Flow-induced vibration of elastically supported rectangular cylinders

Abstract

<p>Eight rectangular cylinders with aspect ratios that varied from 2 to 7 tested in the wind tunnel at zero degree incidence in a nearly turbulence-free flow field. The models were elastically suspended in the wind tunnel and constrained to a single degree of freedom, vertical motion transverse to the wind flow direction.;Five tests were conducted for every aspect ratio, each with a different system mass. Side plates were utilized to minimize three-dimensional flow effects at the ends of the models and to maximum the two-dimensional flow field.;Prior to testing each model, the following dynamic parameters were determined: natural frequency, mass, stiffness, damping, and Scruton number. Each test began with the model motionless. The wind speed was incrementally increased until vortex-induced transverse vibrations were observed. At each increment of wind speed where transverse vibrations were observed, the maximum amplitude of vibration and the wind speed were recorded.;All models exhibited vortex-induced vibration lock-in during at least one wind regime. Five models exhibited vortex-induced vibration lock-in during two wind regimes. All models exhibited vortex-induced vibration lock-in at the critical reduced velocity predicted by the modified Strouhal number.;Experimental results for each of the forty test cases include the reduced amplitudes and reduced velocities during lock-in, confirmation that lock-in can occur during more than one wind regime, and confirmation that the modified Strouhal number accurately predicts the reduced velocity when lock-in commences.;The relation between the reduced amplitude and the mass/damping parameter was studied. As a result, a parameter for rectangular cylinders was derived as a function of the mass, damping, and geometry of the system. This parameter is analogous to the mass/damping parameter for circular cylinders, the Scruton number. Finally, a single response equation was developed that predicts the amplitude of vortex-induced vibration for a rectangular cylinders with aspect ratios from 2 to 7 utilizing the mass/damping/geometry parameter derived as part of this study.</p>