闸阀调节过程的三维模拟及其动态模型

3D simulation and transient model for regulating period of gate valve

为了研究泵系统调阀过程的瞬态特性和内流机理,在一维分析软件Flowmaster中建立了包含管路、阀门和泵在内的仿真模型,并以三维简化闸阀为模型,采用Fluent 6.2进行计算,对开启过程的非定常内部流动进行数值模拟研究.采用动网格的方法分析了阀门开启过程中阀芯运动引起的流场变形.结果表明:直线特性和对数特性的调节阀都具有快开特性,即流量变化对阀门的相对开度相当敏感,当阀门开度为10%～20%时,水击压力迅速下降;而通过内部流态分析可知,在阀门开度较小的工况下,阀后流场紊乱,造成较大的水力损失,使阻力系数值增加,当阀门开度小于50%时,稳态和瞬态工况下阀门的阻力系数值有较大的区别.由分析可知,研究阀门开启过程的瞬态特性,以及建立内部流态模型,都不能完全按照通常的稳态理论进行,尤其对阀门开度较小的工况,应对其进行一定程度的修正,以保证计算结果的正确性.

To investigate the transient characteristics and internal flow in the pipeline of pump system during regulating period of a valve, a one-dimensional simulation model which contains the pipes, pump and valves etc has been established by software Flowmaster. CFD code Fluent 6.2 was used to solve the incompressible three-dimensional transient turbulent N - S equations with the dynamic mesh method to deal with the moving boundary caused by the opening valve core. The simulation results show that the valves with linear and logarithmic regulating characteristic have a fast opening feature which means the flow rate is very sensitive to the valve opening degree, in addition the water hammer pressure falls down promptly when the relative opening degree is in the range of 10% to 20%. As the valve relative opening degree is reduced, the flow behind the valve becomes disorder, leading to great hydraulic losses and considerable drag coefficient. For instance, the drag coefficient of valve under transient period shows great difference from that under static condition when the relative opening degree is less than 0. 5. These analyses show that the transient behavior and unsteady internal flow pattern cannot be handled by the existing usual analytical steady flow models during regulating period of a valve, especially at a relatively small opening degree. In that case, the steady flow models are subject to be amended in some degree to allow them to provide correct computational results.