INFLUENCE OF DETAILING ON AERODYNAMIC FORCING OF A TRANSONIC AXIAL TURBINE STAGE AND FORCED-RESPONSE PREDICTION FOR LOW-ENGINE-ORDER (LEO) EXCITATION

The effects of detailing on the prediction of forced-response in a transonic axial turbine stage, featuring a parted stator design, asymmetric inlet and outlet casings as well as rotor cavities, is investigated. Ensuring the mechanical integrity of components is of paramount importance for the safe and reliable operation of turbomachines. Among others, flow induced resonance excitation can lead to high-cycle fatigue (HCF) and potentially to damage of components unless properly damped. This numerical study is assessing the necessary degree of detailing in terms of spatial and temporal discretization, boundary conditions of the pre-stressed rotor geometry as well as geometrical detailing for the reliable prediction of the aerodynamic excitation of the structure. In this context, the sensitivity of the aerodynamic forcing is analyzed by means of the generalized force criterion, showing a significant influence for some of the investigated variations of the numerical model. Moreover, the origin and further progression of several low-engine-orders (LEO) within the flow field, as well as their interaction with different geometric details has been analyzed based on the numerical results obtained from a full 360 degrees CFD-calculation of the investigated turbine stage. The predicted flow induced vibration of the structure has been validated by means of a full forced-response analysis, where a good agreement with tip-timing data has been found.