Accurate Strain Gauge Limits Through Geometry Mistuning Modeling

摘要

Safe engine operation is ensured by setting safety limits on rotor airfoil-mounted strain gauges that monitor the dynamic response of the component. Traditionally, strain gauge limits are generated using geometry obtained from an "as-designed" nominal model, in which finite element analysis is used to compute the static and modal stresses. Predicted modal stresses of the cyclic analysis are used to optimize strain gauge locations to ensure modal observational coverage, modal identification, and maximum vibrational stress for each mode. Strain gauge limits are then produced for these optimal strain gauge locations on the tuned finite element model. This described nominal geometry based process is subject to errors associated with airfoil mode-shape variations caused by manufacturing deviations. This paper develops a new process based on as-manufactured geometry measurements from a high-fidelity optical geometry collection system that obtains more accurate strain gauge limits. It will be shown that, because of the variability of blade-to-blade geometry, strain gauge limits can vary significantly between blades. This will be demonstrated by analyzing a mistuned integrally bladed rotor on a sector-by-sector basis. The approach used in this paper has the capability to more accurately place gauges on responsive blades to ensure safe engine operation during testing.