An academic test rig for industrial centrifugal compressor stages: A design approach

Due to the huge amount of power connected to centrifugal compressors' applications, even small rangeability increases of the stages would provide significant energy and money savings. In particular, industrial manufacturers pay lot of interest in better understanding the instabilities that in many cases define the minimum flow limit of their stages, but they are often hampered in the research by the short time-To-market. On the other hand, academia has historically found difficulties in approaching the problem due to the lack of dedicated experimental facilities. In this study, the concept design of a new research test rig is presented. The rig will be able to test impellers in field-like conditions (original mass flow and peripheral Mach numbers up to 0.7), operating in open-loop configuration with ambient inlet conditions. In view of systematic test campaigns, a modular design will allow to easily replace any component of the asset and even to modify the flowpath after the impeller, so that the influence of each component can be estimated. As a research academic facility, the rig is characterized by some new design solutions, oriented to minimize the mechanical complexity, the energy consumption, the overall dimensions, and, finally, the cost. Moreover, it will be equipped with advanced experimental measurement instrumentation, e.g. a PIV system or fast response aerodynamic pressure probes. The paper illustrates the conceptual design of the rig, including the selection of the best architecture and layout, the drivetrain assessment and the rotordynamic verification. Computational fluid-dynamic analyses are also presented, aimed at verifying the flow uniformity in the discharge sections and the thermal stability of the system during the tests.