Parameter influence assessment of circumferential groove casing treatments in an industrial centrifugal compressor for enhanced operational flexibility

With the increased integration of renewable energies, an expanded and flexible operating range for industrial centrifugal compressors is becoming increasingly important. The operating range of compressors is delimited by the choke limit at high mass flow rates and by the surge limit at low mass flow rates. One option for expanding the operating range without significantly compromising efficiency is the use of casing treatments (CTs). CTs have often been studied in axial compressors, where they are occasionally implemented. Applications and studies are not as widespread in centrifugal compressors. Among these, applications and studies mainly focus on ported shrouds in turbochargers. This thesis aims to evaluate the effect of the main geometric parameters defining circumferential grooves on the performances and stability of a typical industrial centrifugal compressor. The influence of the design parameters on performance parameters and indicators for stable behavior is examined, with operating points at high and low speed being investigated. To achieve these objectives, several geometries are parameterized and generated following a DOE approach (specifically, a central composite design) in order to obtain a statistically consistent dataset. The geometries are simulated with CFD RANS equations, and the obtained results are employed to construct regression models used to identify linear, quadratic and interaction terms. This study shows that circumferential grooves can extend the operating range of the industrial centrifugal compressor under investigation in the high speed range. At low speeds, no extensions to the operating range are achieved. The influence of all CTs investigated on the performance data is small but measurable, and they tend to cause a reduction in efficiency in most cases. Different behaviors can be observed in the analyzed indicators depending on the operating point and geometry. It can be seen that the axial position and width of the grooves are particularly relevant design parameters for effective CTs. The findings of this study show that the evaluation of the effectiveness of CTs depends heavily on the observed operating point and the geometries of the grooves and serve as a basis for further research and future optimization.