This thesis deals with the classification of the different types of flow patterns that can develop in a rectangular shallow reservoir. After a bibliographic research, with the aim to get knowledge on the state of the art on the subject, the first part of the work has been an experimental activity carried out in the Laboratory of Hydraulic Construction at the Ecole Polytechnique fédérale de Lausanne. From this research, a wide overview has been obtained on the types of flow patterns that can develop in different reservoir configurations depending on reservoir geometry, at fixed hydraulic conditions. The interest in the investigation of flow patterns types is generated by the strong influence that the fluid-dynamic of the reservoir exerts on the sedimentation processes inside the reservoir. The idea is that, if we better know the fluid-dynamics of the reservoir, then we could also manage in a more effective and efficient way the sediments deposits in the reservoir. So, as far as concerns sediments, experiments were also carried out in order to observe at laboratory scale the influence that the velocity field exerts on sediments deposition of suspended solids entering in the reservoir. Then, a numerical activity has been carried out in collaboration with Liège University, with the aim to have a numerical model able to reproduce the velocity fields experimentally found. The experimental data previously collected have been the basis to validate the numerical model WOLF2D, which revealed to be able to reproduce in a quite accurate way and in numerous reservoir configuration, the experimental results. So, thanks to the validated numerical model, it has been possible to test new reservoir configurations, changing the boundary conditions of the problem. In particular not only the geometry of the reservoir could be easily modified, but also the hydraulic condition were varied, in order to extend the classification of the developing flow patterns not only as a function of reservoir geometry but also on the basis of the hydraulic conditions of the system, reaching a more complete view of the phenomenon. The change of the hydraulic conditions opens a wide range of possible combinations of the non-dimensional hydraulic parameters of the system (mainly the Reynolds and Froude numbers), which could lead to different types of flow patterns and to a future flow patterns classification not only based on the geometry of the reservoir but also as a function of the hydraulics of the reservoir. For the moment, the change of the inlet Froude number, that is to say the Froude number of the inlet channel, has shown the existence of a new type of flow pattern, not registered in the previous experiments object of this thesis: it is the meandering flow, whose characteristics have been partially investigated in this thesis by numerical simulations. The aim is, in future, to collect quantitative experimental data in order to confirm the numerical model results, even if the existence of this type of flow pattern has been already assessed also from the experimental point of view. The numerical model WOLF2D has been also endowed with a suspended sediments transport module, by which the deposition process of suspended load can be modelled; the aim is to reproduce the sediments deposits thickness and the global trapping efficiency of the reservoirs configurations experimentally tested, in order to develop a suspended sediment transport model available to simulate other reservoir configurations, changing sediments characteristics or hydraulics parameters, and evaluating their influence on the sedimentation processes.
Questa tesi riguarda la classificazione dei diversi tipi di campi di moto che possono svilupparsi in un serbatoio rettangolare di acque basse. Dopo una ricerca bibliografica, avente lo scopo di acquisire la conoscenza dello stato dell’arte su questo argomento, la prima parte del lavoro è stata una attività sperimentale condotta nel Laboratorio di Costruzioni Idrauliche presso l’Ecole Polytechnique fédérale di Losanna. Tramite questa ricerca, è stato possibile ottenere un ampio sguardo sui tipi di campo di moto che possono svilupparsi in differenti configurazioni geometriche del serbatoio a condizioni idrauliche fissate. L’interesse in questo studio è generato dalla forte influenza che la fluido dinamica del serbatoio esercita sui processi di sedimentazione all’interno del serbatoio stesso. L’idea è che, se conosciamo meglio la fluidodinamica del serbatoio, possiamo anche trattare in modo più efficiente i depositi di sedimenti nel serbatoio. A questo proposito, per quanto concerne i sedimenti, sono anche stati condotti esperimenti per osservare a scala di laboratorio l’influenza che il campo di moto esercita sulla deposizione di solidi sospesi entranti nel serbatoio. In seguito, un’attività numerica è stata condotta in collaborazione con l’università di Liegi, con lo scopo di ottenere un modello numerico capace di riprodurre i campi di moto trovati sperimentalmente. I dati sperimentali raccolti precedentemente sono stati la base con cui validare il modello numerico WOLF2D, che si è rivelato essere in grado di riprodurre in modo abbastanza accurato, e in numerose configurazioni geometriche, i risultati sperimentali. Così, grazie al modello numerico validato, è stato possibile testare nuove configurazioni del serbatoio, cambiando le condizioni al contorno del problema. In particolare, è stato possibile modificare non solo la geometria del serbatoio, ma anche le condizioni idrauliche, in