Nonlinear aeromechanics and fatigue life prediction of compressor blades

Xiaoguang Li, Purdue University

Abstract

A mathematic model is first developed and utilized to study the effects of separated flow, including dynamic stall, on stall flutter. Nonlinear flow induced airfoil response, including periodic and chaotic motions, is investigated using a typical section airfoil and a semi-empirical dynamic stall model. It is shown that the developed nonlinear aeroelastic models can capture the essential dynamics of the airfoil system, and provide fundamental understanding about the underlying mechanism which can not be predicted from linear analyses. In particular, bifurcations and routes to chaos are identified. These nonlinear aeroelastic analyses explain why and when complicated oscillations can happen in a nonlinear aeroelastic system. The feasibility of active suppression of the nonlinear stall flutter using piezoelectric actuators, including the control of the chaotic behavior, is then examined. Linear quadratic regulator method is used to design a controller based on linearized, approximate equations of motion. Next, the feasibility of the nonlinear blade flutter suppression using piezoelectric actuators is explored using a different model, with a cantilevered flat plate being the structural model. This study is also concerned with high-cycle fatigue (HCF) life prediction. Probabilistic dynamic stall and unstalled flutter generated HCF analyses for turbomachinery blading were developed. The models consider the stall and unstalled flutter of a cantilevered flat plate, with the unsteady aerodynamics determined from a semi-empirical nonlinear dynamic stall model and a linearized incompressible unsteady aerodynamic model for airfoil cascades. The resulting probabilistic HCF model utilizes both a fracture mechanics approach and a cumulative linear fatigue damage model, with the crack size and cumulative fatigue damage index considered as random variables.

Degree

Ph.D.

Advisors

Fleeter, Purdue University.

Subject Area

Mechanical engineering|Aerospace materials

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