Experimental Investigations of Stall Flutter in a Transonic Cascade Free

The design of modern gas turbines is more and more based on flow simulations by numerical calculation models. Due to the different influence parameters the development and verification of these codes requires detailed data bases, which can only be provided by experimental investigations. The demand of increasing power density leads to higher Mach Numbers up to transonic ranges. Due to the thin blade profiles the risk of stall flutter becomes an extraordinary point of interest. Therefore, in a transonic wind tunnel a cascade of nine compressor blades designed by MTU Munich were investigated at different inlet Mach numbers and incidence angles. To get information about flow behavior at steady state, profile pressure distribution was measured at midspan with pressure taps on profile surface. In order to provide information about the overall flow field oil flow visualization and Schlieren technique were applied for the investigation at steady state. For flutter simulation the blade in the middle position of the cascade was forced to torsional oscillating movement by an electromagnetic shaker system with a frequency of f = 310.0 Hz. The flow behavior with oscillating and fixed center blade was investigated at midspan by means of dynamic pressure transducers and hot films glued on profile probes. The results of these investigations are presented in this paper especially up to the appearance of stall flutter.