Development of a benchtop testing methodology for determining turbine blade vibration amplitude relative to input energy

Turbocharger blade vibration experiments are important tasks and assist in identifying vibration parameters. Blade vibration amplitudes vary from blade to blade due to the casting process causing different blade geometry. Blade tuning can increase the risk of failure due to the frequency linkage between the blades. Most commonly the blades on the turbine side are designed identical but during casting, blades are developed non identical, and the system is called mistuned. 

This study describes the procedure and the methodology developed to form a turbine wheel model and fit it with experimental data with the aim to rank the blades in terms of how responsive they are.  The methodology suggests that the process is done for each desired wheel in a population and once the parameters are identified, some of the parameters can be used for other wheels of the same type. 

To achieve the objective, this study analyses multiple vibration excitation and measurement methods in order to determine which method is the best to be used. As the turbine wheel is a very complex system, the turbine blade was modelled as a cantilever beam and an optimisation method was developed to fit the experimental data with the model data. From the optimised parameters found based on the cantilever beam section; a paddle wheel rotor was formed with the known beam parameters and a core with unknown parameters. The model’s core (hub) parameters were identified using the optimisation process developed by using a rotor system with 4 beams. Finally, the model was expanded to match the turbine wheel blade number. On a parallel workstream, multiple excitation and measurement methods were investigated, and the best methods were chosen to develop a final rig (best method in terms of repeatability, reproducibility, continuous excitation, and dwell excitation). This thesis developed a new process (method) for frequency and peak response identification of damped and undamped turbine blades. The main contribution involves cantilever beam-core model structures and experimental processes for identification of the model parameters and a final test rig is proposed as a recommendation.