Numerical Simulation Of Internal Flow Mechanism Of Compound Air Valve

The compound air valve is a very necessary water hammer protection measure.By arranging the compound air valve in the proper position in the water conveyance pipeline,the occurrence of water hammer accident can be avoided or reduced,thus realizing the continuous safe operation of the water conveyance pipeline.By means of numerical simulation,the exhaust process of DN100 compound air valve under high-speed exhaust state,the gas-liquid two-phase flow and the gas-liquid two-phase flow interact with the sphere in the DN100 compound air valve under the closed and sealed state,and the haling process of the compound air valve under negative pressure and the air interact with the sphere in the compound air valve under the negative pressure state is studied in this paper.In addition,the micro-outlet diameter of the compound air valve was optimized and analyzed.The main contents and achievements of this paper are as follows:(1)According to the calculation of hydraulic transient process of Beidanche pumping station in Shanxi Province under different working conditions,it is concluded that the combined protection of hydraulic butterfly valve and compound air valve in the two stages of pump stop can significantly improve the positive and negative pressure of the pipeline and make it meet the requirements.(2)Under the high-speed exhaust state,different exhaust pressure differences are set for numerical simulation.It is concluded that with the increase of exhaust pressure difference,the average outlet flow rate gradually increases.(3)Under closed and sealed state,the gas-liquid two-phase flow and fluid-structure interaction are numerically calculated respectively.The conclusions are as follows: 1)Vortexes appear in the velocity flow field on the middle plane and mainly distribute around the sphere;2)The maximum pressure of gas-liquid two-phase flow on the middle plane is positively correlated with the inlet velocity;3)The turbulence intensity is low in areas where gas phase is easy to collect;4)With the increase of inlet speed,the maximum deformation on the outer surface of the sphere increases gradually.(4)Under the negative pressure state,different intake pressure is set for numerical simulation.It is concluded that with the increase of inlet pressure the maximum deformation on the outer surface of the sphere increases gradually.(5)Taking the average flow velocity of the outlet as the maximum as the goal,the optimal diameter of micro outlet of DN100 compound air valve is sought by numerical simulation method,and the optimal value is 14 mm within the range of 3-24 mm.The internal flow field characteristics of DN100 compound air valve under the diameter of the micro exhaust port are further explored.The conclusion is that the area where the change of air velocity and pressure is concentrated in the junction between the micro exhaust port and the valve body.(6)The internal flow mechanism of the compound air valve under the above states provides technical basis for engineering application and optimization design of the compound air valve.