In the last forty years, railway transportation in Europe changed considerably, with the development of high speed lines and trains with speeds up to 300km/h and higher. The design of new high-speed railway lines requires longer and more numerous tunnels, where aerodynamic effects limit the maximum allowed train velocity. Aerodynamic effects are even more relevant considering that the trend is to increase train speed and reduce the cross sectional area of tunnels. The recent interest on mixed traffic operation ask for a proper consideration of aerodynamic effects also on conventional trains that are not designed to withstand large pressure variation in tunnels, as high speed trains. The problem has to be addressed by railway infrastructure managers to design new tunnels, by railway line operators to rule traffic conditions and by train manufacturers to design new vehicles. Therefore, the knowledge of the unsteady aerodynamic field around the train is essential to the optimum choice of tunnel configuration, and mainly of the cross-section diameter, the presence of hoods and position of pressure relief ducts and also the design of the car-body structure, the train head geometry and the restrictions in train operations. In fact, to meet modern standards demand, new high-speed tunnels are going to be twin tube, single track and fitted with slab track: the worst scenario for the issues related to aerodynamic effects. The research developed in this master thesis work focuses on the aerodynamic phenomena occurring when a high speed train enters a tunnel. Pressure transients within tunnels is a well known issue. When a train enters a tunnel, its head produces a compression wave which travels through the tunnel, and, under certain conditions, results in the emission of a so called micro-pressure wave at the opposite portal. Those micro-pressure wave emissions can cause strong acoustic noise, which may cause vibrations on buildings nearby and annoy residents. With increasing train speeds and the construction of modern single track tunnels, those emissions play a significant role in the acoustic verification process. Moreover, a large amount of the pressure wave is reflected back by the end portal producing a pressure wave traveling in the opposite direction towards the entry portal. This reflection occurs any time the traveling pressure wave encounter a change of tunnel section (portals, large shafts, niches, presence of the train,..) producing a complex pressure field due to the superimposition of a large number of pressure waves traveling in different directions. Large instantaneous pressure conditions can therefore arise in the tunnel, whose effect on train and tunnel equipment depends on their sealing level. In Europe, significant work has been carried out over the last twenty years, through the collaboration of several European institutions within joint research projects, to develop standard procedures and limits gathered in the European standards EN 14067 \cite{en2017} and in Technical Specification for Interoperability (TSI) for infrastructure \cite{tsi}. Nevertheless, at the moment, there are still gaps and open points in the standards and more work needs to be done, since in some cases there is not yet a unified procedure and each country is progressing in its own way according to national necessity. An example is the sonic boom issue, which is a rather new issue in Europe and no unified acceptance criteria are defined yet regarding the noise emission. In my master thesis work, numerical tools to simulate the transient pressure conditions inside a tunnel, when one or two crossing trains are running through it, are developed and validated. The aim is to study how modifications in train and tunnel geometry influence and control the phenomenon. This approach is applied to the reduction of the micro-pressure wave emission from tunnel portals, working on the optimisation of the portal geometry and openings and the train head shape, and on the alleviation of the worst overpressure condition in tunnels, due to pressure waves superimposition during train crossings in tunnel, working on the optimisation of shafts position. In this study, a new fully three-dimensional CFD approach is presented for simulating the emission of the micro-pressure wave from the tunnel portal. To predict the micro-pressure wave emitted from long tunnels with reasonable computational resources, the problem has been divided into three sub-simulations: 1) the entrance of the train nose into the tunnel is simulated in a stand alone simulation, which is stopped once the compression wave is fully developed, spread uniformly through the whole tunnel section and