The effect of trains aerodynamics, considering in particular the air generated by the train slipstream during their passage, is of fundamental importance both to regulate the travel speeds of each train, and to verify the safety of passengers on the platform and of workers on the railway line. Due to the possible danger induced by the wind flows generated in the slipstream, in recent years many research activities have been undertaken to understand the development of this phenomenon in the open field, both for the homologation of new trains and for the verification of the maximum air velocity reached during their passage, following the guidelines given by the EN 14067-4 standard [6] and by the TSI [9]. In addition, previously performed analysis in which train passages have been studied in confined spaces, conducted by different authors mainly with scaled models (moving model rigs, wind tunnel testing) or with CFD analysis, have shown that the confinement of the air causes more severe conditions regarding to the speed of the air flow. Starting from the knowledge gained by the previous results, this thesis work aims to study in detail the effects of the flow confinement and of the various parameters of influence, linked to both the train and the infrastructure, on the air speed trend caused by the train passage. Through an experimental campaign with full-scale measurements at the Turin Rebaudengo site, considering both directions of travel and two different measurement positions from the center of the rails, it was possible to determine the slipstream conditions generated for each type and length of the trains during the acquisition period. From the data analysis it was possible to appreciate that the confinement given by the walls of the tunnel generates an acceleration of the air flow measured even before the train arrival in front of the measurement position, mainly due to the piston effect which does not develop in the open field. The results prove that, in tunnels, longer trains cause worse conditions with respect to shorter ones, for the same train type, and trains with a less optimized aerodynamic shape (freights or conventional passenger) cause faster gusts, for the same train length. Considering the influence of the train speed during each passage in the tunnel, it has been shown how faster trains generate higher flow rates, mainly in the boundary layer region, where a reverse flow develops, and at the tail of the train in the near wake region. In addition, a strong dependence of the slipstream air speeds on the local geometry of the infrastructure was noted, starting from the analysis of the passages on the two opposite sides of the examined tunnel, which is not symmetrical. The effects of the section variation in the tunnel on the air flow trend were also highlighted by a specific test carried out considering the presence of a stationary train on the track, to simulate a real condition of railway traffic. Finally, the presence of measurement stations both inside and outside the tunnel allowed to directly compare the passage of trains in the two different areas: during the passage of trains in front of the anemometers, especially for high-speed and conventional passenger trains passing the most critical tunnel side, the confinement of the flow develops higher air speeds compared to the passage in open field, specifically in the near wake area. Freight trains, on the other hand, have similar maximum air speeds for open field and tunnel passages, generally showing higher values than other train types.
L’effetto dell’aerodinamica dei treni, considerando in particolare l’aria generata dalla scia durante il loro passaggio, è di fondamentale importanza sia per regolare le velocità di percorrenza di ogni treno, sia per verificare la sicurezza dei passeggeri in banchina e dei lavoratori sulla linea ferroviaria. A causa del possibile pericolo indotto dai flussi di vento generati nella scia, negli ultimi anni sono state intraprese diverse attività di ricerca per comprendere lo sviluppo di questo fenomeno in campo aperto, sia per l’omologazione di nuovi treni, sia per la verifica delle massime velocità dell’aria raggiunte durante il passaggio degli stessi, seguendo le linee guida date dalla normativa EN 14067-4[6] e dalls TSI [9]. Ulteriori analisi svolte in precedenza in cui il passaggio dei treni è stato studiato in spazi confinati, condotti principalmente con modelli in scala o con analisi CFD, hanno dimostrato che il confinamento dell’aria provoca condizioni più gravose riguardo alla velocità del flusso. Partendo dalla conoscenza del fenomeno ottenuta con l’analisi dei risultati precedenti, questo lavoro di tesi si pone l’obiettivo di studiare nel dettaglio gli effetti del confinamento del flusso e dei vari parametri di influenza, legati sia al treno che all’infrastruttura, sull’andamento di velocità dall’aria spostata al passaggio del treno stesso. Attraverso una campagna sperimentale con misurazioni full-scale nel sito di Torino Rebaudengo, considerando entrambe le direzioni di marcia e due diverse posizioni di misura rispetto al centro delle rotaie, è stato possibile determinare le condizioni di scia generata per ogni tipologia e lunghezza dei treni acquisiti. Dalle analisi dei dati si è potuto apprezzare che il confinamento dato dalle pareti della galleria genera un’accelerazione del flusso d’aria misurata ancora prima dell’arrivo del treno, dovuta prevalentemente all’effetto pistone, che in campo aperto non si sviluppa. I risultati dimostrano come, in galleria, i treni più lunghi causano condizioni peggiori rispetto a quelli più corti, per la stessa tipologia di treno, e i treni che presentano