Prediction of surface roughness effects on centrifugal compressor performance

Abstract

The present paper deals with the effect of the surface roughness on the performance of centrifugal compressors and the applicability of the Computational Fluid Dynamics (CFD) for the purpose of the quantitatively accurate prediction of the performance deterioration due to the surface roughness. Commercial CFD solver FLUENT was applied in the current research. High Reynolds number turbulence model was used with the wall function corrections to the rough walls. In the initial phase, CFD analyses were conducted on an axial compressor and an axial turbine cascades, those geometrical and experimental data on the effect of the surface roughness are publicly available. The comparison of the CFD results with the experimental data showed reasonable agreement in view of the increase in the cascade loss coefficient at the cascade design conditions, although less satisfactory agreements were obtained at some off-design conditions. In the next step, a series of performance testing was conducted on the centrifugal compressor stages, whose wetted surfaces are intentionally roughened by sand-blasting surface treatment. Corresponding CFD analyses were conducted. In these analyses the intensity and extent of the surface roughness were appropriately modeled based on the observations and measurements of the surface texture. Efficiency decrements were compared and good agreements were confirmed between them. In this case, good agreements were obtained not only for the design conditions but also for the wide range of the off-design conditions. Based on the above analyses and comparisons with experimental data, following conclusions were obtained. Reasonable quantitative agreements between experimental data and CFD analyses were obtained on axial compressor and turbine cascades and centrifugal compressor stages. CFD analyses with wall roughness can be used to estimate the detrimental effect of the surface roughness. Copyright © 2008 by ASME.