Research On Operation Rules Of Drainage System For Utility Tunnel

The utility tunnel are public tunnels under the ground of city for the centralized laying of municipal pipelines for electricity,communications,radio and television,water supply,drainage,heat,gas,etc.It is a new form of transportation means,and the centralized management by various municipal pipelines integrated,can effectively improve the living standards of the people.However,the safe operation and maintenance of the utility tunnel is an important part of ensuring the safety of people’s lives and property,and its safety cannot be underestimated.Drainage system is a pillar to provide drainage safety in the affiliated systems of the utility tunnel.As far as the current domestic utility tunnels,the drainage system mainly includes sump,sump pump,stent of sump pump,drainage pipe and drainage canal etc.During the actual operation of the drainage system,excessive vibration of the pump,the decrease in the speed and pressure of the water flow in the drainage pipe,and a large number of vortices in the sump will seriously affect the working efficiency and reliability of the drainage system.It may even cause damage to the submersible pump and tremendous water accumulation in the utility tunnel.At present,rainstorms have a great impact on the utility tunnel.Among the 25 cities chosen in China,rainstorms have affected more than half of them.In the paper,the drainage system is simulated by computational fluid dynamics simulations and verified by the experiment.The research conclusions for the operation of the drainage system are proposed,which can provide a reference for the safety evaluation and design of the drainage system.In terms of computational fluid dynamics simulation of drainage system of the utility tunnel,the paper proposes a numerical simulation analysis model for drainage system fluid dynamics.The parameter calculation was done and the computational fluid dynamics model was established.Pre-processing tasks including simplification of the calculation model and compilation of the UDF function for the water flow rate were carried out.Firstly,the velocity field,pressure field and turbulent kinetic energy of the inner the drainage system were discussed under different working condition,which were the inlet velocity of water flow,the diameter of drainage pipe and the size of sump.The water flow in the sump can be divided into the disordered and stable states,that is,the prophase and stationary phase periods.For the velocity field,in the prophase period,the flow rate of the water can be kept constant firstly,and then in the horizontal and vertical transition areas of the water velocity decreased somewhat,and finally formed different velocity gradients near the pipe wall.In the stable period,the velocity of the area near the center of the drainage pipe was relatively small,while the velocity of the area near the pipe wall was relatively large.The mixing of the water flow field caused the formation of vortices,and under each operating condition,a low-speed area corresponds directly to the water intake.For the pressure field,the pressure at the corners of the left and right inner sides of the horn mouth was smaller than elsewhere,while the pressure near the water intake was greater than elsewhere.The larger space in the sump,the smaller the pressure fluctuated.The larger space in the sump,the closer value between the stable pressure and average pressure.It means the water pressure was easier to table at the average value,which can be used to roughly estimate the stable pressure value in the drainage pipe.The extent of pressure fluctuations was independent of the size of the sump.For the turbulent kinetic energy,the kinetic energy was concentrated at the water intake;the turbulent kinetic energy in the near-wall area was higher than the turbulent kinetic energy in the pipe when the water inlet velocity was zero;the larger size of the sump,the smaller the turbulent kinetic energy of the water body,which means a higher efficiency for the drainage system.And then the effect of the critical submersion depth of the sump pump on the operation of the drainage system was presented.Three empirical formulas under different working conditions were proposed.At last,compared with Heyun formula,Knauss empirical formula and Hecker empirical formula,the result showed that the relationship between the critical submergence depth and the Froude number approached Hecker empirical formula.In terms of the experiment of drainage system of utility tunnel,the paper provides a set of ideas and methods to test the drainage system.By means of the selection of sensors,submersible pumps,pipes,etc.,a test platform of drainage system was set up,and then a series of tests and experiments were done.Compared with the simulation results of computational fluid dynamics,it showed that the simulation results can better reflect the operation of the drainage system under rainstorm conditions.