Aerodynamically excited vibrations of a 3-inch x 3-inch aluminium angle in steady flow

Abstract

A 3-in. x 3-in. x 3/IG-in. aluminum angte was mounted across the working section of the National Aeronautical Establishment's I5-ft. wind tunnel, and the beam vibrations excited by steady flow were studied. The beam was instrumented ta provide indications of amplitude, mode, and frequency. Beam vibrations are correlated with measurements of rigid body eddy shedding frequencies and beam natural frequencies. A controlling effect on vibration amplitude appears in several instances to arise from the eddy shedding being contrained to occur at tbc beam natural frequencies . Quasi-steady expressions for aerodynamic damping have been developed for pure flexural vibrations in the plane of symmetry as well as for coupled torsional-flexural vibrations. The damping has been evaluated using measured values of steady sectional lift, drag, and pitching moment, and negative damping is predicted for a narrow range of angle of attack.