Aeroelastic properties of closely spaced modes for a highly loaded transonic fan
2008 (English)Conference paper (Refereed)
In the design of modem compressor blades of wide chord (low aspect ratio) type it is often hard to avoid having modes that are close to each other in frequency. Modes which are closely spaced can interact dynamically. Mistuning and localization of stresses are known problems with this. A potential problem with this is also the possibility of coalescence flutter of the modes. Even if the modes are frequency separated at zero rotational speed, the centrifugal stiffening may cause the modes to attract and even cross (or veer) at some rotational speed. In design, mode separation criteria are sometimes applied in order to minimize the risk of encountering unknown dynamic phenomena. This study is performed to better understand the dynamics of closely spaced modes with respect to risk for coalescence flutter. A reduced order aeroelastic system is then constructed that describes the interaction between the different modes. The aeroelastic couplings are then calculated for the 2 mode system. The method is general in terms of mode shapes and number of interacting modes. A parametrical study is performed in order to study how strongly the modes interact when the frequency separation is decreased and if there is a risk of destructive coalescence flutter. The investigation is performed on a high pressure ratio front stage fan blade. The tendency of the modes to interact depends on the strength of the coupling compared to the strength of the pure structural modes. The tendency towards instability was increased in cases where the stability margin was smaller of the single modes. The results can be considered to support a separation criterion of 2% for the lower. A re-evaluation should be considered if lighter blade material and increased loads are to be used.
Place, publisher, year, edition, pages
2008. no PART A, 509-518 p.
, Proceedings of the ASME Turbo Expo, 5
Aeroelastic coupling, Aeroelastic properties, Aeroelastic system, Centrifugal stiffening, Compressor blades, Different modes, Dynamic phenomena, Fan blades, Frequency separation, High pressure ratio, Low aspect ratio, Mistuning, Mode separation, Mode shapes, Potential problems, Re-evaluation, Reduced order, Rotational speed, Separation criterion, Single mode, Stability margins, Structural modes, Aspect ratio, Centrifugation, Flutter (aerodynamics), Coalescence
IdentifiersURN: urn:nbn:se:kth:diva-154115DOI: 10.1115/GT2008-51046ScopusID: 2-s2.0-69949187258ISBN: 9780791843154OAI: oai:DiVA.org:kth-154115DiVA: diva2:758117
2008 ASME Turbo Expo; Berlin; Germany; 9 June 2008 through 13 June 2008
QC 201410242014-10-242014-10-142014-10-24Bibliographically approved