Improving Structural Integrity of a Centrifugal Compressor Impeller by Blading Optimization

Three-dimensional blading features of impellers like sweep and lean improve the aerodynamic performance of centrifugal compressors, especially in terms of pressure ratio, stall margin and efficiency. But, these blade geometrical features often impose challenges on mechanical design and structural integrity of the impeller. Modern small gas turbine engines demand high-work input impellers rotating at very high speeds, making the structural design even more difficult. The present study deals with improving the structural integrity of a centrifugal impeller of a compressor stage designed for 42,000 rpm and power input of 1200 kW. The baseline design of the impeller, arrived using an advanced three-dimensional design software, met the aerodynamic performance requirements but failed to satisfy structurally. Higher backward lean present in the blade was found to be contributing to severe bending stresses and deformation. Hence, three different impellers, with modified thickness, lean angle and wrap angle distributions, were designed. These designs were subjected to 3D CFD and FEM analysis. Structural analysis was carried out to study stresses and deformations for all configurations, followed by pre-stressed modal analysis to predict their natural frequencies and corresponding mode shapes. The design with modified wrap angle distribution not only met the aerodynamic requirements but also satisfied structural requirements. This paper elaborates the design evolution of the centrifugal impeller from the baseline design to a more structurally stable one