Transversal Ventilation of Highway Tunnels: Long Duct Behavior.

It is a known fact that a long ventilation duct having a constant cross section and designed to operate with a uniform rate of outflowing air per unit length, behaves as follows: switching from nominal to a reduced air flow rate the outflowing air quantity shows a ″distortion″ insomuch as it decreases along the duct. The scope of this paper is to investigate the behavior of highway tunnel ducts at the conditions specified above for various values of length and wall roughness, in order to establish within what limits the ventilation may be acceptable. It is concluded that transversal ventilation in long tunnels by means of single delivery ducts seems to be possible and efficient within certain limits at least as far as the distortion occurring during the transition from the nominal to the reduced flowrate is concerned.