Concept, design, construction and testing of an experimental facility for multi-point longitudinal air flow measurements in tunnels

Performing accurate measurements during a set of fire tests in a road tunnel is a notoriously difficult task to carry out. As in addition the full three-dimensional, unsteady problem is out of reach of numerical methods, the knowledge of the flow field inside road tunnels under fire conditions and also during normal operation is in many cases only approximate and partial. As a consequence, also the influence of road tunnel ventilation on fire development and spread are still not clarified, even for the simple longitudinal ventilation. Aiming at performing easy and accurate in situ measurements of the flow field in road tunnel under different conditions, a portable experimental facility including a survey rake with five bidirectional vane anemometers has been designed and built. This paper reports the design procedure of the measurement facility, all the details of the measurement chain and also results of the first experimental campaign carried out under the 11611 meters long Mont Blanc road tunnel. Unlike data provided by the S.C.A.D.A., a monotonic axial velocity profile resulted, which is theoretically justified in the case of semi-transverse ventilation.