far enough from the vehicle. The complexity of this simulation is related to the handling of the moving region containing the train; 2) the propagation of the generated wave through the tunnel is predicted using a moving domain, focusing only on the compression wave reducing the domain to solve and therefore the computational effort; 3) after the pressure wave has travelled through the whole tunnel, the exit portal and the open air around it are considered, and the emission of the pressure pulse to the environment is simulated. Results have been validated with measurements performed during an experimental campaign at the Euerwang tunnel in Germany, a 7.7 km long tunnel fitted with slab track and critical for the sonic boom issue. Specific measurements were performed to evaluate the steepening effect on the traveling pressure wave, with different train speed for numerical validation purposes. This CFD approach has been applied to evaluate the micro-pressure wave emission from a new high-speed tunnel and it has been coupled with an optimisation algorithm to find appropriate countermeasures to lower the emissions below acceptable values. In fact, recently, several countermeasures have been applied to weaken the initial compression wave. As previously mentioned, part of pressure waves energy is emitted in the environment and may produce vibrations and a loud noise, but most of the energy is reflected back into the tunnel causing unsteady pressure fluctuations, which can produce aural discomfort for passengers and structural fatigue on the vehicle. This problem is studied in this thesis developing an accurate procedure to predict also pressure variations in tunnels. Since a fully three-dimensional method would require excessive computational resources, a one dimensional approach is preferred for this second issue. There are one dimensional codes available, either commercially or distributed within a European project, but they are limited to grant numerical stability and solution convergence. The implementation of a new code was necessary also due to restrictions in designing the tunnel geometry with available codes. The numerical code developed in this work allows to predict the performance of elements (such as niches, close and open shafts) placed in the tunnel with the purpose of improving passengers comfort and reducing fatigue on the train. The numerical code has been validated with full scale measurements conducted recently in the Italian high speed line by Politecnico di Milano. Then, the code has been used to study the best position of pressure relief shafts, which alleviates pressure fluctuations in the critical case of two trains crossing in the tunnel. A case when excessive pressure variation on vehicles are generated, limiting train operational conditions and causing problems in mixed traffic applications.
Negli ultimi quarant'anni, il trasporto ferroviario è cambiato considerevolmente in Europa, con lo sviluppo di linee ad alta velocità e treni con velocità massime fino a 300 km/h e oltre. La progettazione di nuove linee ad alta velocità richiede lunghi e numerosi tunnel, dove gli effetti aerodinamici limitano la massima velocità ammissibile. Gli effetti aerodinamici sono ancora più importanti considerando che il tend è quello di aumentare la velocità dei treni e ridurre la sezione delle gallerie. Il recente interesse per operazioni di traffico misto ha richiesto di considerare gli effetti aerodinamici anche su treni convenzionali che non sono progettati per sopportare grandi variazioni di pressione nei tunnel, al contrario dei treni ad alta velocità. Il problema riguarda i costruttori di infrastrutture quando progettano nuove gallerie, gli operatori delle linee ferroviarie per gestire il traffico e i costruttori di treni nel momento in cui progettano un nuovo veicolo. Dunque, la conoscenza dell'aerodinamica del treno è essenziale per scegliere le migliori caratteristiche della galleria, principalmente la sezione, la presenza di portali e la posizione di camini per alleviare la pressione, e anche per la progettazione della struttura delle carrozze, per la progettazione della testa del treno e per il controllo del traffico. Infatti, per venire in contro ai moderni standard richiesti, i nuovi tunnel per l'alta velocità saranno a doppia galleria, binario singolo e equipaggiati con binari posati su traverse in cemento: il caso peggiore per i problemi legati agli effetti aerodinamici. La ricerca sviluppata in questa tesi specialistica è incentrata sugli effetti aerodinamici che avvengono quando un treno entra in una galleria. I transitori di pressione all'interno del tunnel sono un problema ben noto. Quando un treno entra