The validity of quasi-steady theory, using experimental aerodynamic coefficients, to explain the observed aeroelastic instability of bluff cylinders in a uniform stream is examined for several cylinder sections. Only plunging oscillation is considered, and the analytical model is an oscillator with nonlinear damping dependent on the aerodynamic coefficients. Static and dynamic wind-tunnel tests were made of cylinder models of square, rectangular, and D-section. The D-section and the short rectangular sections behaved dynamically like the circular cylinder, showing plunge instability only near resonance with the von Karman vortex street. In complete contrast, the square and long rectangular sections showed plunge instability with amplitude increasing with wind speed for all speeds above a critical value. These dynamic results were in quite good agreement with the theoretical predictions, using the static test data.

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