PREDICTION OF TURBINE ROTOR BLADE FORCING DUE TO IN-SERVICE STATOR VANE TRAILING EDGE DAMAGE

In the following paper we will present an overview on the results of a research project whose objective is the assessment of the influence of trailing edge material loss of high pressure turbine nozzle guide vanes onto the low engine order excitation of the downstream rotor blade. To quantify the forcing, the modal forces for the rotor eigenmodes of interest are obtained by solving the unsteady Navier-Stokes equations for a full assembly of stator and rotor ring. Since the computing resources for such a calculation are too high to be routinely employed for the assessment of in-service damage patterns, an important task of the project was to investigate quick alternatives to the costly CFD simulations. The approach chosen is to perform a sufficient number of forced response calculations with different damage patterns in advance and use the results to build a surrogate model that can be used to assess the severity of damage patterns by simple interpolation. We will first present the analysis chain employed to quantify the forcing, next describe the approach to build a surrogate model with special focus on the generation of an optimal DoE matrix, and finally discuss the prediction accuracy of the surrogate model. It is shown that an interpolating surrogate model, based on radial basis functions, can successfully be used to predict the rotor forcing for damage patterns that were not analyzed using the costly CFD calculations beforehand.