Acoustic flutter control of three-dimensional transonic rotor flow

The fundamentals associated with the three-dimensional effects of acoustic excitation and flutter suppression in a transonic turbomachinery flow are studied. A high-resolution aeroacoustic Euler flow solver that can capture shock waves and resolve acoustic waves was developed and validated. This numerical procedure employs the modified Osher-Chakravarthy upwind total variation diminishing scheme for acoustic and discontinuity capturing. Time accuracy is accomplished by using implicit approximate lower-upper factorization together with Newton subiterations. Sound source modeling and characteristic far-field treatment are carefully implemented to result in an accurate aeroacoustic solver. Numerical simulation of a three-dimensional transonic rotor blade row (NASA rotor 67) is performed. Both internal and external acoustic excitations have been studied to investigate these acoustically excited flowfields. It is found in the present simulation that internal trailing-edge forcing is 3-5 times more effective than that excited by means of external methods, although the internal hardware implementation is much more difficult. External casing forcing of rotor 67 operated at peak-efficiency condition was also simulated. The physical mechanism of how a ducted transonic rotor flow that can be externally excited is explained. It is concluded that blade flutter in a three-dimensional turbomachine can be acoustically suppressed, either internally or externally, provided a proper control logic and sensor device is selected.