in una galleria, la sua testa produce un'onda di compressione che viaggia all'interno del tunnel, e, sotto certe condizioni, risulta nell'emissione di una cosiddetta micro-pressure wave dal portale opposto. Queste emissioni di micro-pressure waves possono causare violenti rumori acustici, che possono portare a vibrazioni negli edifici vicini e disturbare i residenti. Con l'aumento della velocità del treno e la costruzione di moderno gallerie a binario singolo, queste emissioni giocano un ruolo significativo nella validazione acustica dell'infrastruttura. Per di piò, gran parte dell'onda di pressione viene riflessa indietro dal portale di uscita, producendo un'onda di pressione che viaggia in senso opposto in direzione del portale di ingresso. Questa riflessione avviene ogni volta che un'onda incontra un cambiamento di sezione nel tunnel (portali, camini, nicchie, presenza del treno,..) producendo un campo di pressione complesso a causa della sovrapposizione di un gran numero di onde di pressione che viaggiano in direzioni diverse. Una condizione di grande variazione di pressione può quindi avvenire nel tunnel, i cui effetti sul treno dipendono dal livello di sigillatura. In Europa, un lavoro importante è stato portato avanti negli ultimi vent'anni, attraverso la collaborazione di diversi istituzioni europee all'interno di progetti di ricerca, per sviluppare procedure standard e limitazioni raccolte negli standard europei EN 14067 \cite{en2017} e nelle "Technical Specification for Interoperability (TSI) for infrastructure" \cite{tsi}. Tuttavia, al momento, ci sono ancora punti aperti negli standard e altro lavoro deve essere fatto, siccome in alcuni casi non c'è ancora una procedura unificata e ogni paese sta procedendo per conto suo a seconda delle proprie necessità. Un esempio è il problema del "sonic boom", un proclema relativamente nuovo per l'Europa e non sono ancora stati definiti criteri di tolleranza per quanto riguarda l'emissione sonora. Nel mio lavoro di tesi magistrale, sono stati sviluppati metodi numerici per simulare i transotori di presione all'interno del tunnel, quando è attraversato da uno o due treni. Lo scopo è quello di studiare come modifiche alla geometria del treno o del tunnel influenzano e controllano il fenomeno. Questo approccio è applicato alla riduzione dell'emissione di micro-pressure waves dai portali, lavorando sull'ottimizzazione della geometria e delle aperture del portale e sulla forma del naso del treno, e alla attenuazione del caso peggiore per le overpressure nel tunnel, a causa della sovrapposizione durante l'incrocio di due treni, lavorando sulla posizione ottima per un camino. In questo studio, un nuovo approccio CFD è presentato per simulare l'emissione delle micro-pressure waves dai portali. Per predire la micro-pressure wave emessa da tunnel lunghi con ragionevoli risorse computazionali, il problema è stato diviso in tre parti: 1) l'ingresso del naso del treno nel tunnel è simulato in una simulazione a parte, che viene fermata quando l'onda di compressione è completamente sviluppata, diffusa uniformemente in tutta la sezione e abbastanza lontana del veicolo. La complessità di questa simulazione è legata alla gestione della regione in movimento contenente il treno; 2) la propagazione dell'onda generata all'interno del tunnel è simulata usando un dominio mobile, concentrandosi solo sull'onda di compressione in modo da ridurre il dominio da risolvere e quindi il costo computazionale; 3) dopo che l'onda ha viaggiato attraverso tutta la galleria, il portale d'uscita e l'aria attorno sono considerati, e l'emissione dell'impulso di pressione nell'ambiente è simulato. I risultati sono stati validati con misurazioni prese durante una campagna al tunnel Euerwang in Germania, un tunnel lungo 7.7 km e equipaggiato con binari posati su traverse di cemento, critico per il problema del "sonic boom". Misure specifiche sono state condotte per valutare l'effetto di steepening sull'onda generata dal treno a diverse velocità, per motivi legati alla validazione del modello numerico. Questo approccio CFD è stato applicato per valutare l'emissione di micro-pressure waves da tunnel moderni, e può essere accopiato con un algoritmo di ottimizzazione per trovare contromisure appropriate per ridurre l'emmisione a livelli accettabili. Infatti, recentemente, diverse contromisure sono state applicate per ridurre la pendenza dell'onda iniziale. Come accennato in precedenza, parte dell'energia delle onde di pressione viene emessa nell'ambiente e può produrre vibrazioni e un forte rumore, ma la maggior parte dell'energia viene riflessa nel tunnel provocando fluttuazioni di pressioni, che possono provocare fastidi