Study On The Effect Of Additional Baffles On The Phenomenon Of Plug-holing In Tunnel Side Smoke Exhaust

When the rate of smoke exhaust from the side of the tunnel is too high,the cold air in the lower layer of the tunnel will be sucked in vertically and horizontally at the side smoke exhaust port,leading to a phenomenon of plug-holing and a decrease in the smoke exhaust efficiency of the system.By attaching three baffle plates to the smoke vent to form a three-sided enclosure,the direction of suction force is changed so that the smoke enters the vent directly from the vertical side.This can be attributed to the plate movement which simultaneously separated the hot smoke layer from the cold air layer,thus suppressing the plug-holing phenomenon and improving the smoke extraction efficiency of the system.To facilitate the practical implementation of the project,a submerged road tunnel is utilized as the subject of investigation in this study.Through numerical simulation,the optimal setting parameters for the additional baffles are determined,and the degree of improvement in the plug-holing phenomenon is quantitatively analyzed.Furthermore,the plug-holing phenomenon prediction formula for the side smoke exhaust mode of the additional baffle is studied.Firstly,the effect of six different opening angles of the smoke vent baffle on the smoke plug-holing phenomenon in the side smoke exhaust mode compared to that without the baffle was investigated,and the changes in the temperature field,flow field,and smoke extraction efficiency in the smoke vent area were studied through numerical simulations.The results show that a damper with an opening angle of 60°is the most effective way to suppress the phenomenon of smoke penetration,and the smoke exhaust efficiency of the system at this time is improved by about 4.3%compared to traditional centralized smoke exhaust.Secondly,on the basis of adding a baffle with an opening angle of 60°at the smoke outlet,by changing the size ratio of the baffle to the smoke outlet(k=L_DB/L_vent),a study was conducted under two fire scenarios.The results show that when the baffle size ratio k is 1,that is,when the baffle size and the smoke outlet size are the same,the pressure loss in the smoke outlet area is the smallest,the smoke exhaust capacity is the strongest,and the effect of suppressing plug-holing is the best.Finally,the Froude number of the smoke outlet with additional baffles under three types of fire source power was studied by changing the exhaust gas velocity.The results show that under the same smoke exhaust wind speed,adding a baffle of the same size with an opening angle of 60°in the smoke outlet can prevent smoke sedimentation,and hot smoke is better discharged,which is more conducive to personnel evacuation safety compared to the situation without a baffle.The smoke layer is disturbed in the middle of the side smoke vent,and the height of the smoke layer is determined by the longitudinal position 1m from the outside of the vent（near the fire source side）and the lateral position 0.3m from the vent.When the temperature at the bottom edge of the smoke outlet approaches the ambient temperature and the height of the smoke layer no longer changes,it is determined that the smoke exhaust wind speed at which complete penetration occurs is consistent.Through dimensionless analysis,a plug-holing prediction formula is proposed for the smoke exhaust vent with an additional baffle of the same size and an opening angle of 60°in the side smoke exhaust mode.The Froude number for the smoke exhaust with the additional baffle to have complete plug-holing is 13.87,and the exhaust air velocity is 5.34/5.93/7.71m/s when complete plug-holing occurs at5/10/15MW fire power.