Study On The Calculation Of The Transition Process Of The Pressure Diversion System Of Upstream Series Double Surge Chambers

For the hydropower station with super long diversion tunnel,the propagation time of water hammer wave in the upstream pressure pipeline is longer during the transition process.The double surge chambers system is built in the upstream,which can reduce the water hammer pressure.On the one hand,effectively solve the problem of hydraulic transition process,on the other hand,reduce the excavation amount of a single surge chamber,and improve the stability of surrounding rock and structural safety near the surge chamber.In this paper,combining with the project examples,a simulation model is established by using the characteristic line method to study the transition process of the pressure diversion system of upstream series double surge chambers.The conclusions are as follows:(1)In the process of large wave transition,increasing the size of the main surge chamber can reduce the highest surge water level of the main and auxiliary surge chamber,and accelerate the wave attenuation.There is a critical value of the impedance hole size of the main surge chamber.When the size is lower than this value,the highest surge water level of the auxiliary surge chamber decreases with the increase of the impedance hole size,and it rises when the size is higher than this point.If the size of the auxiliary surge chamber is too large,the sensitivity of the impedance hole of the main surge chamber will be weakened,which is not conducive to the wave attenuation of the double surge chambers.The location of the auxiliary surge chamber shall be close to the main surge chamber as much as possible.When the type of the auxiliary surge chamber is changed,the water hammer pressure and large fluctuation in the surge chamber do not change much.(2)In the process of small wave transition,increasing the size of the main and auxiliary surge chambers can reduce the highest surge water level of the double surge chambers and accelerate the wave attenuation.The quality of small fluctuation regulation can be improved by reducing the impedance hole size of the main surge chamber.The closer the position of the auxiliary surge chamber is to the main surge chamber,the better the regulation quality is.(3)In the process of hydraulic interference transition,the highest surge water level and output swing of the unit can be reduced by increasing the size of main and auxiliary surge chambers.Reducing the size of the impedance hole in the main surge chamber can improve the attenuation rate of fluctuation and reduce the output swing of the unit.The type change of the auxiliary surge chamber has little influence on the primary and auxiliary surge chamber and output swing of the unit.In a word,for the upstream double surge chambers system,the larger size of the main and auxiliary surge chamber and the smaller diameter of the impedance hole are conducive to the quality of small fluctuation regulation and the reduction of the output swing of the hydraulic interference unit,but the larger size of the auxiliary surge chamber is not conducive to the attenuation of the surge water level of the main and auxiliary surge chambers in case of large fluctuation.The critical point should be selected for the impedance hole of the main surge chamber.Too large or too small is not conducive to the large wave transition process.In order to meet the geological and topographical requirements,the location of the auxiliary surge chamber should be as close as possible to the main surge chamber,and the type of the auxiliary surge chamber has little influence on the transition process.