| With the development of China’s social economy,the pressure of urban traffic is increasing.In order to solve the problem of traffic travel,urban rail transit quickly stands out.Metro has become the main force of urban rail transit,and fire is one of the biggest factors that endanger the safe operation of metro.In order to provide favorable conditions for evacuation,ventilation and smoke exhuast system must be opened.In this paper,using the method of model experiment and numerical simulation,the flow field of tunnel ventilation and smoke exhaust under different fan combinations is studied,and the best fan combination ventilation and smoke exhaust system is selected.The research results are of great significance for the design of ventilation and smoke exhaust system and personnel evacuation of long and large metro tunnel.Based on the model similarity theory,a 1:10 scale tunnel ventilation and smoke exhaust model with a total length of 20 m is built.The tunnel ventilation and smoke exhaust experiments under four different fan combinations were carried out.The real-time monitoring of the flow parameters in the tunnel was carried out by using sensors and console.The variation of fan power consumption,velocity on both sides of the carriageway,static pressure and velocity on both sides of the smoke exhaust duct with the increase of fan frequency was analyzed.Model experiments were carried out for four kinds of fan combination ventilation and smoke exhaust modes,and it was found that the static pressure of the carriageway of the ventilation and smoke exhaust system was symmetrically distributed with the smoke ceiling vent as the center under the critical smoke exhaust state regardless of the fan combination mode.Secondly,the phenomenon of smoke flow under the exhaust port was observed in the experiment,and it was found that the airflow stagnation effect was the key factor affecting the exhaust effect of the smoke ceiling vent.Furthermore,by fitting the curves of combined overall power consumption and carriageways’ velocity,combined power consumption and carriageways’ static pressure,the relationship between power consumption and carriageways’ static pressure and velocity is analyzed.Then,the formula is derived and the dimensionless Euler number is proposed to quantify the performance of airflow stagnation effect;After substituting the four kinds of combined data into the formula,it is concluded that the TPTE（Two Pressing-in fans + Two Extracted-out fans）is the optimal ventilation and smoke extraction condition.Secondly,the TPOEL（Two Pressing-in fans + One Extraction fan on the Left）on the same side of the extraction fan and the disaster point of the carriageway is the optimal three fan combined ventilation and smoke extraction system.Finally,according to the structural parameters of the tunnel prototype,a full-scale tunnel numerical model with a length of 120 m is constructed.After the completion of mesh generation,the numerical simulation of tunnel ventilation and smoke exhaust under multiple working conditions is carried out.Comparing the results with the model test results,the error values of four groups of TPZE（Two Pressing-in fans + Zero Extracted-out fans）conditions are6.09%,5.66%,4.67% and 4.95% respectively,which proves that the model experiment and numerical simulation are scientific.The velocity and static pressure nephogram of tunnel cross section under different working conditions are analyzed,and the streamline diagram is used to explain the fluid phenomenon.The numerical simulation results clearly show the phenomenon of airflow stagnation effect,and it is found that there is surrounding flow under the smoke ceiling vent.Through the model test and numerical simulation,the study of tunnel ventilation and smoke exhaust under the condition of single smoke ceiling vent is carried out,and the relevant conclusions can be used as an important reference for the optimization of ventilation system design and the formulation of emergency plan for tunnels,which is helpful to formulate reasonable fan combination strategy and power consumption selection,evaluate the efficiency of ventilation and smoke exhaust system,and improve the disaster reduction and disaster relief ability of tunnel ventilation and smoke exhaust system. |
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