Design and Experimental Verification of Mistuning of a Supersonic Turbine Blisk

A rotor blisk of a supersonic space turbine has previously been designed to allow for free flutter to occur in an air test rig (Groth Mårtensson, and Edin, 2010, “Experimental and Computational Fluid Dynamics Based Determination of Flutter Limits in Supersonic Space Turbines,” 132(1), p. 011010). Flutter occurred at several operating conditions, and the flutter boundary for the test turbine was established. In this paper the rotor blisk is redesigned in order to inhibit flutter. The design strategy chosen is to introduce a mistuning concept. Based on aeroelastic analyses using a reduced order model a criterion for the required level of mistuning is established in order to stabilize the lower system modes. Proposals in literature suggest and analyze mistuning by varying blade mode frequencies in random patterns or by modifying blades in an odd-even pattern. Here a modification of sectors of the blisk is introduced in order to bring a sufficient split of the system mode frequencies. To verify that the redesigned blisk efficiently could inhibit flutter, an experiment similar to that in the work of Groth et al. is performed with the mistuned rotor blisk. By running the redesigned blisk at operating conditions deep into the unstable region of the tuned blisk, it is demonstrated that a relative low level of mistuning is sufficient to eliminate rotor flutter.