To investigate the transient characteristics and internal flow in the pipeline of pump system during regulating period of a valve, a onedimensional 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 threedimensional 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.
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