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Hydropower is an efficient renewable energy source able to regulate electrical grid fluctuations. However, many hydropower plants were built decades ago, and now it is the time for a major refurbishment. The turbine's efficiency is essential and needs to be determined before and after refurbishment. To this end, the flow rate needs to be determined. Amongst different discharge measurement methods, the pressure-time method is relatively inexpensive and easy to perform compared to other methods. In this method, the flow rate is estimated by the integration of the measured differential pressure and the pressure loss due to friction between two cross-sections in a conduit during the deceleration of the liquid mass by closing a valve or guide vanes. The pressure-time method's accuracy depends on how accurate the head loss and the integration endpoint are estimated. Furthermore, the pressure-time method has limitations specified in IEC-60041, which make it challenging to apply on low-head turbines due to the short water passages when the flow is developing. The main focus of work is to improve the accuracy of the pressure-time method and extend its validity for low-head turbine conditions. Numerical simulation and experimental study have been acquired. A CFD model is developed to investigate the effects of the endpoint of integration and friction models on the method's accuracy. The effect of different boundary conditions is studied in the CFD model, and the result is validated with available experimental data. Different frictional models used with the pressure-time method are compared with CFD simulation for the developing and developed flows. A new parameter is suggested to improve deviation related to the flow status; developing and developed. Furthermore, a new methodology is presented, where the flow rate is estimated with the pressure-time method function of several endpoints. Then, experimental investigations of the pressure-time method outside IEC-60041 recommendations for conditions similar to low-head hydropower are presented. A laboratory setup is designed and built to test the pressure-time method. The method is applied for cases with shorter length, smaller UxL, pipe with variable cross-section and shorter distance to irregularity than IEC-60041 recommendations. Different assumptions for calculating the pressure loss and dynamic pressure variation are studied. Moreover, the quasi-steady assumption's accuracy on the head loss estimation and the difference in dynamic pressure are compared with constant values for their coefficients. The systematic uncertainty of the pressure-time method is also calculated based on the Monte Carlo Method (MCM). |
