This diploma thesis deals with centrifugal pump running as a turbine. Basic working principles of a pump are included, both in pump and turbine regime. Experimental data obtained from laboratory test bed are compared with CFD simulation on slightly simplified geometry. Obtained results are then processed using spectrogram. Influence of time step and mesh size on results is also researched.

In the last decade, the power generation mix and the energy markets have been affected by the growing development of distributed and renewable energy sources.Nevertheless, a significant drawback of solar and wind energy is their intermittent and weather-dependent production, which often leads to a mismatch between renewable energy production and its use. Thus, the need for energy storage is recently emerging and becoming more relevant in this era of the energy transition. Among several technologies, today, pumped hydro energy storage (PHES) represents the largest share of the energy storage systems in the world. However, possible new investors, who might be attracted by potential profit in PHES, are repelled bythe long payback period and the scarcity of adequate site topology for such power plants. Relevant design decisions can be taken to reduce the costs and improve the performance or to escape the PHES topographical requirements. For this reason, the first part of this PhD thesis reviews and provides potential assessments of some unconventional PHES systems, applied in synergy with existing infrastructures. Such is the standpoint of micro facilities near waterway locks, or underground cavities used as lower reservoirs (UPSH), or the use of pump-turbines at variable geometryto cope with fluctuating loads.Moreover, important information on PHES in micro-scale is largely missing and their potential in distributed energy systems still needs to be unveiled. In the attempt to fill this gap, this thesis provides a techno-economic overview of the design and characterization of a first-of-its-kind PHES micro facility. In micro-scales hydropower projects, the initial capital cost of a conventional hydroelectric unit is hard to be determined and often economically prohibitive. Interestingly, in order to cut the total capital investment, the micro-PHES prototype runs with a single centrifugal pump for both pumping and generating phases and exploits existing stormwater reservoirs. The variable speed regulation is also implemented and it allows the pump to constantly operate at the maximum hydraulic efficiency in order to deal with load variations. In the same way, the pump working in reverse, namely pump as turbine (PaT), runs at the most suitable speed and it keeps a high efficiency over a wide load range. In addition, the analysis of the techno-economic parameters for such a system provides an important dataset for micro-PHES feasibility breakdown.PaTs are a legitimate cost-effective option in micro hydropower but an universal performance prediction does not exist. Their hydraulic efficiency can possibly shift from the higher efficiency of traditional hydraulic turbines. Nowadays, these reasons restrict PaTs exploitation. In this thesis, a multivariate regression method is applied to the CFD results to build a surrogate model of the PaT hydraulic characteristics as a function of the cutwater geometrical modifications. Based on this model, an optimization problem is solved to identify the most advantageous geometrical assetof the PaT cutwater to maximize the hydraulic efficiency. The presented methodology and design optimization of the cutwater in PaTs, which are extremely suited to our current energy generation needs, provides a unique and much-sought guide to its performance, improvements, and adaptation to hydropower. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Hydraulic design of a hydrodynamic machine is designed to achieve a high value of energy transformation efficiency. Pumps and turbines have some different typical features in hydraulic design. With the aid of computational fluid dynamics, adjustments of the hydraulic parts of a standard centrifugal pump are assessed with the aim to increase hydraulic efficiency of the pump running as turbine. The impeller, volute casing and added draft tube are discussed.

This master‘s thesis deals with a centrifugal pump running in reverse (turbine) mode, often called “pump-as-turbine”. The introduction lists basic principles and information about the direct (pump) and reverse modes. Several methodologies for predicting reverse operating point and efficiency evolution are used and compared with simulation results. Using CFD simulations, results obtained with simplified (excluding impeller side wall gaps) and complete geometry (including impeller side wall gaps) are assessed. Furthermore, the results of impeller trimming are evaluated with an aim to find the maximum power and efficiency. Impeller side wall gaps effect is analyzed in terms of friction torque and power loss.