Experimental Investigation of Unsteady Flowfield in a Supersonic Cascade Oscillating in Bending Mode

Abstract Experimental investigation of unsteady flowfield in a supersonic cascade oscillating in bending mode was conducted in both low supersonic inlet flow and low back pressure cascade conditions, using a controlled-oscillating annular cascade test facility. A newly developed high speed mechanical drive system in the facility imparted the controlled oscillation in bending mode to all the 16 blades composing the annular fan blade row. The system can oscillate the blades at a constant oscillatory amplitude and at constant interblade phase angles, in both aerodynamic stable and unstable domains of the blade row. Chordwise distributions of unsteady aerodynamic pressures acting on oscillating blades were measured in both aerodynamic unstable and stable domains by an indirect unsteady pressure measuring method, In addition, unsteady aerodynamic forces produced by shock wave movement due to the blades oscillation were precisely examined. Those data were jointed to evaluate the nature of cascade flutter. The experimental results showed that unstalled supersonic bending mode fan blade flutter could occur with the strong effect of unsteady aerodynamic force produced by shock wave movement. This paper also touches on the comparison between nature of low back-pressure fan blade flutter in bending mode and that in torsional mode.