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)

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

Wielokryterialna optymalizacja wytwarzania energii w wieloblokowych elektrowniach wodnych

Maintaining variable operating conditions of water barrage, imposed upon the owners of hydroelectric power plants by various acts and administrative decisions, requires proper adjustment of power plant water discharge by variable opening of turbine control components. This changes the generated power and thus shifts the hydro units operating point, which alters the power generation efficiency. In power plants equipped with two or more hydro units, it is possible to configure operation of hydro units and load each of them with such active power as to obtain the best possible electrical energy generation efficiency with the available hydroelectric potential of the barrage. In this paper, the method of optimising an example multi-unit hydroelectric power plant using various criteria was described, i.e. the efficiency criterion or the revenue criterion. Particular attention was paid to the maximisation of generation efficiency to ensure the maximum use of the inflow and head available at the barrage under the restrictions due to current conditions.Dotrzymanie zmiennych warunków użytkowania stopnia wodnego, narzuconych właścicielom elektrowni wodnych w różnego rodzaju aktach i decyzjach administracyjnych, wymaga odpowiedniego dostosowania przełyku elektrowni poprzez zmianę stopnia otwarcia elementów regulacyjnych turbin. Skutkuje to zmianą generowanej mocy i tym samym przesunięciem punktu pracy hydrozespołów powodującym zmianę sprawności wytwarzania energii. W elektrowniach wyposażonych w dwa lub więcej hydrozespołów można tak dobrać konfigurację pracujących hydrozespołów i każdy z nich obciążyć taką mocą czynną, aby uzyskać najwyższą możliwą sprawność wytwarzania energii elektrycznej z dostępnego potencjału hydroenergetycznego stopnia wodnego. W artykule opisano sposób optymalizacji przykładowej wieloblokowej elektrowni wodnej z wykorzystaniem różnych kryteriów, tj. kryterium sprawnościowego czy też przychodowego. Szczególną uwagę poświęcono zagadnieniu maksymalizacji sprawności wytwarzania gwarantującej maksymalne wykorzystanie dopływu i spadu dostępnego na stopniu przy narzuconych ograniczeniach wynikających z aktualnych uwarunkowań

Discharge measurement and performance tests of hydraulic units in low-head small hydropower installations

In course of over half a century the test teams of the Szewalski Institute of Fluid-Flow Machinery (IMP PAN) have conducted numerous performance tests of small hydropower (SHP) installations on various occasions and motivations, including updating or establishing performance characteristics of old machines, acceptance of new units, checking or optimising the cam correlation of new or refurbished double-regulated turbines, checking performance of prototype turbines under field conditions. The discharge measurement techniques have included currentmeter, pressure-time and acoustic methods. Index tests, using the Winter-Kennedy and other differential pressure methods, as well as current-meter and acoustic techniques, have been employed quite frequently to optimise the cam curves of double-regulated machines. In one case a simplified technique based solely on the power/wicket gate opening relationship was checked. This paper discusses some techniques applied when determining the absolute efficiency and optimizing cam correlations by means of absolute and index test methods. Cubic spline formulae as applied to integrate the flow velocity field in a hydrometric section are derived. Results of a discharge measurement by means of the current-meter and pressure-time method are compared as a special case study. Finally, practical recommendations addressed both to the power plant owners and the test team members are formulated