Modeling of Partially Shrouded Impellers' Effect on Operating Efficiency and Flow Range of Centrifugal Compressor

摘要

The centrifugal impeller is one of the most critical aerodynamic parts of centrifugal compressors. The previous experimental investigation demonstrated that the fully shrouded impeller is better in terms of efficiency whereas the unshrouded configuration is typical for wide flow range. To compromise between the high efficiency and wide flow range requirements, partially shrouded impellers have been developed, attaining reductions in the efficiency loss due to tip clearance while keeping a sufficient surge margin. However, the selection of the optimum shrouded percentage is influenced by several variables including stage efficiency, pressure losses coefficient, manufacturing cost, required power cost, resonance frequency, and stable operating range influenced. Hence, an optimization is required to compromise between these parameters to ensure better performance. This paper will introduce a new empirical approach to model the effect of shrouded percentage on these parameters which will help to specify the optimum configuration at an early preliminary design stage based on the sort of the application and according to the expected variation in the operating conditions. This model has been examined at high and very low flow coefficients and Mach numbers operating conditions, and the obtained parameters are compared with the computational fluid dynamics (CFD) simulation results and the recorded measured data in order to emphasize the validity of the new method. The conducted comparison revealed a good agreement between the obtained parameters by the new model and those derived numerically and experimentally with a maximum deviation of around +/- 3.0%. One of the main features of the developed method over the CFD approach is the fact that it does not require deep knowledge about the stage geometrical features; thus, it can be used in the early preliminary design process. Moreover, the included optimization emphasizes the need for a compromise decision in order to select the impeller configuration.