Nonlinear flow-induced resonances of an H-shaped section

Abstract

The flow-induced vibrations of an H-shaped model (simplified Tacoma profile) in incompressible flow were investigated in a high-pressure wind tunnel. Unlike the most commonly applied method which calls for an elastically mounted rigid section, a slender and thus elastic beamlike model was used, the ends of which were fixed to a stiff and sensitive piezo-balance. Hence, in the case of vortex resonance, the section vibrates near its fundamental bending or torsional eigenfrequency. The corresponding response characteristics—obtained by measuring the rms values of lift and moment depending on the flow speed—show the typical features of nonlinear vibration behaviour: resonance peaks bent to the left or right, secondary resonances up to the sixth order, subharmonic resonance, hysteresis jumps and frequency shifts of the resonance peaks. In addition, the steady and unsteady aerodynamic forces on the section at rest were measured at Reynolds numbers up to 1.25 × 106, supplying information on the Strouhal number and the power spectrum. Concerning the galloping behaviour, the measured lift and moment characteristics show that the H-section is aeroelastically stable in bending and unstable in torsion even at high Reynolds numbers.