Application of distortion theory to tunnel physical modeling

Abstract

With extensive developments in subway construction, tunnel lengths have also increased. Relative to this, existing experimental tunnel model which limited by large length–width ratios are only applicable to short tunnels with lengths that are less than 1000 m. In order to facilitate the development of research on extra-long tunnels, the use of distortion model with different linear length scales in the longitudinal direction is proposed in this research. A three-dimensional dynamic mesh model of a tunnel is established and validated by experiments to investigate the tunnel flow field. A multiple dynamic mesh coupling model is also created to study the piston wind effect of multiple trains simultaneously traversing the same tunnel. The distortion theory is introduced. Considering the structure of tunnel, the ratio of longitudinal direction is varied which is bigger than the ratios of transverse and vertical directions to shorten the length of tunnel model. The maximum permissible distortion ratio, which can reflect the application range of distortion, is elaborated. Distortion models applied to tunnels with one train and two trains are investigated. The results show that distortion models are capable of reflecting the flow field variation trend in full-size tunnels. The errors in distortion models, however, increase with the distortion ratio, which has a maximum permissible value of 4. The results are expected to provide reference for the design of tunnel physical models.