Antonio Petrillo

Experimental study of a vertical jet in a vegetated crossflow.

Aquatic ecosystems have long been used as receiving environments of wastewater discharges. Effluent discharge in a receiving water body via single jet or multiport diffuser, reflects a number of complex phenomena, affecting the ecosystem services. Discharge systems need to be designed to minimize environmental impacts. Therefore, a good knowledge of the interaction between effluents, discharge systems and receiving environments is required to promote best environmental management practice. This paper reports innovative 3D flow velocity measurements of a jet discharged into an obstructed crossflow, simulating natural vegetated channel flows for which correct environmental management still lacks in literature. In recent years, numerous experimental and numerical studies have been conducted on vegetated channels, on the one hand, and on turbulent jets discharged into unvegetated crossflows, on the other hand. Despite these studies, however, there is a lack of information regarding jets discharged into vegetated crossflow. The present study aims at obtaining a more thorough understanding of the interaction between a turbulent jet and an obstructed crossflow. In order to achieve such an objective, a series of laboratory experiments was carried out in the Department of Civil, Environmental, Building Engineering and Chemistry of the Technical University of Bari - Italy. The physical model consists of a vertical jet discharged into a crossflow, obstructed by an array of vertical, rigid, circular and threaded steel cylinders. Analysis of the measured flow velocities shows that the array of emergent rigid vegetation significantly affects the jet and the ambient flow structures. It reduces the mean channel velocity, allowing the jet to penetrate higher into the crossflow. It significantly increases the transversal flow motion, promoting a major lateral spreading of the jet within the crossflow. Due to the vegetation array effects, the jet undergoes notable variations in its vortical structure. The variation of the flow patterns affects the mixing process and consequently the dilution of pollutants discharged in receiving water bodies.

Discharge estimation in open channels by means of water level hydrograph analysis

A new methodology, based on the synchronous measurement of stage hydrographs in two river sections located some kilometres from each other, was developed to estimate the discharge hydrograph in the upstream section. The methodology is based on the one-parameter calibration of a numerical flow routing algorithm, solving the Saint-Venant equations in diffusive or complete form. The methodology was validated using results of laboratory experiments carried out at the Polytechnic of Bari University. A known discharge hydrograph was generated in the upstream tank of a rectangular flume, where two water level sensors were located. Two different bed materials have been used to account for different roughness coefficients. Eight measured discharge hydrographs have been compared with the hydrographs computed using both a diffusive and a fully dynamic model. The diffusive model provides a good estimate of the measured discharge in the experiments with the highest roughness value.

WAVE SPECTRA TRANSFORMATIONS

Tanah Lot Temple is situated in Tabanan Regency - Bali, on the coast of the Indonesian Ocean. Due to continuous wave attack, wind force, and weathering of the rock bank where the Temple stands, abrasion has occured which is more and more threatening the existence of the Temple. Considering that Tanah Lot Temple is a sacred place for the Hindu Balinese people and a place of high cultural value, and also an important tourism, steps to save the Temple are imperative. The Central as well as the Regional Authorities, and also the Bali nese community are very much interested in the effort to keep the Temple intact. Measures have been undertaken to protect both the seaside and land-side banks of the Temple rock bank. This paper only discusses counter measures of the sea —side bank of the Temple.

The influence of self-aeration on resistance in smooth and rough steep channels

SommarioVengono esaminate le resistenze al moto in un canale rettangolare largo con pendenza compresa fra 4° e 12° nellipotesi di considerare in moto uniforme la corrente areata che si stabilisce.Lanalisi dei dati rilevati sul canale sia con fondo liscio che scabro, ha evidenziato che, per la parte di corrente prevalentamente idrica, assumendo come significativa ai fini del calcolo dello sforzo alla parete laltezza h05, dove la concentrazione di aria è del 5%, lindice di resistenza può essere calcolato impiegando le leggi valide per le tubazioni senza bisogno di introdurre il fattore di forma.Si utilizza la relazione sperimentale che lega il numero di Froude della corrente allaltezza h05 per il proporzionamento idraulico del canale. Dello strato areato si forniscono le caratteristiche globali δh e δq mostrando come esse dipendono dalla turbolenza nello strato prevalentemente idrico e dalla portata.SummaryFlow resistance was examined in a wide rectangular channel with the bed sloping between 4° and 12°. The working hypothesis was that a uniform flow occurs in the resulting self-aerated stream at the gauging section.Analysis of data taken in the channel, both with a smooth and rough bottom, showed that in the portion of the stream formed essentially by water - and for which wall stress was calculated by assuming depth h05, where air concentration is 5%, as significant - the resistence index can be calculated with the laws applicable to pipes without any need to use the shape factor.The experimental relationship that relates Froudes number of the stream to depth h05 was used to calculate the hydraulic proportions of the channel. The overall characteristics δh and δq of the aerated layer are given. The paper shows that these characteristics depend on turbulence in the water layer and on discharge.

Fast flows in smooth channels

SommarioRichiamati brevemente i concetti della teoria della turbolenza in presenza di parete si riportano i risultati di esperienze eseguite su una canaletta liscia con pendenza variabile da 4° a 12°, con portate da q=0,076 a q=0,203 m2/s e con temperature di 15÷18° C.Per portate più piccole si è osservata la formazione di roll-waves superficiali più evidenti alle pendenze maggiori. Dallanalisi dei dati si è osservato che le correnti rapide sono caratterizzate da un livello di turbolenza più basso di quello rilevato in correnti a superficie libera in modo uniforme in alvei a piccola pendenza, anzi allaumentare dellinclinazione α, che determina un aumento della quantità di aria nella vena, la turbolenza diminuisce; questo comportamento, è uguale a quello riscontrato in correnti che trasportano materiale sottile in sospensione.Si riportano i diagrammi di velocità e si indica una possibile espressione della wake function che nella zona esterna si sovrappone alla distribuzione logaritmica della parete.SummaryAfter briefly going over the main concepts of the theory of turbulence in the presence of walls, this study reports the results of experiments carried out on a smooth channel with a slope of between 4° and 12°, discharges of between q=0.076 and q=0.203 m2/sec and with a temperature of between 15÷18° C.With small discharges, surface roll-waves were observed which became more apparent with steeper slopes. After studying the data, it was observed that fast flows give a lower turbulence level value than do uniform flows on free surfaces in low-slope beds. Indeed, as the inclination α increases, bringing an increased amount of air in the vein, the turbulence decreases. This behaviour is similar to that of streams carrying fine suspended material, which acts upon the flow by reducing turbulence.Velocity profiles are also given together with a possible expression for the wake function which, in the outer layer, is superposed on the logarithmic distribution of the wall.