Keynote: Paradigmatic experiments for flow-induced vibrations

Abstract

The initial, or general transient temporal behaviour of flow induced vibrations was studied particularly with regard to the question, up to which extend self-excited, flow-induced vibrations can be described by the Landau Equation. Three different cases were studied experimentally, using bodies with generic shape. The first case represents bluff bodies, a simplified section of the Tacoma bridge, which has a torsional degree of freedom. The second case is an two-dimensional airfoil in transonic flow having an heave and torsional degree of freedom. The third case is an elastic half-wing model, also investigated in transonic flow. It is shown that in all three cases, beyond the critical point and at small initial amplitude the temporal development of the oscillations up to the limit cycle i.e. the envelope of the measured time functions, agrees with the corresponding curve, given by the solution of the Landau equation. For the Tacoma section and the airfoil the same agreement was demonstrated for initial amplitudes much larger than the limit cycle one. In addition for both last cases the bifurcation behaviour was investigated and as outcome the Landau constants were determined. Finally it is tried to give an elementary physical explanation for the instability phenomenon.