Design, Optimization and Evaluation of a Transonic Aeroelastic Rig
Time: Fri 2021-05-28 09.00
Subject area: Energy Technology
Doctoral student: Simeng Tian , Energiteknik, HPT
Opponent: Professor Dieter Peitsch, Technische Universität Berlin
Supervisor: Andrew R. Martin, Kraft- och värmeteknologi, Energiteknik; Dr. Mauricio Gutierrez Salas, Energiteknik
The compressor is one of the most essential components of a modern turbomachinery engine. This component is exposed to vibrations that without proper design can damage structural integrity and lead to failure. Due to the unsteady flow that is inherent in compressors, characterized by transonic flow and high aerodynamic loading, the blades are prone to high cycle fatigue (HCF). Forced response assessments are needed to quantify the vibrational amplitude under resonance and determine the stresses for possible HCF problems. Resonance occurs when the blade’s natural frequency is excited by an external force. At specific frequencies, the resonant effect will significantly affect the performance of the compressor blade. In the forced response prediction, one of the crucial processes is the aerodynamic damping calculation. There are various models and numerical methods that are used for the damping prediction. However, there is a lack of experimental data for the numerical validation at high frequencies, which limits the research. A new aeroelastic rig is necessary to investigate the unsteady pressures when determining the aerodynamic damping in a transonic compressor.
The design of the new aeroelastic rig was developed in this thesis. The new transonic aeroelastic rig consists of a linear cascade wind tunnel with a vibrating blade driven by piezoelectric actuators. The primary layout was determined by a comparative discussion based on an overview of several aeroelastic rigs and transonic cascade wind tunnels. The blade profile was obtained from the GKN Virtual Integrated Compressor (VINK). The vital part was the design of the test section, which was optimized with the numerical simulations to obtain an optimal flow in the test rig. The transonic nozzle design was developed with the Foelsch method.
Numerical simulations were performed to evaluate the expected performance of the chosen test rig design. The veracity of the numerical model was checked by validation with experimental data obtained from the constructed test rig. Three different mode shapes and five cases with variable tip gaps were analyzed. The unsteady results provide a benchmark for the test rig. The unsteady distribution on the blade due to the vibration of each mode predicts the unsteady performance which will occur in the unsteady testing. The comparison with different tip gaps shows that these are significant for both periodicity and unsteady performance. Moreover, the study highlights the discrepancies in the unsteady perturbation behavior between the test rig flow and an ideal turbomachinery flow. This is due to system discrepancies is evaluated, and several are mostly unavoidable for future testing.