Forced Response Experiments in a High Pressure Turbine Stage

Abstract

An experimental investigation was conducted on a single stage high pressure turbine in order to gain a deeper understanding of turbine blade forced response. In particular the main objective of this experiment was to obtain good quality validation data for the prediction methods used by major engine manufactures. The stage investigated consists of an uncooled nozzle guide vane (NGV) and a rotor with 64 blades. To study the complete forced response problem a so called Flexible Rotor was designed and manufactured. This rotor has three modes of interest in the operating range of the stage: first torion, second flap and third edge. The design of experiment was supported by detailed CFD and structural analysis. The mechanical behavior of the Flexible Rotor is well known. In order to identify all interesting modes, all blades are equipped with strain gauges, individually calibrated. To check the unsteady pressures, 18 unsteady pressure transducers were mounted at midspan. This paper deals with experiments only with the Flexible Rotor. Forced response results are presented for the first torsion mode at different pressure ratios. The result obtained, show a large scatter for the maximum response amplitudes at each pressure ratio. This distribution of the amplitudes around the disk is controlled by the mechanical properties of the rotor.