Aeroelastic investigation of an open 3D steam turbine test case and blade shape optimization with improved flutter behavior

Abstract

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 blade geometry with higher efficiency and an improved flutter stability. 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 on the original geometry, obtained by a non-linear method, are compared with those already published by other researches with different flutter approaches. The present results are in complete agreement with numerical investigations already present in the literature and show a high blade instability for the first bending mode. Starting from this unstable geometry, a shape optimization procedure with aeromechanical constraints has been applied in order to obtain a blade with improved performances from both the aerodynamic and the flutter point of view. The optimum profile shows a higher efficiency and a flutter instability reduction. Those aspects are exhaustively discussed and comparisons with the baseline geometry are reported. KEYWORDSCFD, FLUTTER, OPTIMIZATION, STEAM TURBINE NOMENCLATURE ṁ mass flow p pressure Greek: η T T total-to-total stage efficiency ω * reduced frequency, = ω * c/v out σ static stress ξ logarithmic decrement (log.dec.

Aerodynamic and aeroelastic computations of a last stage steam turbine using harmonic balance methods

“…The overall results were deemed to be in good agreement with (Qi et al, 2017) using the flow solver LUFT. (Pinelli et al, 2021) used non-linear method to obtain the aerodynamic damping and found good agreement with previous studies. An aeromechanical optimization workflow is established, and aerodynamic/aeromechanical performance of the optimum blade profile is compared to the baseline geometry.…”