Interference galloping-investigations concerning the phase lag of the flow switching

Abstract Slender cylinders close together may be exited to self-sustained oscillations which are associated with a hysteretic flow switching in the gap between the two cylinders. Measurements have shown that this flow switching appears with a time resp. phase lag, so that energy can transfer from the flow to the structure. In this study new model tests have been done to determine the flow direction β k where the flow switching occurs. This has been done by flow visualisation technique with a milk probe in a water channel. It was found that for a forced oscillation β k is a function of the reduced velocity U R . Comparisons with the quasi-static values β kst lead to the phase lag Δϕ of the flow switching. Together with quasi-static force coefficients c L measured in former investigations these data have been used as a basis for calculations of force-displacement diagrams which describe the energy input into the oscillating cylinder.