Flow Mechanism And Intelligent Control Strategies Of Fire Smoke In Corridor-Typical Adjacent Buildings

With the acceleration of urbanization,more and more buildings arise.In order to satisfy the growing needs of people,the building style is developing towards diversification and complexity.As an important building,the composite building structure is more in line with the real structure.However,the fire-related research of composite building is not sufficient compared with the single shaft structure and corridor structure.Based on numerical simulation,scaled experiment and theoretical analysis,this paper presented fire research of corridor-typical adjacent buildings,which mainly includes three parts:effects of ventilation state of vertical shaft on smoke migration behaviors in a corridor-shaft building;smoke movement and control strategy in typical room-corridor-atrium building under different boundary configurations;the intelligent smoke control system design and implementation based on real-time fire behavior.The specific findings include:A set of experiments was carried in a 1/4 scaled multi-layer building to investigate the effects of ventilation state on building fire.The results show that when the air supply parameters were small enough,the back-layering phenomenon arose obviously in fire floor,the boundary velocity at the end of the corridor remained uniform in the vertical direction.With the increase of air supply parameter,smoke spilled out from the fire floor and the thickness of the smoke layer gradually increased.At the same time,as the heat release rate increases,the air supply parameters required for back-layering flow were greater,and the larger the air velocity flowed into the corridor,the lower the smoke velocity overflowed to the outside.By analyzing fire-related parameters(smoke field,fluid velocity and temperature distribution),six typical migration paths were identified and validated by their corresponding experimental cases.The influence of ventilation state of the fire floor and the shaft on the transient and quasi-state characteristics of the flame were further analyzed.The multiple transitions of the transient flame were found in some cases.The quasi-state flame angle distribution could be divided into three stages:the fire floor ventilation dominate stage,the shaft ventilation dominate stage and the intermediate stage.And for the intermediate stage,the flame angle changed widely.Considering the impact factors of air supply pressure,stack effect and the pressure induced by the horizontal corridor smoke,a non-dimensional number,η,has been presented in this paper to identify the flame tilt direction for the multi-opening corridor-shaft composite building.When η is larger than 0.12,the flame tilts to the corridor,otherwise,the flame tilts to the shaft.As an important structure connecting rooms and atrium in large shopping malls,corridor certain has a huge impact on smoke movement but is rarely mentioned in previous studies.The purpose of this study is to investigate the impact of the corridor’s physical boundaries(corridor width and keep stand height)on the smoke characteristics within a typical corridor-atrium structure.A series of cases were carried out numerically by using Fire Dynamic Simulator(FDS).The results show that the existence of keep stand had a significant effect on the initial fire smoke migration path:the flue gas mainly spilled out from the near fire source when there was no keep stand or relative lower keep stand height;and the flue gas mainly spread to the atrium from the distant fire source when the keep stand was bigger enough.And for a certain HRR,there exists a critical corridor width,w0,the mass flow rate of spill edged plume and the temperature of the atrium reached the maximum.The higher the keep stand,the higher temperature and the height of the temperature field.And the temperature field also showed an asymmetric distribution due to the existence of the keep stand.The effect of exhaust vent position coupled with a physical boundary on exhaust efficiency was further analyzed.The results show that when the exhaust position is close to the outside corridor flank and the dimensionless height of the keep stand maintains at 0.375,the smoke exhaust efficiency reaches the highest.By introducing the keep stand height into the spill plume model,the modified model can well predict the mass flow rate.In order to overcome the effect of uncertainty fire scenario on a traditional smoke exhaust system,a new intelligent smoke control system was designed.The current system took each fire development stage into account and could make an intelligent adjustment to adapt the real-time fire and further to obtain the best smoke exhaust condition by overcoming unfavorable conditions.This system mainly included four parts:the design of the intelligent adjustment steps;parameters selection,sub-system design,and the system function implementation in CFD;CFD simulation and data analyses;system safety function evaluation.In order to reduce the influence of parameters fluctuation on system stability,a smoothing factor was introduced to eliminate the fluctuation noise.Besides,the effectiveness of the system was analyzed and verified.The results show that:compared with traditional methodology,the newly designed system provides a better fit for unpredictable fire scenarios.The intelligent system provided reasonable responses for different heat release rates,the larger the heat release rate of the fire,the larger the final activation step,and an exhaust velocity was obtained,and also the current system can also control a multi-stage heat release rate condition.The performance of the system was very flexible for different fire growth coefficients,and a time delay for each activation step occurred when the fire grew slowly.Furthermore,the fire growth coefficient had no effect on the final activation step,which was only determined by the peak heat release rate.An optimized condition was introduced to deal with the large scale or ultra-fast growth rate fire:a new constraint criterion was effective in solving the imbalance for a composite smoke control system.In general,the intelligent design system had the ability to make an optimum decision based upon the feedback of real-time fire characteristics and to ensure fire safety for different kinds of fire.