modo da estendere la classificazione dei campi di moto non solo in funzione della geometria ma anche sulla base delle condizioni idrauliche del sistema, raggiungendo una visione più completa del fenomeno. Il cambiamento delle condizioni idrauliche apre un ampio spettro di possibili combinazioni dei parametri adimensionali del sistema (il numero di Reynolds e il numero di Froude), che possono portare a diversi tipi di campi di moto e a una futura classificazione dei campi di moto basata non solo sulla geometria del serbatoio ma anche in funzione delle condizioni idrauliche. Per il momento, la modifica del numero di Foude del canale di ingresso ha mostrato l’esistenza di un nuovo tipo di campo di moto, non registrato negli altri esperimenti oggetto di questa tesi: esso è il meandering flow , le cui caratteristiche sono state parzialmente investigate in questa tesi tramite simulazioni numeriche. Lo scopo è, in futuro, collezionare dati sperimentali quantitativi in modo da confermare i risultati del modello numerico, anche se l’esistenza di questo tipo di campo di moto è stata già appurata anche dal punto di vista sperimentale. Il modello numerico WOFL2D è stato anche dotato di un modulo di trasporto solido in sospensione, per mezzo del quale il processo di deposizione dei solidi sospesi può essere modellato; lo scopo è riprodurre lo spessore dei depositi di sedimenti e la trapping efficiency delle configurazioni di serbatoio testate sperimentalmente, in modo da sviluppare un modello di trasporto solido dei solidi sospesi che sia disponibile per simulare altre configurazioni di serbatoio, cambiando le caratteristiche dei sedimenti o i parametri idraulici, e valutare così la loro influenza sul processo di sedimentazione.
Investigation of flow patterns and sedimentation in rectangular shallow reservoirs
CAMNASIO, ERICA
Abstract
This thesis deals with the classification of the different types of flow patterns that can develop in a rectangular shallow reservoir. After a bibliographic research, with the aim to get knowledge on the state of the art on the subject, the first part of the work has been an experimental activity carried out in the Laboratory of Hydraulic Construction at the Ecole Polytechnique fédérale de Lausanne. From this research, a wide overview has been obtained on the types of flow patterns that can develop in different reservoir configurations depending on reservoir geometry, at fixed hydraulic conditions. The interest in the investigation of flow patterns types is generated by the strong influence that the fluid-dynamic of the reservoir exerts on the sedimentation processes inside the reservoir. The idea is that, if we better know the fluid-dynamics of the reservoir, then we could also manage in a more effective and efficient way the sediments deposits in the reservoir. So, as far as concerns sediments, experiments were also carried out in order to observe at laboratory scale the influence that the velocity field exerts on sediments deposition of suspended solids entering in the reservoir. Then, a numerical activity has been carried out in collaboration with Liège University, with the aim to have a numerical model able to reproduce the velocity fields experimentally found. The experimental data previously collected have been the basis to validate the numerical model WOLF2D, which revealed to be able to reproduce in a quite accurate way and in numerous reservoir configuration, the experimental results. So, thanks to the validated numerical model, it has been possible to test new reservoir configurations, changing the boundary conditions of the problem. In particular not only the geometry of the reservoir could be easily modified, but also the hydraulic condition were varied, in order to extend the classification of the developing flow patterns not only as a function of reservoir geometry but also on the basis of the hydraulic conditions of the system, reaching a more complete view of the phenomenon. The change of the hydraulic conditions opens a wide range of possible combinations of the non-dimensional hydraulic parameters of the system (mainly the Reynolds and Froude numbers), which could lead to different types of flow patterns and to a future flow patterns classification not only based on the geometry of the reservoir but also as a function of the hydraulics of the reservoir. For the moment, the change of the inlet Froude number, that is to say the Froude number of the inlet channel, has shown the existence of a new type of flow pattern, not registered in the previous experiments object of this thesis: it is the meandering flow, whose characteristics have been partially investigated in this thesis by numerical simulations. The aim is, in future, to collect quantitative experimental data in order to confirm the numerical model results, even if the existence of this type of flow pattern has been already assessed also from the experimental point of view. The numerical model WOLF2D has been also endowed with a suspended sediments transport module, by which the deposition process of suspended load can be modelled; the aim is to reproduce the sediments deposits thickness and the global trapping efficiency of the reservoirs configurations experimentally tested, in order to develop a suspended sediment transport model available to simulate other reservoir configurations, changing sediments characteristics or hydraulics parameters, and evaluating their influence on the sedimentation processes.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/57181