空气阀水力瞬变数学模型

空气阀是输水管道系统常用的防止水击破坏的智能化安全设备。针对目前空气阀水力瞬变数学模型假设气温T为常数及忽略空气阀高度影响的问题,首先基于等熵流动的气动力学理论,提出了新的空气阀进排气基本方程,然后,把空气阀、配套检修阀和连接管用一个具有自动进排气功能的调压室等效,提出了新的空气阀水力瞬变数学模型及其求解算法。与现有空气阀水力瞬变数学模型相比,在不考虑空气阀高度的条件下,新模型计算的最大水压更大,而负压也更低,这意味着以现有模型计算结果作为设计依据存在安全风险。考虑空气阀高度后,计算的输水管最大水压减小,但是负压也更加严重,因为等效调压室内水体对进排气有阻止延缓作用。此外,以空气阀气体为绝热流动所得计算结果作为设计依据是合理的,偏于安全的,因为在这种情况下计算的最大水压较大而最小水压较小。

Mathematical models for hydraulic transients of air valves

Air valve is an intelligent safety device commonly used in water pipeline system to prevent water hammer damage.In view of the problem that the air temperature T is assumed to be a constant in the current hydraulic transient mathematical model of air valves and the influence of air valve height is ignored,new basic equations of air valve inlet and outlet are proposed based on the aerodynamic theory of isentropic flow.Then,a new hydraulic transient mathematical model of air valves and its solution algorithm are proposed by equating the air valve,the supporting maintenance valve and the connecting pipe with a surge chamber with automatic air inlet and outlet functions.Compared with the existing hydraulic transient mathematical model of the air valve,the maximum water pressure calculated by the new model is higher and the negative pressure is lower without considering the height of the air valve,which means that there is a security risk based on the calculation results of the existing model as the design basis.After considering the height of the air valve,the calculated maximum water pressure decreases,but the negative pressure is also more serious,because the water in the equivalent surge chamber can prevent and delay the intake and exhaust.In addition,it is safer to use the calculated results of the adiabatic flow of air valve gas as the design basis,because the maximum water pressure calculated in this case is larger and the minimum water pressure is smaller.