Skin friction and consequential damping in unsteady flows can significantly reduce the harmful effects of some pressure transients and it can have a strong influence on system behaviour close to resonance. Experimental data for the validation of theoretical models of unsteady skin friction are limited. There is a need for a wider range of well-controlled unsteady flow regimes and detailed visualization of flow structures and profiles. A large-scale pipeline apparatus at Deltares, Delft, The Netherlands, has been used for unsteady skin friction experiments in acoustic resonance tests. In addition to standard instrumentation, two distinctive instruments have been used: hot-film wall shear stress sensors and a PIV set-up for measurement of unsteady flow profiles. Pulsating flow tests have been performed with an average flow of Reynolds number 22,000. The frequency of oscillation varied between 1.5 and 100 Hz. The wall shear stress at resonance conditions is about two times higher than at non-resonance conditions. The shape of the velocity profile at non-resonance conditions is similar to the shape in steady state flow. The shape of the velocity profile at resonance conditions is a typical unsteady state velocity profile including pronounced reverse flow and forward flow maxima near the pipe wall.
F.18 Transfer of new know-how to direct users (seminars, fora, conferences)
COBISS.SI-ID: 13186075A pressure relief valve (PRV) is a hydro power plant safety device whose operation is synchronized with turbine regulation (wicket gates) in order to prevent excessive pressure rise in the water conveyance system due to water hammer event. The PRV valve rapidly diverts the water flow away from the turbine into a turbine bypass system when the wicket gate apparatus needs to close suddenly at emergency shutdown (system fault) or when the unit is quickly unloaded (load reduction). The PRV is not a standalone device. It is part of the energy dissipation system (EDS) which consists of the inlet collector pipe, the PRV valve, the dissipation chamber and the connecting channel to the tailrace. In addition, the energy is dissipated in water conveyance system due to skin friction and in the turbine itself (turbine dissipation mode). For a very long penstock, the skin friction losses can be significant. For relatively slow transients, the steady state approach is adequate and this is traditionally used in industrial water hammer packages. The paper focuses on energy dissipation methods that have been and will be designed and manufactured by company Litostroj Power.
F.17 Transfer of existing technologies, know-how, methods and procedures into practice
COBISS.SI-ID: 13185051