The influence of inlet flow distortion on the performance of a centrifugal compressor and the development of an improved inlet using numerical simulations

The performance of centrifugal compressors can be seriously affected by inlet flow distortions due to the unsatisfactory nature of the inlet configuration and the resulting inlet flow structure.; Experimental tests have been carried out for the comparison of a centrifugal compressor stage performance with two different inlet configurations: one of which is straight pipe with constant cross-sectional area and the other is a 90-degree curved pipe with nozzle shape. The comparative test results indicated significant compressor stage performance difference between the two different inlet configurations, and the details are discussed to understand the performance behavior of the compressor exposed to the distorted flow from the bend inlet configuration.; The experimental investigation motivated the need of a new inlet design as well as a clear picture of the detailed flow field in the existing inlet design using numerical simulations. Two design approaches are reported in this research work: one of which is the location of vanes and the other is the length of curvature radius. For more effective way of design, a generalized formula is developed for the optimum position and the number of vanes in such a way that each divided flow passage with vanes shares the same pressure gradient in radial direction. Numerical simulation results are presented and discussed in terms of mass averaged parameters and flow structures, based on the comparison of flow properties at the pipe exit cross-sectional area of each design. Finally, new designs of different inlet systems are proposed to reduce the secondary flow and provide enhanced flow for a compressor.; Steady-state compressor stage simulation including an impeller and a diffuser with three different inlets attached for each case has been carried out to investigate the influence of three different inlet systems including the proposed inlet model on the compressor performance. Since the flow from the bend inlet is not axisymmetric for the circumferential and radial distortion, the diffuser and the impeller are modeled with fully 360 degree passages, which makes it possible to detect the distortion influence on all of the impeller and the diffuser passages as well as the interaction between the impeller and the diffuser causing circumferentially non-uniform properties among the passages. The stage performance and the diffuser performance are compared quantitatively for each inlet system.; Additional experimental tests has been carried out for the comparison of three different diffusers with the combination of the straight and the bend inlet systems. The influences of the inlet distortion on the compressor stage performance for each diffuser are presented in terms of the stage efficiency, the head coefficient, the work coefficient, the static and the total pressure ratio. The contributions of the different diffusers to the stage performance for each inlet system are discussed in detail.