Final work : Flutter wizard: development of an automatic tool for safety prediction in compressors and turbines

Abstract

One aeroelastic phenomenon that has to be avoided at all costs in turbomachinery is flutter. Flutter is a self-sustained and self-excited excitation that jeopardizes the structural life in a matter of seconds. This phenomenon is highly dependent on multiple parameters that makes it unable to be predicted a priori. A key factor is the variation of the inter blade phase angle that must be assessed at each operational condition to guarantee the machine integrity. This process generates an enormous amount of computational flutter analysis that is performed manually increasing the engineering time, and it is dependent on the user's expertise. Producing a need for reproducing reliable results without any user interaction resulting in an engineering time reduction. This need was satisfied by the development of a flutter wizard tool, which works within FINE\texttrademark/Turbo. The tool is able to set up and analyze a single or multiple rows for one vibrating blade, at one or multiple operational conditions with or without custom user inputs. By making use of the developed flutter wizard tool the engineering time required was strongly reduced, it only took approximately 1.5\% of the time when compared to a manual set up and analysis. The wizard also provides a flexible and user-friendly set up so the client can reproduce complex or particular cases if desired. Seven cases were analyzed with a variety of geometry, operational conditions imposed motion and imposed. Six cases were contrasted against experimental and numerical data, while the seventh just against numerical data from two software. A close match between steady-state experimental and current results was found in all cases, except where non-linear effects were encountered. A total of 153 non-linear harmonic cases were run with the wizard, in which for an operational condition it provided a direct output of the aeroelastic stability of the system by means of the aerodynamic damping coefficient. A proportional aerodynamic damping coefficient curve per reference was used, as it proved to remove the scaling factor and retrieve the proportional aerodynamic work for each case with a better agreement among results. A manual detailed analysis of the harmonic content at specific blade height locations were performed to validate results. Thus, a collection of results is gathered and analyzed in detailed, providing a description and correlation of the steady and unsteady results. Finally, future work is proposed as a benchmark on a last stage steam turbine, as the actual machine and stator/rotor interaction is taken into account.