# Full-Scale Experimental Investigation of the Interaction between Trains and Tunnels
## 1 Introduction
### The Importance of Full-Scale Experimental Tests
The code behind this software (TETUN, \"Train En TUNnel\") was also used and validated during the TRANSAERO project with the name of TRANSTUN [42; 44]. Many other codes exist, mainly developed by train manufacturers or infrastructure managers for practical purposes, although few literature and documentation are available, especially as regards the validation with full-scale data. Contrariwise, academic contributions are available, but full-scale data for comparison are very rare and validations using scale models is more common [28; 45; 46; 47; 48; 49; 50; 51; 52; 53]. Under laboratory conditions, it is possible to study the effects of the geometric characteristics on the pressure signature and the pressure gradient pressure. Furthermore, the waves superposition and reflection, which lasts for a longer time than the train passage, can also be investigated. In some cases, and generally with a high scale ratio (1:70-1:200), models with simplified shapes are used since they help the development of numerical codes by reducing the complexity of the phenomenon [54]. In other cases, the object is catapulted in a high-molecular-weight gas to carry out test under the real Mach number conditions, even with lower speeds [55; 56]. Besides these examples, however, there are test rigs with scale models of real trains to conduct both basic research and predictive/parametric industrial studies on most train passing issues. Thanks to its versatility, in recent years, many institutions have built similar devices all over the world [46; 57; 58; 59] by gradually increasing the speed and reducing the scale. On the other hand, these models suffer from the same problems faced for scale models used in wind tunnels: it is almost impossible to reproduce the right surface roughness of both track and train and to recreate all the details that characterize the underbody and roof regions. Moreover, the models are almost always composed of only three cars (leading, intermediate, and tailing). All these differences make it difficult to reproduce the second part of the pressure signature (\(\Delta\text{P}_{\text{FR}}\)). Finally, the degree of sealing of the train and the resulting \(\tau_{\text{dyn}}\) cannot be reproduced with scale models. For these reasons, although the numeric codes and the scale models are allowed by the EN standard, it still specifies that \"Full-scale test data may be the basis for train and tunnel acceptance and homologation.\" Therefore, full-scale experimental tests are the basis of the whole process [60]. However, despite their importance, not many examples of solid validations (using, for example, different tunnels, speeds, or cross-sections) of numerical models with full-scale experimental data are available in the literature, e.g., [61; 62; 23; 63]. In addition, in the presentation of the TRUNS software of the AeroTRAIN the results are still compared with experimental data of the TRANSAERO. Many data might be available within train manufacturers and railway operators, however, for confidentiality reasons, they have not been published. On the other hand, organizational difficulties combined with high costs of full-scale tests are probably the reasons why the data collected in the TRANSAERO have been considered as the reference for full-scale tests for the past 20 years, at least in Europe, and are adopted as a benchmark [19; 64]. This work deals with the above-presented subject: an experimental full-scale campaign has been carried out on the Italian HS railways lines, collecting a wide database for the validation of 1-D codes. These data, recorded both at trackside and on-board, allow to observe the pressure evolution within tunnels, focusing on the effect of different parameters.