Practical Application of Basic Fluid Mechanic Relations to Estimate the Impact of Surface Roughness Due to Milling on the Aerodynamics of Shrouded Centrifugal Compressor Impellers

摘要

To discuss the impact of surface roughness due to milling of shrouded centrifugal compressor impellers out of one piece of raw material on the efficiency, in this paper a theoretical examination of several parameters influencing the aerodynamic behavior is presented. The work is based on the available literature upon the influence of surface roughness on the aerodynamics of fluids. Outgoing from a theoretical approach which is established on the basic fluid mechanic relations an algorithm was created which allows to compute the prospective efficiency deficit of radial impellers in dependence on the specific technical roughness. With the help of the 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 part load as well as overload conditions. All results are discussed in comparison to a hydraulically smooth surface of the impellers. Thus only additional losses due to surface roughness are focused on.