una forma aerodinamica meno ottimizzata (treni merci e passeggeri convenzionali) causano flussi più veloci, a parità di lunghezza. Considerando invece l’influenza della velocità di passaggio dei treni in galleria, si è appreso come treni più veloci generino delle velocità di flusso più elevate, soprattutto nella regione dello strato limite, in cui si sviluppa un flusso contrario, e in coda al treno nella scia vicina. E’ stata notata, inoltre, una forte dipendenza delle velocità nella scia dalla geometria dell’infrastruttura, partendo dalle analisi dei passaggi nei due lati opposti della galleria in esame, la quale non è simmetrica. Gli effetti della variazione di sezione in galleria sull’andamento del flusso d’aria sono stati confermati anche da una prova specifica svolta considerando la presenza di un treno fermo su un binario, per simulare una condizione reale di traffico ferroviario. Infine, la presenza di stazioni di misura sia all’interno che all’esterno della galleria ha reso possibile un confronto diretto tra i passaggi dei treni nelle due differenti aree: durante il passaggio dei treni nelle zone di misura e soprattutto per treni ad alta velocità e regionali in passaggio sul binario più critico, il maggior confinamento del flusso sviluppa velocità più elevate rispetto al passaggio in campo aperto, prevalentemente nella zona della scia vicina. I treni merci, invece, sembrano presentare delle velocità massime dell’aria simili per i passaggi in campo aperto e in galleria, con valori più elevati rispetto alle altre tipologie di treno.
Experimental analysis of train slipstream in confined spaces
Negri, Stefano
2020/2021
Abstract
The effect of trains aerodynamics, considering in particular the air generated by the train slipstream during their passage, is of fundamental importance both to regulate the travel speeds of each train, and to verify the safety of passengers on the platform and of workers on the railway line. Due to the possible danger induced by the wind flows generated in the slipstream, in recent years many research activities have been undertaken to understand the development of this phenomenon in the open field, both for the homologation of new trains and for the verification of the maximum air velocity reached during their passage, following the guidelines given by the EN 14067-4 standard [6] and by the TSI [9]. In addition, previously performed analysis in which train passages have been studied in confined spaces, conducted by different authors mainly with scaled models (moving model rigs, wind tunnel testing) or with CFD analysis, have shown that the confinement of the air causes more severe conditions regarding to the speed of the air flow. Starting from the knowledge gained by the previous results, this thesis work aims to study in detail the effects of the flow confinement and of the various parameters of influence, linked to both the train and the infrastructure, on the air speed trend caused by the train passage. Through an experimental campaign with full-scale measurements at the Turin Rebaudengo site, considering both directions of travel and two different measurement positions from the center of the rails, it was possible to determine the slipstream conditions generated for each type and length of the trains during the acquisition period. From the data analysis it was possible to appreciate that the confinement given by the walls of the tunnel generates an acceleration of the air flow measured even before the train arrival in front of the measurement position, mainly due to the piston effect which does not develop in the open field. The results prove that, in tunnels, longer trains cause worse conditions with respect to shorter ones, for the same train type, and trains with a less optimized aerodynamic shape (freights or conventional passenger) cause faster gusts, for the same train length. Considering the influence of the train speed during each passage in the tunnel, it has been shown how faster trains generate higher flow rates, mainly in the boundary layer region, where a reverse flow develops, and at the tail of the train in the near wake region. In addition, a strong dependence of the slipstream air speeds on the local geometry of the infrastructure was noted, starting from the analysis of the passages on the two opposite sides of the examined tunnel, which is not symmetrical. The effects of the section variation in the tunnel on the air flow trend were also highlighted by a specific test carried out considering the presence of a stationary train on the track, to simulate a real condition of railway traffic. Finally, the presence of measurement stations both inside and outside the tunnel allowed to directly compare the passage of trains in the two different areas: during the passage of trains in front of the anemometers, especially for high-speed and conventional passenger trains passing the most critical tunnel side, the confinement of the flow develops higher air speeds compared to the passage in open field, specifically in the near wake area. Freight trains, on the other hand, have similar maximum air speeds for open field and tunnel passages, generally showing higher values than other train types.File | Dimensione | Formato | |
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Thesis.pdf
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Descrizione: Master of Science thesis - Stefano Negri
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Executive summary.pdf
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Descrizione: Executive Summary - Stefano Negri
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https://hdl.handle.net/10589/188730