A nonlinear integrated aeroplasticity method for the prediction of turbine forced response with friction dampers (Q1348427)

The authors present an integrated aeroelasticity model for turbine blade forced response predictions. This approach requires an integration of unsteady aerodynamics with nonlinear structural dynamics, the letter arising from the use of root friction dampers to dissipate the energy, so that the response levels can be kept as low as possible. The inclusion of friction dampers is known to raise the resonant frequencies from the standard assembly frequencies, a shift that has not been known prior to the aeroelasticity calculations. An iterative procedure is therefore developed in order to determine the resonance shift under the effects of both unsteady dynamic loading and nonlinear friction dampers. The iterative procedure uses a viscous nonlinear flow model for evaluating the aerodynamic forcing. The methodology is applied to a high-pressure turbine rotor where the resonances of interest are due to the first torsion and second flap blade modes under 40 engine-order excitation. The forced response computations are conducted making use of a multi-blade row approach in order to avoid errors associated with ``linking'' single blade row computations. The predicted frequency shifts and the dynamic behaviour of the friction dampers are found to be within the measured range. Furthermore, the measured and predicted blade vibration amplitudes show a good agreement with available experimental data.