regions (0.3 < C < 0.7). Some self-similar relationships were observed systematically at both macroscopic and microscopic levels. The results are significant because they provide a picture general enough to be used to characterise the air-water flow field in prototype spillways

Air-Water Time and Length Scales in Skimming Flows on a Stepped Spillway: Application to the Spray Characterisation

Modern stepped spillways are typically designed for large discharge capacities corresponding to a skimming flow regime. Skimming flows are characterised by large amounts of entrained air and very-strong interactions between main stream turbulence, step cavity recirculation and free-surface. The present study is focused on new measurements of air-water turbulent time and length scales in air-water flow using several phase-detection intrusive probes. A new signal processing method and some correlation analyses were developed and applied. The air water flow properties presented basic characteristics that were qualitatively and quantitatively comparable to previous studies in skimming flows. Some self-similarity was observed systematically at both macroscopic and microscopic levels. This included the distributions of void fraction, bubble count rate, interfacial velocity and turbulence level at a macroscopic scale, and the bubble/droplet chord distributions, and the auto- and cross-correlation functions at a microscopic level. Self-similarity is closely linked with dynamic similarity, and present results demonstrated a number of self-similar relationships that remain invariant under changes of scale which led in turn to remarkable application at prototype scales. The present findings are significant because they provide a picture general enough to be used as a first approximation to characterise the air-water flow field in similar stepped spillway structures. The correlation analyses yielded a characterisation of the large eddies advecting the bubbles. The basic results included the transverse and streamwise integral turbulent length scales, the transverse and streamwise integral turbulent time scales, and the advection length scale. The turbulent length scales characterised a measure of the size of large vortical structures advecting air bubbles in the skimming flows. Both streamwise and transverse air-water length scales were closely related to the characteristic air-water depth Y90 : i.e., Lxy/Y90 = 0.05 to 0.2. The result was irrespective of the Reynolds numbers within the range of the experiments. Detailed measurements in the spray region highlighted the existence of an upper spray region for C > 0.95 to 0.97. In this upper spray, the distributions of droplet chord sizes and the distributions of advection length scales presented some marked difference with the rest of the flow. It is suggested that this highlighted a change in spray structure, where the upper spray region consisted primarily of ejected droplets interacting little with the rest of the flow until they re-attached

Meeting the challenges of the waste hierarchy: A performance evaluation of EU countries

The focus of this paper is to evaluate how well European countries are advancing towards a Circular Economy transition and to which extent they are fulfilling the European Union (EU) requirements in terms of municipal waste management. With this aim, an innovative composite indicator is devised by integrating the Goal Programming Synthetic Indicator (GPSI) methodology with the Analytic Hierarchy Process (AHP). The suggested methodology allows to encompass not only the guidelines provided by the EU directives and the EU Waste Hierarchy, but also the deviations from the EU thresholds. As a first step of the analysis, a dashboard of indicators is identified together with a set of targets that European countries are supposed to meet. Indicators, targets and their relative importance in the dashboard have been discussed and validated by a team of experts. Then, two Goal Programming Synthetic Indicators are computed taking into account two different perspectives. The first one rewards the countries with good performance in the higher level of the Waste Hierarchy, while the second one penalizes countries whose infringements are in the lower part of the Waste Hierarchy. Hence two different systems of aggregating weights are identified by means of the Analytic Hierarchy Process and accordingly two scenarios are explored. The analysis is performed using Eurostat data on 28 European countries from 2013 to 2018. For each year, countries are assessed in terms of their ability to keep the right waste management track delineated by the Waste Hierarchy principles. Countries’ ranking over time is first obtained and then interpreted in light of countries policies and achievements, deriving policy suggestions to improve waste management strategy able to reach the expected results

Environmental sustainability and service quality beyond economic and financial indicators: A performance evaluation of Italian water utilities

As water utilities operate as natural monopolists and they provide essential services for human life, their activities are regulated by public authorities. The sustainable use of water resources and a specific attention on social needs should be essential goals for this kind of firms, so that the evaluation of their business should go beyond their profitability and their financial solvency. Keeping pace with the new Circular Economy paradigm and the evolution of the water regulatory framework, in this paper we suggest a global composite indicator apt to evaluate in a novel way the water utilities performance, encompassing financial and economic indexes together with environmental sustainability and service quality measures. To show its empirical implementation we evaluate the performance of Italian water utilities. The operating context is also under scrutiny focusing on specific water utility features such as size, geographical location, degree of diversification and ownership. In this light, operating in the Center and being large are considered favourable background conditions, while the South and the medium size display a significant unfavourable influence on the water utility performance. Multi-utilities are more advantaged with respect to the mono-utilities and no significant distinction can be made among the different ownership models. ispartof: Socio-Economic Planning Sciences status: Published onlin

Water pollution in wastewater treatment plants: An efficiency analysis with undesirable output

