Experimental study on smoke movement characteristics in tunnel fires with different canyon cross wind yaw angles

High-speed canyon cross wind with random directions is common in mountain areas and induces complex threedimensional flow fields inside the tunnel while flowing across the tunnel portal, which changes smoke temperature distribution and movement characteristics in tunnel fires. The effect of canyon cross wind yaw angle on maximum ceiling gas temperature, position of maximum ceiling gas temperature, smoke back-layering length and downstream smoke spread length of tunnel fires was investigated by experiments. Results showed that the maximum ceiling gas temperature increased with the increasing wind yaw angle in the range of 45 degrees-90 degrees, but remained steady when the angle was in 90 degrees-135 degrees. The maximum ceiling gas temperature was higher than other fire locations when the fire was close to the upstream portal because of the airflow barrier. Additionally, a normalized maximum ceiling gas temperature linear correlation was established based on dimensional analysis. The position of maximum ceiling gas temperature was different in both horizontal and longitudinal directions due to the canyon wind. The transverse smoke distribution in the tunnel was uneven, which resulted in a double peak value phenomenon of ceiling gas temperature. Besides, when the wind yaw angle was in 45 degrees-90 degrees, the smoke back-layering was resisted and the downstream smoke spread was promoted by the canyon wind. However, the smoke back-layering was promoted and the downstream smoke spread was resisted due to the negative pressure induction when the angle was in 90 degrees-135 degrees.