# Full-Scale Experimental Investigation of the Interaction between Trains and Tunnels
## 1 Introduction
### The Importance of Full-Scale Experimental Tests  
As previously mentioned, issues regarding the pressure variations in tunnel are well defined in European standards. In detail, the test procedure for evaluating the pressure signature is described in the EN 14067-1, -3, and -5, while some limits and targets are depicted in different standard, i.e.,  
* The limits for the pressure signature \(\Delta\)Ps [1];
* A health criterion to prevent ear damage for weaker people (young babies, ill people, specific disease) [3];
* Basic criteria for pressure comfort on-board during tunnel crossings [7];
* Structural dimensioning for interoperability [2]. Practically, it is impossible to carry out an experimental campaign with two trains crossing in a tunnel, testing all the possible delays and measuring the pressure along the entire tunnel length and on the two trains. As a consequence, the above-mentioned criteria must be verified by numerical codes. On the other hand, the validation procedure of these numerical codes by using experimental data is a key aspect for the approval of a train and for the estimate of the maxima aerodynamic loads that a train has to withstand. Although the phenomenon of the overpressures in tunnel has been well known for decades, in Europe it started to become of primary importance in the 1990s, along with the construction of new HS lines throughout the continent. In order to study the major aerodynamic problems caused by the increase in speed over 200 km/h, 12 institutions (eight universities and four railways companies) from six countries came together to establish the first European project that started at the end of 1995 and ended in 1999: the TRANSAERO [35, 36]. The acronym TRANSAERO stand for \"TRANSient AErodynamics for Railways system Optimisation,\" in order to underline the interest of the project in the time-dependent phenomena being studied, namely, cross-wind, train pressure pulses, and waves in tunnels. With regards to the pressure pulses, since the remedies until then had consisted of increasing the cross-section of tunnels dramatically and of sealing trains (both of which are very expensive), the project gave a sharp acceleration in this area through experimental tests (both full-scale and small scale) and numerical codes. Since then, numerous numerical calculation methods have been proposed to try to reproduce the generation of the waves on the one hand and the evolution of the waves along the tunnel on the other. The typologies of numerical simulations can be divided into two mainly categories: on the one hand the CFD [37, 38, 39] and, on the other, the 1-D codes [40, 41, 42, 43]. CFD simulations can reproduce the entry of the train and the consequent pressure signature or the entire passage in the tunnel being studied. This allows to investigate the effect of geometry changes to both the tunnel and the trains (portals and heads shapes, vent holes, internal cavities, and many other solutions), although with very high computational costs. On the other hand, the 1-D simulations mainly deal with the evolution of the pressure waves within a tunnel. A mathematical model recreates the pressure waves at the entrance, while the evolution along the tunnel is managed by the codes through the physical laws of gas dynamics. In case of a 1-D code, the computational cost is reduced by orders of magnitude. Thus, while the CFD can be used to optimize the geometrical characteristics of the train and tunnels at the design stage, 1-D codes can be used to simulate the crossings between two trains investigating all possible delays in different tunnels. Of course, like any numerical code, both codes must be validated through experimental tests, especially the 1-D codes, since they require careful optimization of the parameters needed to recreate the pressure signature. The data shown in the present work have been used to set the parameters of the 1-D code called TRUNS, which is an open package made available after the end of the AeroTRAIN project.