fisici per i passeggeri e fatica strutturale al veicolo. Questo problema è studiato in questa tesi, sviluppando una procedura accurata per prevedere anche le variazioni di pressione nelle gallerie. Poiché un metodo completamente tridimensionale richiederebbe risorse di calcolo eccessive, per questo secondo problema è preferibile un approccio monodimensionale. Sono disponibili codici unidimensionali, commerciali o distribuiti all'interno di un progetto europeo, ma sono limitati riguardo a stabilità numerica e convergenza delle soluzioni. L'implementazione di un nuovo codice era necessaria anche a causa delle restrizioni nella progettazione della geometria del tunnel con i codici disponibili. Il codice numerico sviluppato in questo lavoro consente di prevedere le prestazioni di elementi (come nicchie, camini chiusi o aperti) collocati nel tunnel con lo scopo di migliorare il comfort dei passeggeri e ridurre la fatica sul treno. Il codice numerico è stato validato con misurazioni in scala reale, condotte recentemente nella linea italiana ad alta velocità dal Politecnico di Milano. Quindi, il codice è stato utilizzato per studiare la migliore posizione dei camini verso l'esterno, che alleviano le fluttuazioni di pressione nel caso critico di due treni che si incrociano nel tunnel. Un caso in cui si generano variazioni eccessive di pressione sui veicoli, limitando le condizioni operative del treno e causando problemi nelle situazioni di traffico misto.
Aerodynamic interaction between high-speed trains and tunnels
MANDUCHI, GIONATA
2018/2019
Abstract
In the last forty years, railway transportation in Europe changed considerably, with the development of high speed lines and trains with speeds up to 300km/h and higher. The design of new high-speed railway lines requires longer and more numerous tunnels, where aerodynamic effects limit the maximum allowed train velocity. Aerodynamic effects are even more relevant considering that the trend is to increase train speed and reduce the cross sectional area of tunnels. The recent interest on mixed traffic operation ask for a proper consideration of aerodynamic effects also on conventional trains that are not designed to withstand large pressure variation in tunnels, as high speed trains. The problem has to be addressed by railway infrastructure managers to design new tunnels, by railway line operators to rule traffic conditions and by train manufacturers to design new vehicles. Therefore, the knowledge of the unsteady aerodynamic field around the train is essential to the optimum choice of tunnel configuration, and mainly of the cross-section diameter, the presence of hoods and position of pressure relief ducts and also the design of the car-body structure, the train head geometry and the restrictions in train operations. In fact, to meet modern standards demand, new high-speed tunnels are going to be twin tube, single track and fitted with slab track: the worst scenario for the issues related to aerodynamic effects. The research developed in this master thesis work focuses on the aerodynamic phenomena occurring when a high speed train enters a tunnel. Pressure transients within tunnels is a well known issue. When a train enters a tunnel, its head produces a compression wave which travels through the tunnel, and, under certain conditions, results in the emission of a so called micro-pressure wave at the opposite portal. Those micro-pressure wave emissions can cause strong acoustic noise, which may cause vibrations on buildings nearby and annoy residents. With increasing train speeds and the construction of modern single track tunnels, those emissions play a significant role in the acoustic verification process. Moreover, a large amount of the pressure wave is reflected back by the end portal producing a pressure wave traveling in the opposite direction towards the entry portal. This reflection occurs any time the traveling pressure wave encounter a change of tunnel section (portals, large shafts, niches, presence of the train,..) producing a complex pressure field due to the superimposition of a large number of pressure waves traveling in different directions. Large instantaneous pressure conditions can therefore arise in the tunnel, whose effect on train and tunnel equipment depends on their sealing level. In Europe, significant work has been carried out over the last twenty years, through the collaboration of several European institutions within joint research projects, to develop standard procedures and limits gathered in the European standards EN 14067 \cite{en2017} and in Technical Specification for Interoperability (TSI) for infrastructure \cite{tsi}. Nevertheless, at the