Numerical studies on the critical velocity in bending tunnel

Critical velocity is the minimum air velocity required to suppress the smoke spreading against the longitudinal ventilation flow during tunnel fire situations. Former studies show that the critical velocity is concerned with the fire power, fire position and the tunnel geometry etc. Theoretical analysis and CFD simulation are performed in this paper to estimate the critical velocity for the bending tunnel with the different fire places. Results by CFD simulation show that when the fire originates near wall in bending tunnel, it needs larger critical velocity to arrest upwind movement of hot smoke. In research of bending tunnel, because of the route loss, the local loss of tunnel and with the effect of centripetal force, the critical velocity is concerned with radian. The critical velocity increases with the increasing of radian between 0 degrees and 90 degrees when the fire originates both at central and near the wall, while the critical velocity decreases with the increasing of radian between 90 degrees and 180 degrees.