Effect of Adjacent Blade Motion on the Aerodynamics of a Linear Cascade Blade

Due to the trend of increasing power and reducing weight, the fan and compressor blades of turbo machinery might be more sensitive to flutter, which must strictly be avoided in the design process. In order to increase our understanding of the flutter phenomena for fan and compressor cascades, aero-elastic investigations are essential. In the present work experiments were performed in the specifically designed Oscillating Cascade Facility to investigate and quantify the unsteady aerodynamics forces and moments acting on a blade in a linear cascade of blades when the instrumented blade is stationary and the two adjacent blades on both sides of the instrumented blade are executing torsion-mode oscillations about their mid-chord. A 5-component strain gage balance was used to measure the unsteady aerodynamic forces on the model blade. The forces were measured for six inter-blade phase angles (i.e., the phase angle between the moving blade motions at a given frequency where the central blade is stationary) at low subsonic conditions, different reduced frequencies and different stagger. The time-variant forces were analyzed and variation of lift and drag coefficients for different inter-blade phase angles and reduced frequencies were plotted. The experimental results indicate that the inter-blade phase angle had a major effect on the variation of the unsteady forces and that reduced frequency had a somewhat less significant effect. Also in order to investigate the influence of the reduced frequency and inter-blade phase angles on the global stability of the cascade and its local contributions, experiments were performed for different reduced frequencies and phase angles. At the higher inter-blade phase angles (180°) the blade remains aerodynamically stable at 0° stagger, but the stability reduces at higher stagger angles. The blade is usually unstable when the interblade phase angle is 0°. At different flow conditions, some of the inter-blade phase angles appear to be aerodynamically unstable.