Influence of Reynolds Number on the Performance of Process Centrifugal Compressors

Abstract

Over the past 60 years, effects of changes in Reynolds number on performance of centrifugal compressors have been widely investigated. However most of cases deal with those compressors with small or medium flow coefficients. Studies on the influence of Reynolds number on centrifugal compressors with large flow coefficients and high machine Mach number are rarely seen in the literature. This paper deals with two types of centrifugal compressors. One type of compressor (Model 1) has a relatively large capacity with high machine Mach number. The flow coefficient and machine Mach number are 0.16 and 1.05 respectively at the design condition. Those design parameters for the other type of compressor (Model 2) are 0.11 and 0.7 respectively. Both experimental and numerical results show that with increase in Re, aerodynamic performance of centrifugal compressors is improved. However, to what extent that improvement is gained depends on properties of the baseline compressor. When Reynolds number of Model 1 becomes about 5 times large due to increase in the inlet pressure, its polytropic efficiency is only improved 0.7% at the design point in experiment. Flow field inside the impeller is similar to its prototype. For Model 2, when Reynolds number becomes 1.78 times large due to scaling up, the polytropic efficiency of the enlarged one is improved about 2% at the design point. These results demonstrate that for a compressor with large flow coefficient and high machine Mach number, i.e. originally high Reynolds number, the influence of Reynolds number on its performance is limited. In addition to experiment and CFD, two empirical formulas are applied to work out performance correction due to a change in Reynolds number for Model 1 and Model 2. Although CFD results are more accurate than the empirical results, empirical formula is still useful to get relatively reliable performance correction.