Aeroelastic Investigation of an Open 3D Steam Turbine Test Case and Blade Shape Optimization with Improved Flutter Behavior

The paper describes the flutter stability assessment of a steam turbine rotor and the application of a multi-disciplinary shape optimization procedure to obtain a new flutter-free profile. The investigated test case consists of a steam turbine last stage representative of modern industrial steam turbine blading, firstly presented by Durham University and intensively investigated during last years. The aerodamping results of the original geometry, obtained by a non-linear method, are compared with those already published by other researches with different flutter approaches (linearized, harmonic balance, non-linear). The present results are in complete agreement with numerical investigations already present in the literature and show a high instability for the first bending mode. Starting from this unstable geometry, an aeromechanical shape optimization procedure has been applied in order to stabilize the rotor row while maintaining similar aerodynamic performances and constraints. The optimum profile shows relevant improvements in terms of flutter stability, which are exhaustively discussed and compared with the original geometry.