Trapped air pockets in liquid-filled piping systems may cause operational difficulties and may damage the system components. This lecture presents dynamic behaviour of trapped air pockets. Air trapped in the pipeline (along the pipeline, at high points and at devices) generates characteristic magnitude, shape and timing of unsteady pressure pulses. The severity of the hydraulic transient event is governed by volume, pressure and location of the trapped pocket. The theoretical model is based on unsteady liquid pipe flow equations. The trapped air pocket is modelled as internal or end boundary in dependence of its location. Two characteristic case studies are presented: (1) start-up event (flow acceleration from standstill condition) and (2) valve closure event (flow stoppage). There is a good agreement between the calculated and measured results for the two cases (start-up, closure); in particular, when the unsteady skin friction model is used in simulations.
F.18 Transfer of new know-how to direct users (seminars, fora, conferences)
COBISS.SI-ID: 17002779This report deals with water hammer analysis in HE Piva (Piva HPP (hydroelectric power plant)), Montenegro. The Piva is the peak HPP in the Montenegrin electro-energetic system with an installed capacity of 360 MVA. The simulated flow-passage system of the Piva HPP is comprised of the intake structure, followed by three parallel penstocks each with Francis type water turbine at the downstream end (including turbine inlet throughflow type butterfly valve). The outlet part starts with three parallel draft tubes that are connected to a common lower (downstream end) orifice type surge tank followed by tailrace tunnel and outlet structure. A description of water hammer computational method is given. The aim of this numerical analysis is to provide charts of the key transient quantities during emergency shut-down of the turbine(s). Emergency shut-down of the turbine unit is considered to be the most severe normal operating regime. The turbine is disconnected from the electrical grid followed by full closure of the guide vanes. A critical element is possible trapped air at the draft tube inlet and at tailrace surge tank. The resulting transient loads are controlled by appropriate adjustment of the guide vane closure manoeuvre.
F.17 Transfer of existing technologies, know-how, methods and procedures into practice
COBISS.SI-ID: 16973339