Wall 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.

In many countries, private tanks are acquired by users to reduce their vulnerability to intermittent supply. The presence of these local reservoirs modifies the user demand pattern and usually increases user water demand at the beginning of the service period depending on the tank filling process. This practice is thus responsible for the inequality that occurs among users: those located in advantaged positions of the network are able to obtain water resources soon after the service period begins, while disadvantaged users have to wait much longer, after the network is full. This dynamic process requires the development of ad hoc models in order to obtain reliable results. This paper discusses a numerical model used for evaluating this complex process as well as the application of model to an Italian case study. The model agreed with calibration data and provided interesting insights into the network filling process.

In many countries, users acquire private tanks to reduce their vulnerability to water scarcity. In such conditions, water managers often apply intermittent distribution in order to reduce the water volumes supplied to the users. This practice modifies the hydraulic behaviour of the network and determines competition among users that need to collect enough water resource for their uses.Intermittent distribution is thus responsible for the inequality that can occur among users: those located in advantaged positions of the network are able to obtain water resources soon after the service period begins, while others have to wait much longer, after the network is full. This paper analyses the inequalities that take part when intermittent distribution is applied in water scarcity scenarios. Considering the complexity of the process, the analysis was performed by means of an unsteady numerical model. The model was applied to a real case study which provided interesting insights into the network filling process, helping to highlight the advantaged and disadvantaged areas of the network in different water scarcity scenarios.

Turbulent flow in a channel with irregular two-dimensional rough surfaces is analysed\ud through wall-resolving large eddy simulation (LES). Both walls of the channel are\ud roughened through the superimposition of sinusoidal functions having random amplitude\ud and four different wavelengths. The downward shift of the velocity profile in the\ud log region due to the roughness, known as roughness function, is well captured in the\ud simulations. The spanwise and wall-normal turbulence intensities are found to increase\ud with the roughness height, while the streamwise component decreases. The analysis\ud of the Reynolds stress anisotropy tensor highlights a tendency towards isotropisation,\ud confirmed by the vorticity rms. The analysis of the statistics shows that the effects of\ud the roughness on the turbulent flow are greatly related to the increase of the height\ud of the maximum peaks of the corrugations. Although the inner layer is dramatically\ud affected by the wall irregularities, the outer layer appears not affected by the specific\ud wall shape and a collapse of the turbulence statistics in smooth- and rough-wall conditions\ud is observed. Much of the present results are consistent with the observations\ud made over regular roughness, nevertheless the turbulence structures and the turbulent\ud kinetic energy production analysis shows that the turbulence dynamics are directly\ud affected by the local shape of the irregularities. The spatial inhomogeneities of the\ud height of the roughness peaks and of the cavity region locally modifies the structures\ud introducing variable length-scales. Overall the irregular roughness destroys the coherent\ud pattern of the flow selectively, depending on the spatial distribution of the higher\ud roughness peaks

Abstract:Complex systems of water distribution networks (WDS) are used to supply water to users. WDSs are systems where a lot of distributed energy is available. Historically, this energy is artificially dissipated by pressure reduction valves (PRVs), thanks to which water utilities manage the pressure level in selected nodes of the network. The present study explores the use of economic hydraulic machines, pumps as turbines (PATs) to produce energy in a small network located in a town close to Palermo (Italy). The main idea is to avoid dissipation in favor of renewable energy production. The proposed study is applied to a WDN typical of the Mediterranean countries, where the users, to collect water during the period of water scarcity conditions, install private tanks. The presence of private tanks deeply modifies the network from its designed condition. In the proposed analysis, the economic benefit of PATs application in water distribution networks has been investigated, accounting for the presence of users' private tanks. The analysis, carried out by mean of a mathematical model able to dynamically simulate the water distribution network with PATs, shows the advantage of their installation in terms of renewable energy recovery, even though the energy production of PATs is strictly conditioned by their installation position.

Deposition and resuspension mechanisms in particle-laden turbulent flows are\ud dominated by the coherent structures arising in the wall region. These turbulent\ud structures, which control the turbulent regeneration cycles, are affected by the\ud roughness of the wall. The particle-laden turbulent flow in a channel bounded\ud by irregular two-dimensional rough surfaces is analysed. The behaviour of dilute\ud dispersions of heavy particles is analysed using direct numerical simulations (DNS)\ud to calculate the three-dimensional turbulent flow and Lagrangian tracking to describe\ud the turbophoretic effect associated with two-phase turbulent flows in a complex wallbounded\ud domain. Turbophoresis is investigated in a quantitative way as a function of\ud the particle inertia. The analysis of the particle statistics, in term of mean particle\ud concentration and probability density function (p.d.f.) of wall-normal particle velocity,\ud shows that the wall roughness produces a completely different scenario compared to\ud the classical smooth wall. The effect of the wall roughness on the particle mass flux is\ud shown for six particle populations having different inertia

No abstract

No abstract