A study on airflows induced by vehicle movement in road tunnels by the analysis of bulk data from tunnel sensors

A novel analytical formula is introduced for calculation the average longitudinal airflow velocity in tunnels as a result of the piston effect. Existing correlations were analyzed and reworked to better represent the piston effect of vehicles travelling in bulk, which allows relating the airflow velocity to not only average vehicle velocity, but also the traffic intensity and the traffic structure. The approach was validated using the recorded bulk data for an urban road tunnel located in Gdańsk (Poland). Air velocity, weather conditions, wind parameters at tunnel portals, traffic intensity and structure as well as average traffic speed by lane were recorded at 1 s intervals, and analyzed in form of 10 s and 5 min averages. Since ambient conditions may affect the flows inside the tunnel, their impact on flow measurements was studied with a numerical model of the tunnel portals. Despite its simplicity, the proposed model accurately predicted the air velocity due to vehicle movement. The significance of this approach is related to the ease of achieving the initial data, which allows for easy implementation in tunnel ventilation design, risk assessment methods, determination of initial conditions for fire related CFD analyses, continuous tunnel management or estimation of the potential of energy recuperation from airflow within the tunnel. The mean absolute error (MAE) of calculated air velocity to measurements was 0.28–0.38 m/s, with mean average percentage error (MAPE) of 7.8–10.9 %. The determination coefficient for the relation with the measured data was significantly over 0.9.