Analisi e criteri progettuali per compressori centrifughi dotati di Ported Shroud

In road applications, a centrifugal compressor is often required to work in conditions other than optimal because of the various operating conditions it is subjected to. In addition to its main performance (efficiency and pressure ratio), the centrifugal compressor must have a wide stable operating range. Among the different techniques used to extend the operating range of the compressor is the ported shroud that will be the subject of our study. Ported shroud is a technique frequently adopted in the design of compressors for automotive turbochargers. Its operating principle consists, during low-flow operation, in recirculating the swirling structures from the casing (shroud) of the impeller towards the entrance of the stage in order to release a fraction of the main flow by eliminating instability in the region of the impeller tip. The challenge for designers is to create a recirculation cavity configuration that widens the compressor’s operating range, minimizing the impact on efficiency. However, the early stages of design of the recirculation cavity rely mostly on results from expensive CFD executions, and therefore require excessive computational resources. The aim of this Phd thesis is the development of an analytical model that allows to predict the effect of a given cavity on a known centrifugal compressor without the use of other calculations made with the CFD. The results obtained by the model were compared with the CFD data of a centrifugal compressor equipped with ported shroud. It has been shown that the model allows to predict the effect of the cavity to be applied on a known centrifugal compressor with an acceptable margin of error in the points close to the stall. In addition, having two cavities available, it was possible to choose the cavity that has the greatest advantage in extending the field of the compressor thanks to the analytical model developed. This conclusion was confirmed by comparison of the field of operation.