Enrico Napoli

The effect of the slope of irregularly distributed roughness elements on turbulent wall-bounded flows

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.

Turbulence structures over irregular rough surfaces

Turbulent flow in a channel with irregular two-dimensional rough surfaces is analysed through wall-resolving large eddy simulation (LES). Both walls of the channel are roughened through the superimposition of sinusoidal functions having random amplitude and four different wavelengths. The downward shift of the velocity profile in the log region due to the roughness, known as roughness function, is well captured in the simulations. The spanwise and wall-normal turbulence intensities are found to increase with the roughness height, while the streamwise component decreases. The analysis of the Reynolds stress anisotropy tensor highlights a tendency towards isotropisation, confirmed by the vorticity rms. The analysis of the statistics shows that the effects of the roughness on the turbulent flow are greatly related to the increase of the height of the maximum peaks of the corrugations. Although the inner layer is dramatically affected by the wall irregularities, the outer layer appears not affected by the spe...

A model of the filling process of an intermittent distribution network

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.

Three-dimensional numerical simulations on wind- and tide-induced currents

The hydrodynamic circulation in the coastal area of the Augusta Bay (Italy), located in the eastern part of Sicily, is analysed. Due to the heavy contamination generated by the several chemical and petrochemical industries active in the zone, the harbour was declared a Contaminated Site of National Interest. To mitigate the risks connected with the industrial activities located near the harbour, it is important to analyse the hydrodynamic circulation in the coastal area. To perform such analysis, a parallel 3D numerical model is used to solve the Reynolds-averaged momentum and mass balance, employing the k-e turbulence model for the Reynolds stresses. The numerical model is parallelized using the programing technology - Message Passing Interface (MPI) and applying the domain decomposition procedure.The Augusta Bay circulation is mainly due to the relative contribution of the wind force acting over the free surface and the tidal motion through the mouths. Due to the geometric complexity of the domain and the presence of several piers along the coast, a curvilinear boundary-fitted computational grid was used, where cells corresponding to land areas or to wharfs were excluded from the computation. Comparisons between numerical results and field measurements were performed. Three different simulations were performed to selectively isolate the effect of each force, wind and tide, acting in the considered domain. The current in the basin was successfully estimated on the basis of the numerical results, demonstrating the specific role of wind and tidal oscillation in the hydrodynamic circulation inside the harbour. We model the hydrodynamic flow field induced by wind and tide.We examine the water volume exchange between open sea and lagoon.The importance of three dimensional numerical model is investigated.We validate the numerical model in complex environmental domain.We applied an Open source MPI parallel numerical models.

Modelling of E. coli distribution in coastal areas subjected to combined sewer overflows

Rivers, 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.

Three-dimensional numerical simulation of wind-driven flows in closed channels and basins

F. Cioffi, F. Gallerano And E. Napoli, Journal of Hydraulic Research 2005, 43(3), 290–301In the paper, a fully 3D finite-volume numerical model is developed and employed for the prediction of wind-induced flows in a regular channel and in a square basin with a complex bathymetry. Numerical results are compared with laboratory experiments.Numerical tests are then performed to investigate whether simplifying assumptions about the pressure distribution and the turbulente stresses representation can be employed in the simulation of wind-driven flows. The hydrostatic pressure assumption, resulting in the use of “quasi-3D” models, proved to be reasonably acceptable in order to obtain the vertical profile of the streamwise velocity component away from the boundaries. The quasi-3D model employed, nevertheless, provided incorrect velocity patterns near the upwind and downwind boundaries. The zero-equation turbulence model proposed by Tsanis [J. Hydraul. Div. ASCE 115 (1990) 1113] is also investigated by comparing the parabolic vertical profiles of the eddy viscosity coefficient assumed in this model w...

Wind- and tide-induced currents in the Stagnone lagoon (Sicily)

The hydrodynamic circulation is analyzed in the coastal lagoon of Stagnone di Marsala, a natural reserve located in the north-western part of Sicily, using both experimental measurements and numerical simulations. Field measurements of velocities and water levels, carried out using an ultrasound sensor (3D), are used to validate the numerical model. A 3D finite-volume model is used to solve the Reynolds-averaged momentum and mass balance differential equations on a curvilinear structured grid, employing the k–

Embedding Monitoring Systems for Cured-In-Place Pipes.

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