Preliminary flutter design method for supersonic low pressure turbines
The "Tie-Dye" (TD) method is a well-known preliminary flutter design method for subsonic low pressure turbine (LPT) blades. In this paper, a study of 2D mode shape sensitivity using the TD-method for supersonic exit Mach numbers is presented. Using a harmonic balance CFD method, TD maps displaying the critical reduced frequency for a range of pitching axis locations were created. The TD method was run on two geometrically different blades. Subsonically, the characteristic appearance does not change much over airfoil types. An even lesser amount of morphing can be observed between the different profiles in the supersonic range, than for the subsonic cases. Pure bending modes show a high sensitiviy to the actual bending direction. Therefore the single critical reduced frequency value criteria does not hold up for all cases. The method is applicable for supersonic exit flows, and is even more predictable and universal than for the subsonic cases. Copyright © 2009 by ASME.
