Periodic Reporting for period 3 - ARIAS (Advanced Research Into Aeromechanical Solutions)
Reporting period: 2021-09-01 to 2023-02-28
The aim of the ARIAS project is to improve the design methods employed by aircraft engine manufacturers to predict aeromechanical vibrations which occur due to the interaction of the component vibration with the airflow through the machine. A pursuit of higher efficiency, compactness and low-weight engine designs often leads to increased susceptibility to harmful aerodynamically induced vibrations, thereby putting engine integrity into direct conflict with greening aspects. The current industry standard methods are limited in their ability to predict correctly aeromechanical vibrations and if harmful vibrations are discovered during the testing phase, this will lead to a redesign, which will add significant cost and time to the overall product development process. In practice, the limitations of current methods generally lead to over-conservative designs, where unwanted aeromechanical behaviour is avoided at the expense of cost, weight and complexity in the components. In the most extreme cases, aeromechanical vibrations can compromise the structural integrity of engine components, which can have significant safety and reliability consequences. Having access to more reliable design methods will enable optimisation of aeromechanically acceptable component designs, facilitating the production of more efficient, reliable and quieter engines in line with the ambitions of ACARE2020 and Flightpath 2050.
The overall objective of the ARIAS project is to improve the flutter and forced response predictions of jet engines to secure better designs leading to safer, more cost-effective, lighter, and more efficient engines with reduced emissions. This objective is achieved by:
• Establishing the influence of various structural and fluid characteristics on both propensity to flutter and forced response of blades and labyrinth seals by acquiring high quality unique experimental data through extensive experimental campaigns, and;
• Using the enhanced understanding to aid the development of a range of preliminary design guidelines and improved, validated analysis tools of varying sophistication for each stage of the design process.
The overall objective of the ARIAS project is to improve the flutter and forced response predictions of jet engines to secure better designs leading to safer, more cost-effective, lighter, and more efficient engines with reduced emissions. This objective is achieved by:
• Establishing the influence of various structural and fluid characteristics on both propensity to flutter and forced response of blades and labyrinth seals by acquiring high quality unique experimental data through extensive experimental campaigns, and;
• Using the enhanced understanding to aid the development of a range of preliminary design guidelines and improved, validated analysis tools of varying sophistication for each stage of the design process.
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
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
The experimental data and methods developed within the ARIAS project will have direct application in both understanding and interpreting the behaviour and measurement data produced by the demonstrator and development engines and optimising the design of the subsequent production families of engines. It will create an accelerated impact on vibration-related redesigns of current turbofan engines and the design of new more efficient, reliable and robust engines. The generated knowledge will also improve the quality of the education of future engineers in turbomachinery aeromechanics.