The Transient Numerical Simulation Of Pressure Tailwater In Sewage Treatment Plant And Its Application

The damage of water hammer affects the safety of pressure pipeline directly.Sewage treatment plants have sprung in recent years.With the long distancetailwater transportation becomes main way of draining,the damage caused by waterhammer ensues.Tailwater pipes and water pipes are both pressure pipes and target tothe free boundary.Compared with the water supply system,which targets to anon-free boundary,they take less risks to have a water hammer accident.For thereare aeration processes in the treatment,tailwater dissolves more air than watersupply system. The air in water brings more uncertainty to the water hammerphenomenon. It is necessary to discuss if the traditional measurement to relieve thedamage of water hammer is suitable for the special case of tailwater.In this paper,a numerical simulation of a certain project is performed under thehelp of the one-dimensional software Flowmaster and the three-dimensionalsoftware Fluent. Conclusions are made to show the pressure change of the pipeunder different working conditions.The processes under the conditions of differentair valve diameters and arrangements and the volume fraction of air are simulated toreveal the influence of these factors on the volume of cavity and water hammerpressure.The conclusions of the paper have shown that the power cut of all pumps leadsto a maximal pressure change in the system without air valves,while the conditionthat one pump powers on&off with another running at a constant rate lead s to amaximal pressure change in the system with air valves. The more pumps run,the lessinfluence one pump would make.Under no circumstances does the variablefrequency condition affects the pressure change more notable than otherconditions.The cavity volume in the convex slope pipe reaches a peak when the airvolume fraction of the inlet water is2‰.When the air fraction increases,it is fasterto consume energy to a steady state,due to the air cushion caused by evolution.Butwith the interception air-mass, current rush will bring an unexceptional pressure lift.The relationship between gas content in the water hammer with gas and waterhammer pressure has to be concluded after an all-around calculation and discussion.The optimized application of air valve and other measures is proposed in a realproject.The method of the study is suggested to apply in the simulation of similarprojects as a reference.The result of the study provides a technical support in the design of a tailwater pipeline,and it is useful in the promotion of the tailwaterpipeline study.