1,721,066 research outputs found
Effects of irregular two-dimensional and three-dimensional surface roughness in turbulent channel flows
Full text linkOptimization of the design of labyrinth emitter for agriculture irrigation using computational fluid dynamic analysis
No full textFluid dynamic simulations are used to improve the efficiency of flat drippers commonly used in agriculture to optimize the irrigation system.. These emitters have a particular configuration of the labyrinth channel appropriately shaped to ensure high turbulence and dissipation of the hydraulic load. The analysis was carried out investigating the labyrinth geometry by means of computational fluid dynamics technique. Several simulations were performed in order to investigate on the relationship between the flow rate, in liters per hour, and the pipe pressure. Seven different dripper models were analyzed to change the size of the dissipation channel and therefore the flow rate. The emitter discharge was investigated for three inlet pressure values 50, 100 and 150 kPa. This way it was possible to calculate the law that rules the pressure-flow curve. Basically, the geometry was modified thus to optimize the exponent of the emitter. The value of the exponent is closely linked to the conformation of the channel and is standardized by the International Organization for Standardization (ISO) 9261:2004. Furthermore, the relation between the cross sectional area of the labyrinth channel and the flow rate was investigated
Editorial: Water and environmental challenges in a changing world: the perspective of the 13th International Conference on Hydroinformatics HIC 2018
Full text linkThe IAHR/IWA Joint Committee on Hydroinformatics is a community of scientists working on the application of information and communications technologies (ICTs) in addressing the increasingly serious problems of the equitable and efficient use of water in its various and really different forms. The community is thus composed of particularly wide and lively research areas widening from numerical modelling to the development of new sensors and tools, from the interpretation of increasing amounts of data, to the analysis and management of complex systems requiring the integration of physically based models, data and controls for practical applications. Today, multi-disciplinarity is the key to tackle challenges for sustainable management of water resources, especially considering the increasing complexity in the water world. It is thus fundamental to link the mathematical laws describing the water bodies and the new technologies given by the ICT and information science scientific communities.
In this framework, the 13th International Conference on Hydroinformatics 2018 (HIC 2018) held in Palermo, Italy, was the concrete location where researchers, working in very different areas related to water problems, over an entire week
The importance of “extensive teaching” in the education of prospective teachers of mathematics
Full text linkIn recent discussions on university curricula we fostered the idea that an extensive teaching of mathematics is needed in the education of prospective teachers. Most universities only provide courses on methodological didactical issues - if any - or intensive teaching, more suitable for prospective researchers. The goal of this paper is to clarify the meaning of extensive teaching, in the sense already considered in the work of Guido Castelnuovo, and to discuss its relevance today
Modelling of E. coli distribution in coastal areas subjected to combined sewer overflows
Full text linkRivers, lakes and the sea were the natural receivers of raw urban waste and storm waters for a long
time but the low sustainability of such practice, the increase of population and a renewed
environmental sensibility increased researcher interest in the analysis and mitigation of the impact of
urban waters on receiving water bodies (RWB). In Europe, the integrated modelling of drainage
systems and RWB has been promoted as a promising approach for implementing the Water
Framework Directive. A particular interest is given to the fate of pathogens and especially of
Escherichia coli, in all the cases in which an interaction between population and the RWB is foreseen.
The present paper aims to propose an integrated water quality model involving the analysis of
several sewer systems (SS) discharging their polluting overflows on the coast in a sensitive marine
environment. From a modelling point of view, the proposed application integrated one-dimensional
drainage system models with a complex three-dimensional model analysing the propagation in space
and time of E. coli in the coastal marine area. The integrated approach was tested in a real case study
(the Acicastello bay in Italy) where data were available both for SS model and for RWB propagation
model calibration. The analysis shows a good agreement between the model and monitored data.
