Using a mean wind pressure coefficient is a common practice in tunnel ventilation studies. This parameter can be issued from generic databases or simple analytical method and, when combined with external wind data, it provides boundary conditions for internal flow computations. The latter computations are usually based on pressure drop calculations. This papers reports on wind tunnel experiments where the interaction of an atmospheric boundary layer with the jet of a tunnel is examined. The local distribution of the static pressure was measured with numerous surface taps at different sections of a small scale tunnel. Velocity ratios U_t/U_∞ in the range -1.5 to 3 were considered. U_t and U_∞ stand respectively for the tunnel jet velocity and the boundary layer free stream velocity. The experiments indicate that the pressure field at a tunnel portal can be very heterogeneous and could benefit from a better characterisation than that achieved through a mean pressure coefficient. It is established that the pressure at the portal is influenced by the ratio of the tunnel airflow velocity to wind speed, incident wind angle but also by the configuration of the space surrounding the tunnel. These experiments provide useful information for future improvement in wind-influenced tunnel ventilation studies.
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