*Numerical and experimental study of the flow in side-channel blowers*

Regenerative machines are known for their ability to achieve high heads at low flow rates while exhibiting stable performance curves. Despite being the subject of scientific inquiry since the 1940s, the precise mechanism responsible for generating high pressure in regenerative flow compressors remains incompletely understood. In this study, we conducted experimental and numerical analyses on a series of 13 regenerative flow compressors in collaboration with FPZ S.P.A company. Our objective was to investigate the flow characteristics within these machines and identify geometric parameters that significantly impact efficiency. The first phase of our study focused on the experimental and numerical analysis of the E08 family of regenerative flow compressors across four different rotational speeds (1000, 2000, 2990, and 3500 rpm). Our findings revealed that increasing pressure rise led to a drop in efficiency, with circulatory flow exerting a stronger influence on losses. Additionally, our results indicated that unsteady simulations tended to overpredict losses attributed to increased circulatory flow, whereas steady simulations aligned more closely with experimental data, consistent with observations by other researchers. In the subsequent phase of our study, we simulated 12 different geometries to evaluate their impact on compressor efficiency. To standardize comparisons, we maintained a rotational speed of 2900 rpm and an outer radius of 0.430 mm across all geometries, while varying the depths of the rotor and stator, as well as the inner radius of the compressor. Our analysis revealed that among geometries with constant rotor and stator depths, compressors with smaller inner radii exhibited higher pressure rise but lower efficiency, whereas those with larger inner radii demonstrated higher efficiency but lower pressure rise. Furthermore, our simulations indicated that increasing the size of the casing resulted in a notable jump in pressure rise at low flow rates, up to a certain threshold beyond which pressure began to decline. Additionally, larger casings exhibited decreased efficiency at high-pressure working points due to flow separation, whereas smaller casings demonstrated improved efficiency. Our findings suggest a limitation on increasing casing depth, beyond which further increments result in decreased pressure ratio. Conversely, an increase in rotor depth led to improved efficiency and higher pressure rise, while maintaining constant outer and inner radii. In conclusion, our study provides valuable insights into the factors influencing the efficiency of regenerative flow compressors, shedding light on the interplay between geometric parameters and performance characteristics.