PhD Thesis - Stiaccini

Modellazione ibrida tempo-frequenza per analisi di compressori alternativi e rispettivi impianti. L'approccio consente di valutare l'interazione tra la macchina e l'impianto. Al fine di modellare in dettaglio le cavità complesse della macchina, è stata definita ed applicata una procedura di caratterizzazione basata su risultati di simulazioni realizzate con FEM acustico. La metodologia di modellazione è stata applicata ad un compressore per cicli frigoriferi a CO2 e verificata attraverso il confronto con dati sperimentali. An accurate and effective numerical modelling of the reciprocating compressors in the preliminary phase of design can assure reliability in the operating conditions and avoid failures. In most cases, the geometric complexity of some elements interacting with the compressor, such as plena and mufflers, makes both the fluid-dynamic 1D and acoustic lumped parameters modelling of the system unable to assure the required detail level necessary for the design process. For this reason, an acoustic numerical characterization is the most suitable way for the analysis of the response of geometrically complex elements. In order to analyze the thermodynamic and acoustic performance of a compressor for refrigerating application, a hybrid numerical model is developed that allows to carry out simultaneously the time-domain analysis of the compressor thermodynamic cycle and the frequency-domain acoustic analysis of the pipelines system. An acoustic characterization method based on acoustic FEM simulation results was also defined to model in detail the compressor cavities with complex geometries (i.e. compressor plena). The results of the compressor hybrid model with both acoustic FEM characterization and acoustic lumped elements were compared with experimental measurements. Moreover, a comparison between the developed hybrid model and the stand-alone compressor model with constant pressure boundary conditions was carried out. The advantages in using the acoustic FEM characterization of the complex geometry elements were highlighted.