An extension of the momentum transfer model to time-dependent pipe turbulence

We analyze a possible extension of Gioia and Chakraborty's momentum transfer model of friction in steady turbulent pipe flows (Phys. Rev. Lett. 96, 044502 (2006)) to the case of time and/or space dependent turbulent flows. The end result is an expression for the stress at the wall as the sum of an steady and a dynamic component. The steady part is obtained by using the instantaneous velocity in the expression for the stress at the wall of a stationary flow. The unsteady part is a weighted average over the history of the flow acceleration, with a weighting function similar to that proposed by Vardy and Brown (Journal of Sound and Vibration 259, 1011 (2003); ibid. 270, 233 (2004)), but naturally including the effect of spatial derivatives of the mean flow, as in the Brunone model (B. Brunone et al., J. of Water Resources Planning and Management 236 (2000)).Comment: 15 pages. 2 figures (included) arXiv admin note: text overlap with arXiv:1005.040

Flow rate measurements under operating conditions of hydraulic machines

Przedstawiono wybrane zagadnienia zdobyte w ostatnich latach w metodyce pomiaru natężenia przepływu w warunkach eksploatacyjnych lektrowni wodnych. Doświadczenia dotyczą kilku metod klasycznych - metody młynkowej, wolumetrycznej, Gibsona i Winter-Kennedyčgo. Gółwną uwagę zwrócono na zagadnienia nie ujęte w odpowiednich normach międzynarodowych oraz wskazano na wpływ stosowania technik komputerowych (do akwizycji i analizy danych pomiarowych) na poprawe jakości pomiaru.Chosen experiences gained during the last decade in the flow rate measurements in service conditions of water powerplant by the classic methods (the current-meter method, volumetric method, pressure-time (Gibson) method and Winter-kennedy method) are presented. The main attention is paid to problems not taken into consideration by international standards. The influence of using computer technique on improving quality of measurements is also shown

Modifications of the flow rate calculation procedures in the application of the pressure-time method and the current meters method in hydropower plants

Metody uderzenia hydraulicznego i młynków hydrometrycznych są najczęściej używane do pomiaru natężenia przepływu podczas badań energetycznych turbin wodnych. Liczne doświadczenia w stosowaniu ww. metod pomiaru były przesłanką do wprowadzenia nowych elementów, które udoskonalają sposoby całkowania zmierzonych wielkości w procedurach obliczania natężenia przepływu. Modyfikacje te mają na celu poprawę dokładności pomiaru natężenia przepływu rozważanymi metodami.The hydraulic current meters method and pressure-time method are most commonly used in measuring of the hydraulic turbines. Gained experience in application both mentioned methods in flow rate measurements was basis for the introduction into them new elements that are supposed to improve the accuracy of integration of the measured values. For the pressure-time method, in comparison to the IEC 60041 standard, the calculation procedure has been changed by introducing modifications that concern: (1) the procedure for calculating the hydraulic losses, and (2) determining the upper limit of integration. For current meter method, the calculation procedure has also been changed by introducing modifications that concern: (1) the boundary layer calculated by means of von Karman formula in which some parameters have been introduced instead of the recommended by the ISO 3354 standard, and (2) the way of integrating of the measured velocity field in which NURBS have been applied that allow to avoid some improper shapes of the interpolated profiles. New procedure is compared with other procedures – (1) compatible with ISO 3354, and (2) based on the natural cubic splines. Assessment of the two modified methods was based on the results of the simultaneous flow rate measurement in Polish hydropower plant equipped with Kaplan turbines with penstocks (Fig. 5). The comparison of the results confirmed the validity of new elements introduced to the procedures (Fig. 6)

Consideration of the Cavitation Characteristics of Shut-off Valves in Numerical Modelling of Hydraulic Transients in Pipelines with Column Separation

AbstractThe paper presents the results of calculations of the water-hammer course accompanied by the column separation caused by a rapid closure of the butterfly valve. The computational method takes into account the cavitation characteristics of the valve that has been determined on the special laboratory stand in the Szewalski Institute of Fluid-Flow Machinery in Gdansk, Poland. In addition, calculations have been conducted using authors’ own discrete-vapour-cavity-model (the New Single-Zone DVCM). The paper presents also a comparison between these calculation results and the experimental ones obtained at the own laboratory stand for investigation of the water-hammer phenomenon in the pump discharge pipeline. The comparison of the numerical and empirical results is a basis for the verification process and assessment of the computational method that has been developed

A new approach to using the classic pressure-time method of discharge measurements

Discharge measurement using the pressure-time (Gibson) method typically involves mounting measurement instrumentation on the outside of the penstock. In the case of a hydropower plant where the penstock is built over concrete, an innovative approach is necessary in order to install instrumentation inside the penstock. Such instrumentation has been implemented for the purpose of efficiency tests of the upgraded small Kaplan turbine. The pressure-time method, in its classic version, requires sending pressure signals from both penstock cross-sections to the differential pressure transducer by means of connecting tubes. This raises the question on the influence exerted by dynamic properties of the connecting pipes/transducer system on the discharge measurement results. Calculations carried out using previously developed method enable authors to demenstrate that the connecting pipes/transducer system had exerted a negligible influence on the discharge measurement results

Method for calculating performance characteristics of hydrokinetic turbines

This paper presents a numerical algorithm and its computer implementation (program) developed to determine the operational characteristics of axial flow hydrokinetic turbines. The program is based on the Vortex-Lattice Method (VLM), which proved useful for predicting hydrodynamic characteristics of screw propellers. In order to validate the software, we carried out a series of experiments on a laboratory test stand at the Institute of Fluid-Flow Machinery at the Polish Academy of Sciences (IMP PAN) in Gdansk. From the practical point of view, the agreement between the calculated and experimental results was satisfactory. Therefore, the developed numerical method can be a useful tool for the analysis of operating conditions and in the design of hydrokinetic turbines