moment, there are still gaps and open points in the standards and more work needs to be done, since in some cases there is not yet a unified procedure and each country is progressing in its own way according to national necessity. An example is the sonic boom issue, which is a rather new issue in Europe and no unified acceptance criteria are defined yet regarding the noise emission. In my master thesis work, numerical tools to simulate the transient pressure conditions inside a tunnel, when one or two crossing trains are running through it, are developed and validated. The aim is to study how modifications in train and tunnel geometry influence and control the phenomenon. This approach is applied to the reduction of the micro-pressure wave emission from tunnel portals, working on the optimisation of the portal geometry and openings and the train head shape, and on the alleviation of the worst overpressure condition in tunnels, due to pressure waves superimposition during train crossings in tunnel, working on the optimisation of shafts position. In this study, a new fully three-dimensional CFD approach is presented for simulating the emission of the micro-pressure wave from the tunnel portal. To predict the micro-pressure wave emitted from long tunnels with reasonable computational resources, the problem has been divided into three sub-simulations: 1) the entrance of the train nose into the tunnel is simulated in a stand alone simulation, which is stopped once the compression wave is fully developed, spread uniformly through the whole tunnel section and far enough from the vehicle. The complexity of this simulation is related to the handling of the moving region containing the train; 2) the propagation of the generated wave through the tunnel is predicted using a moving domain, focusing only on the compression wave reducing the domain to solve and therefore the computational effort; 3) after the pressure wave has travelled through the whole tunnel, the exit portal and the open air around it are considered, and the emission of the pressure pulse to the environment is simulated. Results have been validated with measurements performed during an experimental campaign at the Euerwang tunnel in Germany, a 7.7 km long tunnel fitted with slab track and critical for the sonic boom issue. Specific measurements were performed to evaluate the steepening effect on the traveling pressure wave, with different train speed for numerical validation purposes. This CFD approach has been applied to evaluate the micro-pressure wave emission from a new high-speed tunnel and it has been coupled with an optimisation algorithm to find appropriate countermeasures to lower the emissions below acceptable values. In fact, recently, several countermeasures have been applied to weaken the initial compression wave. As previously mentioned, part of pressure waves energy is emitted in the environment and may produce vibrations and a loud noise, but most of the energy is reflected back into the tunnel causing unsteady pressure fluctuations, which can produce aural discomfort for passengers and structural fatigue on the vehicle. This problem is studied in this thesis developing an accurate procedure to predict also pressure variations in tunnels. Since a fully three-dimensional method would require excessive computational resources, a one dimensional approach is preferred for this second issue. There are one dimensional codes available, either commercially or distributed within a European project, but they are limited to grant numerical stability and solution convergence. The implementation of a new code was necessary also due to restrictions in designing the tunnel geometry with available codes. The numerical code developed in this work allows to predict the performance of elements (such as niches, close and open shafts) placed in the tunnel with the purpose of improving passengers comfort and reducing fatigue on the train. The numerical code has been validated with full scale measurements conducted recently in the Italian high speed line by Politecnico di Milano. Then, the code has been used to study the best position of pressure relief shafts, which alleviates pressure fluctuations in the critical case of two trains crossing in the tunnel. A case when excessive pressure variation on vehicles are generated, limiting train operational conditions and causing problems in mixed traffic applications.File | Dimensione | Formato | |
---|---|---|---|
thesis.pdf
non accessibile
Descrizione: Master Thesis
Dimensione
23.99 MB
Formato
Adobe PDF
|
23.99 MB | Adobe PDF | Visualizza/Apri |
I documenti in POLITesi sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/10589/146276