<p>The flow exiting the guide vanes in Variable Geometry Turbines exhibits a wide range of unsteady flow features.&nbsp; The nature of the flow non-uniformity varies as the nozzle vanes rotate through different positions during operation, as do the magnitudes and frequencies of the resulting pressure fluctuations experienced by the downstream turbine blades.&nbsp; Automotive turbocharger turbines typically pass through a number of blade natural frequencies over their operating cycle, and there are therefore a number of potential conditions where these unsteady aerodynamic loads will produce resonant blade vibration.&nbsp; The resulting vibration displacements and stress amplitudes can create a significant risk of High Cycle Fatigue (HCF), and the task of the engineer is to design to avoid the most harmful resonance conditions, and otherwise minimise both the alternating and centrifugal stresses in the blades.&nbsp; The focus of this work is on the development of a practical design approach to improve the structural characteristics of a radial turbine blade with respect to HCF.&nbsp; This paper describes the structural optimization of a high speed, radial turbine wheel in a VGT system, subjected to the wise range of aerodynamic loads experienced during the full operating cycle.&nbsp; Unsteady Computational Fluid Dynamics (CFD) simulations are performed to determine the time-accurate pressure loads on the blades, and the results are used as input to forced response analysis to determine the peak alternating stress amplitudes.&nbsp; The blade geometry has been parametrically varied to investigate the influence of section thickness changes and hub fillet details on structural response, and optimised designs identified through the use of a Turbine Goodman Diagram.</p>

Hcf Optimization of a High Speed Variable Geometry Turbine

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

Turbo Expo 2021

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