Sensitivity Study on the Impact of Surface Roughness Due to Milling on the Efficiency of Shrouded Centrifugal Compressor Impellers

To discuss the impact of the surface roughness on the efficiency of shrouded centrifugal compressor impellers, this paper presents a theoretical examination of different parameters influencing their aerodynamic behavior. The work is based on the available literature about the influence of surface roughness on the aerodynamics of fluids. An algorithm was derived from different theoretical approaches, which allows computation of the prospective efficiency deficit of radial impellers, dependent on the specific technical roughness. With the help of a numerical code, the impact of several parameters on the efficiency of a shrouded radial impeller due to surface roughness was evaluated. Additional to the expected efficiency drop at the design point of the impeller, the computations were extended for a wide range of operating conditions covering partial loading as well as overloading conditions. All results are discussed in comparison to a hydraulically smooth impeller surface. Thus, only additional losses due to surface roughness are focused on.