Torsional flutter of unstalled cascade blades at zero deflection

Abstract

The report presents the results of theoretical calculations of torsional flutter of unstalled cascade blades. It is shown that the position of the torsional axis is of great importance, the best position being near the quarter-chord point, and the worst position near the threequarter-chord point. An unfavourable axis position gives flutter speeds which are exceeded in normal machines. An experimental investigation in an annular cascade with twelve blades confirms the existence of this type of flutter. Good agreement with the theory is found in some cases, but in others it is thought that three-dimensional effects are having a substantial influence. The effects of small differences between blades are examined theoretically in an Appendix, and it is concluded that the effects of mistuning and mechanical damping are always favourable.