A numerical and experimental study was carried out for validation of a previously proposed design criterion for a cross-flow turbine and a new semi-empirical formula linking inlet velocity to inlet pressure. An experimental test stand was designed to conduct a series of experiments and to measure the efficiency of the turbine designed based on the proposed criterion. The experimental efficiency was compared to that from numerical simulations performed using a RANS model with a shear stress transport (SST) turbulence closure. The proposed semi-empirical velocity formula was also validated against the numerical solutions for cross-flow turbines with different geometries and boundary conditions. The results confirmed the previous hydrodynamic analysis and thus can be employed in the design of the cross-flow turbines as well as for reducing the number of simulations needed to optimize the turbine geometry.

In the last few years, some regions of the Mediterranean area have witnessed a progressive increase in extreme events, such as urban and flash floods, as a response to the increasingly frequent and severe extreme rainfall events, which are often exacerbated by the ever-growing urbanization. In such a context, the urban drainage systems may not be sufficient to convey the rainwater, thus increasing the risk deriving from the occurrence of such events. This study focuses on a particularly intense urban flood that occurred in Palermo (Italy) on 15 July 2020; it represents a typical pluvial flood due to extreme rainfall on a complex urban area that many cities have experienced in recent years, especially in the Mediterranean region. A conceptual hydrological model and a 2D hydraulic model, particularly suitable for simulations in a very complex urban context, have been used to simulate the event. Results have been qualitatively validated by means of crowdsourced information and satellite images. The experience of Palermo, which has highlighted the urgent need for a shift in the way stormwater in urban settlements is managed, can be assumed to be a paradigm for modeling pluvial floods in complex urban areas under extreme rainfall conditions. Although the approaches and the related policies cannot be identical for all cities, the modeling framework used here to assess the impacts of the event under study and some conclusive remarks could be easily transferred to other, different urban contexts.

The potential energy of the water in Water Distribution Networks (WDNs) usually exceeds the amount needed for delivery and consumption and, at the present time, it is mainly dissipated through Pressure Reducing Valves (PRVs) or Open Water Tanks. The present study suggests the use of a new energy-producing device, a Cross-flow turbine with positive outlet pressure named PRS (Power Recovery System), which can provide the same service as PRVs and water tanks, with additional significant hydropower production. After a short presentation of the PRS, the management rules of the proposed device are laid out, according to two possible modes. In the ‘passive’ mode, the piezometric level downstream of the turbine is fixed at the sought after value, in the ‘active’ mode, the discharge is regulated according to the required value. The design criterion is then presented, based on a simple relationship linking dimensionless numbers. A PRS is finally designed for a typical water distribution network, serving the city of Palermo (Italy). The resulting cost-benefit analysis is compared with a similar one carried out in previous work for a regulation system based on the use of a Pump As Turbine (PAT). The comparison shows the improvement obtained by the use of the PRS, consisting of higher energy production, as well as lower construction and installation costs.

In order to predict and control the impacts of floods in torrents, it is important to verify the simulation accuracy of the most used hydrological models. The performance verification is particularly needed for applications in watersheds with peculiar climatic and geomorphological characteristics, such as the Mediterranean torrents. Moreover, in addition to the accuracy, other factors affect the choice of software by stakeholders (users, modellers, researchers, etc.). This study introduces a “performance matrix”, consisting of several evaluation parameters weighted by stakeholders’ opinions. The aim is to evaluate the accuracy of the flood prediction which is achieved by different models, as well as the pros and cons of software user experience. To this aim, the performances and requisites of four physical-based and conceptual models (HEC-HMS, SWMM, MIKE11 NAM and WEC-FLOOD) have been evaluated, by predicting floods in a midsized Mediterranean watershed (Mèsima torrent, Calabria, Southern Italy). In the case study, HEC-HMS and MIKE 11 NAM were the best computer models (with a weighted score of 4.45 and 4.43, respectively), thanks to their low complexity and computation effort, as well as good user interface and prediction accuracy. However, MIKE11 NAM is not free of charge. SWMM showed a lower prediction accuracy, which put the model in third place of the four models. The performance of WEC-FLOOD, although not being as good as for the other tested models, can be considered overall acceptable in comparison to the other well-consolidated models, considering that WEC-FLOOD is in the early stage of development. Overall, the proposal of the performance matrix for hydrological models may represent a first step in building a more complete evaluation framework of the hydrological and hydraulic commercial models, in order to give indications to allow potential users to make an optimal choice.

The design of a novel Banki–Michell type turbine, to be located in existing water pipelines, is proposed. The turbine has a very efficient diffuser which allows the turbine to be compact and, most importantly, to have in-line flanges for minimal piping modifications at existing sites. This turbine combines a simple geometry with stable efficiency in a wide range of water discharges. The design procedure estimates the outer diameter of the impeller, its width and the geometry of the diffuser. A series of experimental tests has been carried out to measure the efficiency of the proposed turbine prototype. The turbine was tested in two different configurations, with and without rotational velocity regulation. The results of the tests showed that rotational velocity adaptation improves turbine efficiency in a wide range of flow rates. A significant reduction of the optimal velocity ratio, with respect to the predicted values, is likely due to 3D effects not accounted for in the design procedure. A simple way to roughly estimate this extra energy dissipation is derived from experimental data.

An important component of the management cost of aqueducts is given by the energy costs. Part of these costs can be recovered by transforming some of the many existing energy dissipations in electric energy by means of economic turbines. In this study an experimental work has been carried out: 1) to test the performance of an economic Cross-Flow turbine which maintains high efficiency within a large range of water discharges, and 2) to validate a new approximated formula relating main inlet velocity to inlet pressure. It is proved that the proposed formula, according to some simplifying assumption, exactly links inlet velocity to inlet pressure according to any possible geometry of the Cross-Flow turbine