To achieve the project objectives significant efforts were put into conducting extensive experiments at seven different locations across Europe. In parallel with the experiments, comprehensive simulation campaigns were carried out by multiple partners and comparisons with the testing results were possible. The technical work was organized in four work packages:
WP1 Flutter and forced response in compressors
With a focus on compressor forced response and flutter studies, WP1 has fulfilled the objectives that were set at the commencement of the project. The aim was to collect high-quality experimental data that is used for validation and method development. In the process, innovative measurement techniques were adopted. High-quality experimental data is made available to all partners from four test campaigns i.e. transonic compressor tests at TUDA, compressor tests at USTUTT, transonic cascade tests at KTH and rotating vacuum rig tests at ECL. These data sets are of great value for project partners in validating and improving present analysis methods for compressor forced response and flutter. Comparisons against the experimental data indicate that aero-damping predictions by various partners have less scatter in reference to experimental data, compared to what was observed in the previous EU project FUTURE. However, a rather large spread in the forced response vibration amplitude predictions is present among the partners and the results are not entirely in line with what was measured, indicating that there is still a need for further improvement of these methods. Vibration mitigation techniques like split ring dampers and intentional mistuning were successfully assessed using innovative testing methods in the vacuum rotating rig.
WP2 Non-linear aeroelastic interactions in turbines
The WP2 involved two extensive experimental campaigns, both in Avio’s STARGATE spin-pit rig and CTA’s cold-flow test rig, which allowed a detailed characterization of flutter and forced response phenomena in a representative turbine stage. The campaigns also included testing considering two advanced technologies for the suppression of vibrations in turbines: under-platform dampers and intentional mistuning.
The WP also included an ambitious simulation campaign, where the capabilities of a number of analysis tools and methodologies for reproducing the experimental results were demonstrated. In particular, advanced methods that were able to represent accurately the interaction between flutter and forced response were developed. As a result, the understanding of the physics behind flutter and forced response, and their interaction, was greatly expanded. The experimental campaign also allowed the definition of a detailed set of high-quality validation cases for simulation tools for turbine aeroelasticity. The maturity of the technologies of under-platform dampers and intentional mistuning also increased.
WP3 Flutter in labyrinth seals
The WP3 successfully delivered against its objectives to provide high-quality experimental data and advance methods associated with the prediction of labyrinth seal flutter. A unique static seal flutter facility was built at ICL, where extensive experiments were undertaken on two seal designs across a range of pressure ratios, fin tip gaps and flow directions with both free and forced vibration being explored.
Results were used to evaluate and validate a range of prediction methods from simple 1D approaches to high-fidelity 3D CFD. Synthesis of the experimental data with these methods highlighted where simple prediction tools may and may not be applicable as well as validating instability trends and aerodynamic damping values predicted by more complex approaches. This synthesis also shows where further research would be beneficial, for example where instability trends are accurately predicted but absolute values of aerodynamic damping and threshold pressure ratios are not.
WP4 Future enabling technologies
The following tasks were successfully accomplished:
-application of weak- and strong coupling simulation approach for forced response prediction in the TUDA rig
- development of an innovative method for nonlinear forced response analysis of the LPT rotor, capable of assessing configurations with under platform dampers, mistuned set of blades, and overlapping synchronous and non-synchronous vibrations sources
- development of semi-analytical approaches for seal flutter prediction & demonstration of accelerated computing techniques
- advanced blade monitoring through innovative tip-timing algorithm techniques and unsteady pressure measurements for blade vibration detection
- demonstration of vibration control with piezo-electric dampers
