Numerical models for the vibration response of high pressure compressor rotors with validation for forced response and surge

The following dissertation contributes to the numerical modelling of the vibration response of integral real high pressure compressor rotor blades. It aims to validate the chosen modelling techniques with available measurement data and to demonstrate its capability for industrial applications. In detail the present dissertation investigates two different scenarios of blade excitation. Within the first scenario the predicted blade response of an integral bladed rotor is compared to measurements with focus on the blade mistuning problem. The second scenario deals with vibration response of compressor rotor blades due to surge of a transonic high pressure compressor. For the modelling purpose of the aeroelastic interaction a loose coupling technique is selected with a separate structural and flow model. The chosen structural model is based on the modal reduction technique published by Yang and Griffin, called subset of nominal system modes. The high accuracy of the model when reducing finite element models is discussed. It is shown, that the reduction algorithm is limited to mistuned modeshapes that can be expressed by a superposition of the tuned modeshapes of the rotor. The 3D Finite Volume Code AU3D, developed at Imperial College London, is used to model the steady and unsteady flow field. The flow solver is utilised to derive the external and motion induced aerodynamic forces for both investigated scenarios. To reduce the numerical effort an additional 1D flow solver is developed that allows the surge frequency and impulse loads for the compressor to be computed. The presented comparisons between measured and predicted vibration responses for the integral resonance passing are in a high agreement. The remaining deviations are within the measurement accuracy. In addition, it is demonstrated that the applied model can also be used for model identification purposes from measurement data. It is found that the investigated surge can qualitatively be well explained by the impulse loads that are generated due to the fast change of the aerodynamic loads. The predicted vibration levels are quantitatively and qualitatively in good agreement to the measured data. It is shown that further analysis is required to understand the considerable scatter in vibration response of successive surge cycles.