• Energy Research
• EU close

Abstract This paper explores two different blisk dynamic models for resonant vibration prediction of a rotating blisk test piece, i.e. the Model-BDTID and GMM. The former represents a mistuned blisk model with blade mistuning pattern experimentally retrieved by a recently proposed blade mistuning identification method based on blade detuning tests (BDTID). It falls into the scope of the frequency-mistuning modeling approach. The latter refers to a geometrically mistuned model constructed upon high-precision blisk geometry data by leveraging the advanced optical geometry measurement technology. A specifically developed ‘Sector Mode Assembling Reduction Technique’ is exploited for efficient dynamic analyses of the large-sized GMM. Forced response tests are performed in a spinning rig under well-controlled laboratory condition. The Blade Tip-Timing technique is employed to give all-blade vibration measurements of the rotating blisk. Correlation results between the forced response predictions to BTT measurements demonstrate that both the Model-BDTID constructed upon the identified blade mistuning of the blisk at rest and the GMM, can predict the resonant vibration of the rotating blisk with satisfactory accuracy.

This paper presents a novel blade mistuning identification method based on blade detuning tests. Blade detuning tests consist of blade-by-blade impact testing in a blisk with detuning masses purposefully attached on all the blades except the one currently under test. Due to the quite simple test setup and implementation, the detuning tests enable to estimate the blade frequency mistuning pattern of the blisk with low experimental effort. However, it was proved that non-negligible residual inter-blade coupling is responsible for an inaccurate identification of the truly ‘blade-alone’ mistuning pattern from the blade detuning test results. Therefore, a novel mistuning identification method is herein proposed in order to improve the accuracy of the estimated mistuning pattern. This method fully exploits the blade detuning test results and includes the residual inter-blade coupling due to the mass detuning mechanism. The quantification and the introduction of the residual inter-blade coupling into the identification procedure leads to the determination of a more accurate ‘blade-alone’ frequency mistuning pattern. This novel mistuning identification method is firstly validated in a numerical test case and then applied to a real blisk test piece.

Blade mistuning in blisks arises primarily from the scatters of blade geometry profiles caused by manufacturing tolerance, in-service wear, blade repairs, etc. There is a recent trend to capture the blade-to-blade geometry variances through precise geometry measurements by a 3D optical scanning system in order to obtain an improved blade geometric mistuning evaluation capability. However, this usually leads to prohibitive computational costs due to the large-scale, high-fidelity industrial blisk finite element models. This paper develops an original model reduction approach, Sector Mode Assembling Reduction Technique (SMART), specifically for the high-fidelity blisk model fully mistuned by blade geometric variances, with either topologically compatible or incompatible blade meshes. The basic idea of SMART is to construct the sector-level reduction mode basis by strategically assembling the truncated cyclic modes independently computed for each “isolated” sector with assumed cyclic symmetry at the sector interfaces. Benefiting from the block structure of the SMART mode basis, the reduced-order models are derived by a series of sector-level projections with a relatively low memory requirement and computational cost. Another hidden benefit is that the SMART approach enables efficient structural modification predictions of the global blisk modes because only the modes of the sectors undergoing blade modification need to be re-evaluated and replaced in the SMART mode basis. The SMART approach is applied into a high-fidelity “as-measured model” of a blended blisk, constructed upon the geometry measurement by the state-of-the-art 3D optical scanning technology. It is fully demonstrated that the reduced-order model derived by SMART, featured by a minimal size, is able to reproduce the dynamics of the full-order as-measured blisk model with high accuracy.