Use of CFD Analyses to Predict Disk Friction Loss of Centrifugal Compressor Impellers

Abstract

To improve the total efficiency of centrifugal compressors, it is necessary to reduce disk friction loss, which is expressed as the power loss. In this study, to reduce the disk friction loss due to the effect of axial clearance and surface roughness is analyzed and methods to reduce disk friction loss are proposed. The rotating reference frame technique using a commercial CFD tool (FLUENT) is used for steady-state analysis of the centrifugal compressor. Numerical results of the CFD analysis are compared with theoretical results using established experimental empirical equations. The disk friction loss of the impeller is decreased in line with increments in axial clearance until the axial clearance between the impeller disk and the casing is smaller than the boundary layer thickness. In addition, the disk friction loss of the impeller is increased in line with the increments in surface roughness in a similar pattern as that of existing experimental empirical formulas. The disk friction loss of the impeller is more affected by the surface roughness than the change of the axial clearance. To minimize disk friction loss on the centrifugal compressor impeller, the axial clearance and the theoretical boundary layer thickness should be designed to be the same. The design of the impeller requires careful consideration in order to optimize axial clearance and minimize surface roughness.

Flow Inside the Sidewall Gaps of Hydraulic Machines: A Review

“…In cases of extremely narrow gaps where the clearance is smaller than the thickness of the boundary layers, the value of c m is very high, decreasing to its theoretical minimum, while increasing the axial gap. It is according to [93], who reached the ratio s/r = 0.032, which corresponds to the theoretical boundary layer thickness. The authors explain the enlargement of the disk friction losses by increased recirculation area caused by increments in axial clearance.…”

“…Gülich [8] states, that the tolerance of estimation of disk friction losses according to previously derived empirical equations is about ±25%. For that reason, nowadays, numerous authors use CFD for the determination of disk friction rather than an empirical approach, see e.g., [90,93,99,100].…”

Flow inside impeller sidewall gaps and disk friction of radial centrifugal pump

“…1 right. Effect of Reynolds number, surface roughness and axial gap in connection with realistic shapes used in turbomachinery were studied, e. g. in [7][8][9]. Beside the mentioned parameters, disk friction is influenced by the shape of the stator and sidewall gaps, leakage flow, partload recirculation and exchange of momentum, which can be altogether hardly expressed by a single formula [1].…”

“…Considering the main pump fluid regions, the methodology of such analyses is described in many studies, e.g. [9][10][11][12][13].…”

“…SST k-ω and k-ε Realizable are the most common and in many cases justified turbulence models. The most of the CFD studies neglects the influence of sidewall gaps on the global flow and the regions of front and back side disk gaps are not involved into the simulation at all, as can be seen in [9][10][11][12][13]. The studies, where it is included [14, 15], do not show any special approach in order to resolve the flow in those regions.…”