Influence Of Slope And Obstacle On Gas Leakage And Explosion Of Utility Tunnel

At present,the research on safety protection measures and engineering design technology of urban underground space engineering has begun gradually.Although the state has issued the relevant technical specifications for the comprehensive utility tunnel,supplementary regulations can be made for the possible accidents in the future.At present,the comprehensive utility tunnel with large slope is under construction.Obstacles such as pipeline supports in the pipe gallery structure will also affect the gas explosion process.It is necessary to analyze the influence of slope and obstacles on the gas leakage and gas explosion process in the utility tunnel,so as to supplement the design specifications and provide guidance for properly working of the utility tunnel suggestions.Taking the comprehensive utility tunnel of gaotangping Road(phase II)in Changsha City as the research object,the process of small hole leakage in the gas tank from normal ventilation to alarm response switching accident ventilation is analyzed by CFD software with different longitudinal slope,and the law of gas leakage diffusion is analyzed.After verifying the feasibility and reliability of the numerical model,the related problems of gas explosion in the corridor with obstacles are simulated and analyzed by CFD software.The results show that:The diffusion direction of gas leakage is related to the slope and ventilation direction.After the accident ventilation,the diffusion direction is the same as the ventilation direction,and the diffusion speed is positively correlated with the gradient when the distance is more than 30 m from the leakage port.Before the ventilation status in the cabin is not switched,the methane cloud in the downwind direction of the leakage port is distributed in half "jellyfish" state,while the upwind direction is irregular.The alarm response is completed in different ventilation direction and different slope conditions within 10 seconds after leakage.With the same ventilation direction,the greater the slope,the shorter the alarm response time.According to the response time of the first two alarms,the location of the leakage source can be preliminarily determined under each slope.Therefore,for methane alarm arrangement,it is suggested that the layout height on the side wall can be appropriately reduced with greater slope.The premixed gas in the natural gas cabin of the comprehensive pipeline gallery will pass through the laminar flame propagation stage,turbulent flame acceleration stage and flame deceleration stage affected by shock wave oscillation.During the explosion of methane air premixed gas in cabin,the combustion wave will rapidly increase the temperature of each monitoring point through the way,and the rising law of flame temperature at each point will be close to the same.After the obstacle is arranged,the starting time of the temperature rise around the obstacle will be advanced,and the maximum temperature peak will be increased.When there are two obstacles in the cabin,the peak temperature is the largest,twice the value of the barrier free cabin.The temperature difference of the monitoring point before and after the cross section is obvious,which is between 400 k and 500 K.In the case without obstacle,the peak overpressure was 0.69MPa;after the mesh barrier was arranged,the peak overpressure increased significantly,and the peak overpressure increased by 62% and 141% after the obstacle was placed on one side and two sides of the ignition source.After the obstacles are arranged,the time of overpressure increase is also advanced.In the process of gas explosion,the overpressure characteristic curve of each monitoring point will have a double peak phenomenon.With the distance from the ignition source getting farther,the interval time difference between the two peaks of each monitoring point will increase firstly and then decrease,while the two overpressure peaks will fluctuate to a certain extent,and the total will show an upward trend.The time difference between the two peaks will reach the maximum at 20 m away from the ignition source,and the maximum time difference between the two peaks will appear at 50 m away from the ignition source after placing obstacles.The maximum time difference between the two peaks will be significantly reduced if the cabin structure is symmetrical.