spool compressor, geometry optimization, theoretical analysis
A theoretical study of the influence of scaling is presented for the rotating spool compressor. This study uses the previously developed comprehensive compressor model for the rotating spool compressor developed by Bradshaw and Groll (2013). Using this model a study of the influence of the compressor volumetric displacement is performed. This study relies on a set of scaling rules to determine the size of the compressor features as the compressor displacement changes. The study finds that as the volumetric displacement increases, the volumetric efficiency asymptotically increases. It is also found that there is an optimum in overall isentropic efficiency as the volumetric displacement increases which suggests a trade-off between sealing and port restrictions. The compressor aspect ratio (axial length to bore diameter) is varied between roughly 0.2 and 3.5 at eccentricity ratios (rotor diameter to bore diameter) of 0.825, 0.85, 0.893, and 0.92. It is found that for a given eccentricity ratio, there exists an optimum aspect ratio that maximizes sealing. Additionally, the eccentricity ratio shows a high level of sensitivity to the overall performance of the compressor. As the eccentricity ratio decreases, the overall isentropic efficiency of the compressor increases until an eccentricity ratio of 0.85. Below an eccentricity ratio of 0.85 the overall isentropic efficiency does not increase despite an increase in volumetric efficiency.