The integrated model was demonstrated to be a valuable tool for investigating the pollutant
propagation and to highlight the most impacted areas
The effect of the slope of irregularly distributed roughness elements on turbulent wall-bounded flows
No full textWall roughness produces a downward shift of the mean streamwise velocity profile in the log region, known as the roughness function. The dependence of the roughness function on the height and arrangement of roughness elements has been confirmed in several studies where regular rough walls were analysed; less attention has been paid to non-regular rough walls. Here, a numerical analysis of turbulent flows over irregularly shaped rough walls is performed, clearly identifying the importance of a parameter, called the effective slope (ES) of the wall corrugations, in characterizing the geometry of non-smooth irregular walls. The effective slope proves to be one of the fundamental geometric parameters for scaling the roughness function. Specifically, for a moderate range of roughness heights, both in the transitionally and in the fully rough regime, ES appears to scale the roughness function for a wide range of irregular rough geometric configurations. The effective slope determines the relative importance of friction drag and pressure drag. For ES ~ 0.15 we find that the friction contribution to the total wall stress is nearly in balance with the pressure-drag contribution. This value separates the region where the roughness function ΔU+ = f(ES) is linear from that where a smooth nonlinear behaviour is observed. In the cases investigated, value ES ~ 0.15 also separates the transitionally rough regime from the fully rough regime
The role of the areal parameters on turbulent flow over 2D Gaussian roughness
No full textIn the past decades, numerous efforts have been dedicated to establishing a direct correlation between a geometric parameter that represents wall roughness and the corresponding velocity reduction, known as the Roughness Function ΔU+. This reduction is influenced by various statistical measures of roughness height, including average roughness height, peak-to-valley roughness distance, roughness root mean square, and Effective Slope, among others. It has been demonstrated that a singular measure of roughness height cannot sufficiently predict the Roughness Function across all turbulent regimes. Consequently, many studies have concentrated on identifying a universal correlation between roughness geometry and the downward shift of the mean velocity profile. In this study, we investigated the correlation between various geometrical parameters and the Roughness Function using Large Eddy Simulation (LES) techniques in channel flows at a friction Reynolds number of Reτ=400. Given the complexity introduced by the random nature of irregular roughness, we explored specific aspects of the relationship between wall irregularities and the roughness function by studying 2D geometries. This approach allowed us to systematically investigate the impact of geometrical properties on the roughness function and isolate the effects of roughness density and coverage area. Several irregular rough surfaces, characterized by different average oscillations height, different distributions and different densities, were designed throughout 2D Gaussian functions. With the aim to find a universal correlation between the roughness geometry and the Roughness Function, new geometrical quantities were investigated, based on the global area occupied by the roughness A∗. The prediction of the roughness function can be thus obtained using apriori data. To predict the roughness function, we introduced a parameter called Effective Area (EA), which is derived from the correlation between the Effective Slope (ES) and the roughness area A∗. Our findings indicate that a single geometric parameter, whether ES or Area A, is insufficient to predict the roughness effect. Conversely, combining these two parameters enhances predictive accuracy, at least for the proposed roughness model. This improvement can be attributed to the ability of ES to interpret the roughness distribution and height, while the coverage area is effective in predicting roughness density over a flat plate
Numerical simulation for water loss estimation in water supply pipes: Discharge estimation and deformation analysis
No full textIn recent decades, the changing scenario in the availability and the use of water has made the efficiency of water distribution systems (WDSs) management a topic of great importance, particularly in terms of leakage detection and control. The definition of the relationships, which relates the leak outflow and the relevant hydraulic parameters has received more and more increasing attention in literature. Here, the attention is mainly focused on the analysis of the behavior of different types of leak openings in pressurized pipes, taking into account the effect of rigid and deformable materials
Effect of roughness on elongated particles in turbulent channel flow
No full textIn this paper, we examine the deposition and resuspension of rigid elongated particles transported by turbulence in a channel bounded by two-dimensional roughness. To analyze these processes, we use an Euler–Lagrange approach based on Direct Numerical Simulation of the carrier phase and Lagrangian Particle Tracking of the dispersed phase. Four different channel configurations are considered: One is the classical channel flow bounded by smooth flat walls, whereas the other three correspond to a channel with walls of increasing roughness. The roughness shape is obtained by superimposition of sinusoidal functions with different amplitude k and is characterized by the mean absolute value of the amplitude, k̄= 0.012, 0.024 and 0.050 (k̄= 0 for a smooth wall). The friction Reynolds number is Reτ=150 for all cases. Particles are modeled as prolate ellipsoids and classified according to their aspect ratio λ. Three different particles sets are considered: λ=1, corresponding to the reference case of spheres, λ=3, corresponding to slightly elongated particles, and λ=10, corresponding to long fiber-like particles. The particle response time is St+=5 for all sets. In turbulent flow bounded by smooth walls, particles are known to accumulate preferentially in the near-wall region, leaving the central region of the channel scarcely populated. Wall roughness produces a completely different scenario: Particles exhibit a more homogeneous distribution along the wall-normal direction. We show that the aspect ratio does not affect the preferential distribution and the velocity statistics of the particles. The effect of elongation, however, becomes important for their preferential orientation, which is much weaker than in the smooth-walls case, in the near-wall region, while recovering the smooth-walls case in the outer region of the channel. This finding supports the validity of Townsend's similarity hypothesis, namely that the bulk flow dynamics are unaffected by the roughening of the bounding walls
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