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Pump running in turbine mode: state-of-the-art, prediction method, performance study and frequency analysis of the pressure pulsations

par Abeyo Mayo Tchada, Vo
Président du jury Parente, Alessandro
Promoteur Hendrick, Patrick
Publication Non publié, 2025-08-21

Thèse de doctorat

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Résumé :

Interest of Pump-as-Turbine (PaT) is growing with diverse applications in engineering. Usually, the data of PaTs are not available in the hands of pump manufacturers. Therefore, performance prediction methods appear as an important research area of PaTs. The current prediction methods rely on expensive, inaccurate and time consuming experimental methods. In the scope of this work, a robust prediction method is built up for a centrifugal impeller PaT. The most significant hydraulic losses were derived in PaT mode, these are namely, the shock losses at the impeller inlet, the swirling losses at the impeller outlet and the impeller wall frictional losses. The Euler head, the available total head and the hydraulic efficiency were computed as well. The global efficiency was computed taking into account the machine mechanical and volumetric efficiencies, enabling therefore to perform comparison of the new prediction method with experimental, Computational Fluid Dynamic (CFD), and the Rossi+Yang prediction methods. From where it resulted a good agreement between the given prediction methods over the full range of operations, confirming the robustness and the applicability of the proposed prediction method. The relative difference between the new prediction method and CFD data and between the new prediction method and experimental data remained higher for lower discharge conditions, notably in extreme part-load conditions, where a small error could result in very high relative difference.This work has also addressed the research problematic of PaT performance improvement. The sharp impeller (original impeller) leading edges was identified as detrimental in PaT mode. The performance of the rounded and the original impeller leading edges were studied by CFD method carried out on ANSYS CFX. Although the impeller leading edges rounding has notably increased the global efficiency in part-load conditions, the difference of global efficiency between both impeller types was decreasing when increasing the discharge. The hydraulic head generated by the rounded impeller leading edges was also slightly higher at part-load conditions, but when increasing the discharge, the difference between both heads became negligible. It appeared from numerical simulations that the impeller leading edges rounding allows to decrease the hydraulic losses of the individual sub-domains except the outlet pipe. For the seek of a comprehensive analysis, the significant losses were computed for both impeller's geometries. It was observed that the shock losses and the swirling losses of the rounded impeller leading edges were lower at part-load conditions, but when increasing the discharge, both losses were lower for the original impeller's geometry. The rounded impeller leading edges exhibited as well lower wall frictional losses for the full range of operationsIn order to investigate the influence of geometry modification on the operational safety as well as on the flow physics, a frequency analysis of the pressure pulsations within the flow domain was performed on both PaTs. In that respect, transient numerical simulations of severe part-load condition were processed for 5 rotations of the impellers, only the last rotation was considered for analysis. Pressure monitoring points were positioned within the volutes, the impellers and the outlet pipes of the two investigated impeller PaT models. Among both impeller's geometries, the original impeller PaT pressure pulsations frequencies were generally found at frequencies integer of the Blade Passing Frequency whereas the rounded impeller PaT pressure pulsations frequencies were generally found at frequencies integer of the impeller passage frequency, confirming the influence of Rotor-Stator Interaction (RSI) on the given geometries. For both PaTs, the main frequency was generally found at the Blade Passing Frequency, except for the outlet pipe of the rounded impeller PaT and the monitoring point right close to the volute inlet of the original impeller where it was respectively found at the impeller passage frequency and one of its harmonic. Moreover, the highest pressure pulsation amplitude among both geometries was found for the original impeller PaT, close to the middle zone of the inter-blade flow channel.