STATISTICAL IMPACT OF MANUFACTURING TOLERANCES ON AXIAL GAPS BETWEEN VANE SEGMENTS AND THE ROTOR OF AXIAL FLOW TURBO-COMPRESSORS

摘要

Geometrical deviations arising from the manufacturing process significantly influence the axial gaps between rotating and nonrotating parts. To optimize axial gaps and thus reduce the overall length and weight of the compressor, it is essential to take the statistical nature of these deviations into account. The focus of this paper is to identify complex three-dimensional effects caused by geometrical uncertainties. The results can be then used to define an appropriate level of detail for the simulation model in order to accurately predict the probability distribution of axial gaps. In the simulation model the parts are assembled according to defined mechanical constraints and the paper presents mathematical models regarding this. A simplified 2D model of a sectional view and a detailed 3D model are implemented and investigated. A 2D tolerance analysis shows that a statistical gap tolerance can be defined based on geometrical parameters. It must be assumed that a certain percentage of all gap values will fall below the lower specification limit for this tolerance interval. A detailed 3D analysis, however, results in a change in the probability distribution of the gap values compared to the simplified 2D analysis. In addition to the standard deviation, the mean value of the gap is reduced significantly. Therefore, a simplified 2D approach may yield invalid results. What this effect is will depend on the configuration. One influencing factor is the number of vane segments in the compressor stage. A sensitivity analysis is presented which identifies and quantifies the impact of such important design parameters.