Numerical analysis of the hydraulic transient response in the presence of surge tanks and relief valves


Performance of surge tanks and relief valves on the unsteady flow in the penstock is studied.

A CFD model based on the dynamic friction is proposed to investigate the unsteady flow problem.

Surge relief valves can be used in place of surge tanks to improve the transient response.

Herein, the turbine over speed is 155% of the nominal speed when no protective device is installed.


Water hammer as a critical consequence of unsteadiness may take place in the penstock of the hydroelectric power plants. Hence, the unsteady flow analysis is important to identify undesirable pressure variations and to take preventive actions toward guaranteeing safe operation of the power plant. Chief among these actions are the installation of a surge tank and relief valve, and the transient flow behavior in the presence of protective devices is investigated herein. The method of characteristics is employed to numerically solve the equations governing the transient flow through channels. Also, in order to better resolve the transient behavior, unsteady friction effects have been considered. Validation of the developed computational code is carried out through comparison of the computed transient pressures with those measured at Karun-III Hydropower Plant. According to the results obtained for MONJ Hydropower Station, when only one turbine is in operation, the surge tank decreases the pressure rise within the spiral case and the turbine overspeed by 22% and 6%, respectively. While the percentages associated with employing a proper surge relief valves are accordingly 12% and 14%. This study substantiates how surge relief valves can be used instead of an expensive surge tank to relieve the transient response.


  • Hydropower plant;
  • Hyperbolic PDE;
  • Relief valve;
  • Surge tank;
  • Transient flow;
  • Unsteady friction

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