Investigation of Mistuning Effects on Cascade Flutter Using a Coupled Method

Effects of frequency mistuning on cascade flutter are studied using a computational method with coupled structural dynamics and aerodynamics. An implicit finite-volume scheme of second-order accuracy is used to solve the unsteady Euler equations. The structural equations with bending and torsional degrees of freedom for a rigid blade profile are integrated in time simultaneously with the flow equations. Investigations are performed on flutter of a turbine cascade in bendingmotion andwith alternatemistuning of the structural eigenfrequency. Previousworkby an uncoupled method shows a beneficial effect of alternating frequency mistuning on flutter stability. This paper shows that fluid–structure interaction tends to decrease the effective amount of mistuning. There exists a minimum amount of mistuning required to stabilize the cascade. The same qualitative behavior is shown to exist with a compressor cascade. Nomenclature b = half-chord of blade Cl = lift coefficient Cm = moment coefficient about the elastic axis h = translational displacement of the blade Kh = bending stiffness of the blade K = torsional stiffness kc = reduced frequency,!c=2U1 m = mass per unit span of blade rb = radius of moment of inertia about elastic axis xb = distance between center of gravity and elastic axis = rotational displacement of the blade = mass ratio, m=1b2!h = natural angular frequency for translation! = natural angular frequency for rotatio