The Research Of The Harmful Gasdistribution And Motion Characteristics In Sewer System

As the city size growing bigger and bigger, the security of the sewer is becoming more and more important. This paper haveresearched the harmful gasdistribution and motion characteristics in sewer system and verifythe Accuracyof using the CFD simulation technology to calculate the sewer dropshaft. Calculate the head fall in the inspection shaft, and get the corresponding characteristic curve of the equivalent fan.We can accurately assess the ventilation status in sewer system by unit the characteristic curve of the equivalent fan and the pipe resistance characteristic curve. Use infinitesimal method to build the sewer gas moving and distribution model and get 3 type gas distributed state, and the main Conclusion as follows(1)It is practicable to use the math model to calculate the Ventilation in sewer, the manhole have a bigger gas flux which close to the dropshaft(2)Generally speaking, the dropshaft hole is air inflow, mean that, the fresh air will enter the sewer through droshaft,the hole will have a smaller flux which far away it.(3)By contrast with the model experiment results, The average error by VOF model is 7.43%,and the biggest error is 12.5%, so it is can be considered that it is viable using the VOF model to calculate the ventilation of dorpshaft in sewer(4)When the manhole opening ratio is 0.125%,0.5%,1% and 100% in DN800 pipeline, the sewer safety length will be 246 m,626m,705 m and 741m。appropriateincreasethe opening ratio will significant increasethe safety length.But when the opening ratio is big enough, continue increasing the opening ratiowill help less.(5)Use infinitesimal method to build the sewer gas moving and distribution model and get 3 type gas distributed state: gradually smaller, gradually bigger and climb up and then decline.