A quasi-steady 3 degree-of-freedom model for the determination of the onset of bluff body galloping instability

Abstract

In this paper, a quasi-steady three degree-of-freedom (3-dof) flow-induced galloping instability model for bluff-bodies is proposed. The proposed model can be applied generally for the prediction of onset of galloping instability due to negative aerodynamic damping of any prismatic compact bluff body in a fluidic medium. The three degrees of freedom refer to the bluff body's two orthogonal displacements perpendicular to its length axis and the rotation about its length axis. The model incorporates inertial coupling between the three degrees of freedom and is capable of estimating the onset of galloping instability due changes in drag, lift and moment, assuming that the bluff body is subject to uniform flow and motion. The changes may be a function of wind angle of attack ( α) perpendicular to bluff body's length axis, Reynolds number and a skew wind angle ( ϕ) in relation to the length axis of the bluff body. An analytical solution of the instability criterion is obtained by applying the Routh–Hurwitz criterion.