The inuence of steady loading parameters on low-pressure turbine flutter
Aeroelastic utter is a major concern of turbomachinery engineers. As such, this poten- tially catastrophic self-excitation mechanism has been the focus of many research endeavors. While most investigations have concentrated on identifying key correlations between flut- ter and unsteady parameters (e.g. reduced frequency or mode shape), little consideration has been given to inuence of steady blade loading. This paper examines the inuence of steady loading parameters on the aerodynamic damping of low-pressure turbine (LPT) blades commonly seen in aircraft gas turbine engines and power turbines. Frequency do- main RANS CFD is used as a computational wind tunnel to investigate two different LPT geometries: 1) a quasi-2D slice of EPFL's non-rotating Standard Configuration 4 and 2) a full 3D LPT blade from a new test rig at the Institute of Turbomachinery and Fluid Dynamics in Hannover, Germany. To vary the loading, the back pressure is incrementally varied consequently shifting acoustic resonance conditions and altering the passage shock structure. Results are then tabulated for all nodal diameters for various mode shapes and reduced frequency. Ultimately, it is concluded that steady blade loading carries a signif- icant impact on the aeroelastic stability of LPT blades and is a quite sensitive to mode shape in a similar fashion as the well-known critical reduced frequency parameter.
