A combined experimental and numerical approach to support the development of next generation centrifugal compressors for hydrogen applications

The PhD research presents a tailored approach to support the industry in the development of new centrifugal compressor design for Hydrogen compression. The definition of the real performance of a compressor and also the analysis of the source of losses are particularly important, especially during the early validation phase. To this aim, a dedicated test rig was developed and validated inside the University of Florence to ensure quick and reliable results and guide the development of the final design of a single stage of a compressor. The results of an extensive testing campaign on different versions of the same centrifugal impeller have led to the validation of a geometry suitable for the compression of Hydrogen. At the same time, it highlights several critical issues related to leakage through labyrinth seals and through the blade of the vaned diffuser. Thanks to the support of the industrial partner Baker Hughes, it was therefore possible to experimentally validate the simulation models and to analyse in detail the different sources of losses. An in-depth analysis of the effects of the variation of the gap between the vaned diffuser blades and of the leakage losses through the labyrinth seal at the impeller eye was conducted at the University of Florence test rig, paying particular attention to the variation in performance and operating range of the compressor stage. Finally, the development of an innovative design for the labyrinth seal capable of reducing the leakage and maintaining the same clearance is presented. The experimental results of the preliminary testing campaign on the new labyrinth seal were presented and discussed leaving space for further investigations. In the last phase of the research, to support the introduction of innovative technology at both industrial and academic levels, the testing of a discharge volute made in plastic material and rapid prototyping technology is presented. This approach can reduce the time and costs of implementation, very crucial during the research and development phase of the product, allowing the test of different features difficult to replicate with other construction technologies and keeping the result of the experiment.