Influence of various design parameters and unsteady flow on the fluid-structure interaction of a lightly cambered blade in a cascade

The aim of this paper is to report the results of the fluid-structure interaction study of a lightly cambered blade in a cascade under the influence of various inflow conditions and structural parameters, in a cost-effective manner. This work could be viewed as a preliminary design tool that provides the behavioral trend of the blade motion which will be useful when a detailed analysis has to be performed. The methodology employed to formulate the aerodynamic model for lightly cambered airfoils follows the Whitehead's aerodynamic theory for a cascade of flat plates. The aerodynamic loads acting on a blade in a cascade of airfoils are computed to provide the required conditions for the structural model. The aeroelastic model thus formulated is employed to predict the structural response of a blade in a cascade subjected to both steady and unsteady flows. The possibilities of a blade undergoing pure bending or torsion, or coupled bending-torsion flutter are investigated in the present study. The utility of the already developed aerodynamic model is demonstrated by investigating the structural behavior of three different blade curvature profiles - Double Circular Arc (DCA), NACA 65, and NACA a=1.0 mean lines. The effects of various blade structural parameters such as mechanical damping, center of gravity and elastic axis offset, and cascade geometric parameters such as stagger angle and blade spacing on the blade aeroelastic response are analyzed. The flutter boundary for a range of frequency ratios is then examined. It has been found that compressor blades with frequency ratios close to unity are vulnerable to coupled bending-torsion flutter under the influence of an incoming steady flow. The growing torsional vibrations are in general registered for higher values of air velocity compared to the range of velocities favoring bending flutter. The influence of different compressor unsteady flows - rotating stall and surge, on the aeroelastic behavior of a lightly cambered blade is also examined in the present study.