Research On Smoke Movement Characteristics Of Subway Train Fire In Curved Tunnel

Compared with the straight tunnel,when the train have a fire in the curve tunnel,the longitudinal and transverse stress of the smoke changes,which leads to the difference of the smoke movement speed,affects the smoke transportation law in the tunnel,and the counterflow time of the smoke changes,which makes the temperature and concentration distribution of the smoke upstream and downstream of the fire source more complex.In this study,the three-dimensional unsteady Navier-Stokes equation and the Renormalization-group(RNG)k-eturbulence model are employed,the sliding grid technology is used to simulate the relative motion of the subway train and the tunnel,and the numerical simulation method of the curved tunnel subway fire is constructed.The accuracy of the numerical calculation method has been verified by tunnel fire moving model test.By simulating the fire scenarios of stationary train and moving train,the effects of tunnel curvature,fire source power and fire location on smoke movement law are studied,and the distribution characteristics of smoke flow velocity,temperature and carbon dioxide concentration under different fire scenarios are obtained.The main conclusions are as follows:When a stationary train catches fire in the tunnel,the curve radius of the tunnel will have an influence on the law of smoke movement.In a curved tunnel,the component of the static pressure caused by the temperature difference along the radial direction of the tunnel will make the smoke move centrifugally,so that the smoke temperature and carbon dioxide concentration are asymmetrically distributed along the transverse direction of the tunnel.The smaller the tunnel curve radius,the more obvious the blocking effect of tunnel wall and train body on smoke movement,and the greater the difference of smoke temperature and concentration between inside and outside the tunnel.Compared with the straight tunnel,the transition distance of stable stratification of smoke in the upstream of the fire source of the curved tunnel is shorter.With the increase of tunnel curve radius,the dimensionless neutral surface height H*and stratification state coefficient S_T show a downward trend outside150m from the fire source,and the stratification stability between hot smoke and cold air decreases.When the train moves with fire source in the tunnel,the piston wind plays a leading role in the longitudinal movement of smoke.At the time of train deceleration and parking,with the increase of tunnel curve radius,the peak value of smoke velocity decreases gradually,and the peak values of temperature and carbon dioxide concentration increase.After the train stops,with the increase of the curve radius of the tunnel,the blocking effect of the tunnel wall on the longitudinal movement of the air flow decreases,but the deceleration rate of the piston wind speed gradually increases,resulting in the time of smoke counterflow is delayed first and then advanced with the increase of curve tunnel radius.Compared with the tunnel with curve radius of 700m,the time of smoke counterflow in straight tunnel is 21s earlier.In curved tunnel with radius of 300m,compared with the head car fire,the smoke counterlow time of the middle car fire and the tail car fire is 17s and 30s earlier respectively.After the smoke counterflow,in case of fire in the tail car and middle car,the high concentration carbon dioxide is mainly concentrated in the tunnel ceiling,while the high concentration carbon dioxide smoke in the head car fire is mainly distributed in the window of the head car and the bottom of the tunnel.Compared with the head car fire,the middle car and tail car fire pose more serious threat to personnel escape.