Influence of Intrarow Interaction on the Aerodynamic Damping of an Axial Turbine Stage

The present numerical study aims at examining the influence of intrarow interaction effects in aerodynamic damping predictions of an axial turbine rotor. The investigated operating point corresponds to a resonance crossing associated with the fundamental engine order of the stator blade row. Accordingly, the pressure perturbations induced by the vibration of the rotor at its modal frequency are found to be coincident in frequency and thus superimpose with the pressure perturbations resulting from intrarow interaction phenomena. A methodology for extracting vibration induced pressure perturbations for the subsequent calculation of the vibration induced modal aerodynamic damping is established and applied within the scope of the present study. Applying this methodology, both the influence of the underlying mean and transient flow field as well as the influence of acoustic wave reflections at the adjacent stator blade row is investigated on the predicted aerodynamic damping. In this context, the underlying mean flow field, which is found to be slightly altered in the presence of intrarow interaction phenomena, was proven to have a significant influence on vibration induced pressure perturbations. Moreover, acoustic wave reflections at the adjacent stator blade row are found to have the capability of influencing the aerodynamic damping depending on their actual phasing when impinging onto the turbine rotor.