The environmental efficiency of 96 Tuscan (Italian) wastewater treatment plants (WWTPs) is investigated taking into account the quality of the outgoing water in terms of pollutant. In this regard, the presence of the residual nitrogen in the outgoing treated water is considered as undesirable output. The efficiency analysis is performed by applying a novel integrated Analytic Hierarchy Process/Non-radial Directional Distance Function (AHP/NDDF) approach, combining the benefits of the two techniques. Similarly to the standard NDDF approach, the suggested model allows to include simultaneously inputs, desirable and undesirable outputs and not to overestimate the efficiency scores. At the same time, the AHP inclusion gives the possibility to directly take into account the decision maker preferences in the weighting system and to encompass some existing directional distance function models as special cases.The obtained results are then used to identify the efficiency explanatory variables: among them, the facilities' capacity, the percentage of wastewater discharged by the industrial and agricultural activities and the level of compliance with the pollutant concentration threshold set by the legislator have a significant impact on the WWTP performance. The integrated performance assessment allows the water authorities to combine the WWTP efficiency together with the environmental sustainability issue and it has the potential for further promising environmental inspections

Advanced Post-Processing and Correlation Analyses in High-Velocity Air-Water Flows

The interest in air-water flows has not diminished in recent years, but it is accompanied by frequent citations of early, sometimes outdated articles. A basic issue is the inadequate, incomplete interpretation of air-water flow instrumentation by hydraulic engineers and researchers. This article comments on high-velocity air-water flow measurements by means of intrusive phase detection probes. This article focus on the bubbly flow structure of high-velocity air-water flow based upon measurements by means of intrusive phase detection probes. It is shown that some advanced post-processing techniques may yields expanded information on the air-water turbulent flow properties and bubbly flow structures. The outcomes demonstrate simple techniques in high-velocity air-water flow analysis

Joint Observation of the Galactic Center with MAGIC and CTA-LST-1

MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes (IACTs), designed to detect very-high-energy gamma rays, and is operating in stereoscopic mode since 2009 at the Observatorio del Roque de Los Muchachos in La Palma, Spain. In 2018, the prototype IACT of the Large-Sized Telescope (LST-1) for the Cherenkov Telescope Array, a next-generation ground-based gamma-ray observatory, was inaugurated at the same site, at a distance of approximately 100 meters from the MAGIC telescopes. Using joint observations between MAGIC and LST-1, we developed a dedicated analysis pipeline and established the threefold telescope system via software, achieving the highest sensitivity in the northern hemisphere. Based on this enhanced performance, MAGIC and LST-1 have been jointly and regularly observing the Galactic Center, a region of paramount importance and complexity for IACTs. In particular, the gamma-ray emission from the dynamical center of the Milky Way is under debate. Although previous measurements suggested that a supermassive black hole Sagittarius A* plays a primary role, its radiation mechanism remains unclear, mainly due to limited angular resolution and sensitivity. The enhanced sensitivity in our novel approach is thus expected to provide new insights into the question. We here present the current status of the data analysis for the Galactic Center joint MAGIC and LST-1 observations

An experimental study of air-water skimming flow properties on a stepped spillway

In questa tesi è presentato uno studio sperimentale sulle proprietà aria-acqua delle correnti areate (skimming flow). L’indagine sperimentale è stata svolta presso “The University of Queensland” a Brisbane, Australia sotto la revisione del Prof. Hubert Chanson. E’ stato utilizzata una scala di stramazzi di un metro di larghezza e pendenza costante di 22°. Per varie ed elevate portate, tipiche di un regime di skimming flow, sono state indagate le proprietà macroscopiche e microscopiche della corrente utilizzando sonde intrusive in grado di rilevare le 2 fasi (aria-acqua). Successivamente sono stati analizzati ed elaborati i dati attraverso il metodo della correlazione. Le proprietà del fluido acqua-aria, sia qualitativamente che quantitativamente, hanno mostrato caratteristiche di base simili ai precedenti studi sulle correnti areate ed hanno messo in luce alcune autosimilitudini. Queste sono state osservate sistematicamente a livello sia macroscopico che microscopico. A livello macroscopico è stata analizzata la distribuzione della frazione di vuoto, della frequenza di conteggio delle bolle, della velocità interfacciale e del livello di turbolenza. A livello microscopico, si è posta l’attenzione sulla distribuzione della dimensione delle bolle/gocce e sui risultati ottenuti dall’analisi dell’ auto- correlazione e della correlazione

Turbulence characteristics in skimming flows on stepped spillways

The stepped spillway design is characterised by some increase in the rate of energy dissipation on the chute associated with a reduction of the size of the downstream energy dissipation system. This study presents a thorough investigation of the air-water flow properties in skimming flows with a focus on the turbulent characteristics. New measurements were conducted in a large-size facility (theta = 22 degrees, h = 0.1 m) with several phase-detection intrusive probes. Correlation analyses were applied to estimate the integral turbulent length and time scales. The skimming flow properties presented some basic characteristics that were qualitatively and quantitatively in agreement with previous air-water flow measurements in skimming flows. Present measurements showed some relatively good correlation between turbulence intensities Tu, and turbulent length and time scales. They illustrated large turbulence levels and large turbulent time and length scales in the intermediate region between the spray and bubbly flow regions