Window ejected thermal plume dispersion and recirculation behavior in urban street canyon with different building height ratios under wind

Fire scenario of street canyon, in which buildings had different heights, was investigated by Large Eddy Simulation (LES). To figure out the impact of street canyon layout on the smoke transportation behavior, side buildings in street canyon with different heights were built in this study. Simulation results showed that two regimes existed in the flow pattern of buoyancy plume. The critical re-entrainment phenomenon was defined as a critical criterion between the regimes. When the horizontal wind velocity exceeded the critical value, fire smoke would re-flow into the street canyon. An improved Froude number (Fr) considering the height difference of street canyon side buildings was proposed to quantify the dispersion pattern of fire smoke plume. The investigation showed that the Froude number was consistent when the critical re-entrainment wind velocities reached in different street canyons.