Fluid transients and wave propagation in pressurized conduits due to valve closure

Abstract

Transient analysis of the pipe flow is often more important than the analysis of the steady state operating conditions that engineers normally use to withstand the additional loads resulting from instantaneous rapid valve closures. The flow rate and fluid pressures in the system may change from significantly high to an extremely low magnitude after some time interval of valve closure. These types of unsteady flows are frequently encountered in sudden closing of upstream valve of a turbine in hydroelectric power station. The governing equations of unsteady flows in closed conduits are partial differential equations of hyperbolic type. One simple numerical solution technique available in the literature is the method of characteristics (MOC). In the current paper, the MOC model is explained through one case study of valve closure. One bench mark problem of reservoir on upstream end and a valve on the downstream of pipeline end is demonstrated in this paper. Fluid pressure and flow rate variations in pipeline with respect to time after the valve closure are arrived from MOC model. It is observed that pressure head increased after development of first pressure wave which is due to instantaneous closure of the valve at the downstream end of the pipe. The pressure head and flow rates are not dampened but they were found to be oscillating by increasing and decreasing in the total simulation time which may be due to wave propagation time and consideration of series pipe of different diameters in the current study.